Exposure Controlling System and Interchangeable Lens Therefor

1. Field of the Invention

This invention relates to an exposure controlling system for an interchangeable lens and an interchangeable lens which are particularly suitable for exposure control of a single lens reflex camera for which a cata-dioptric lens is provided as one of interchangeable lenses.

2. Description of the Prior Art

Conventionally, single lens reflex cameras having AE (automatic exposure) and AF (automatic focusing) functions of the TTL (through the lens) type have been put to practical use. As interchangeable lenses for such single lens reflex cameras, various lenses have been developed wherein information regarding AE and AF functions is fixedly stored such that it may be read from a body of a camera on which the lens is mounted.

It has been proposed for such a single lens reflex camera to make exposure control of the stopping down light measuring method when mounting of an interchangeable lens is not confirmed. However, such exposure control is not prepared for mounting of a catadioptric lens.

Such a single lens reflex camera having AE and AF functions of the TTL type as described above is not prepared for use of a cata-dioptric lens as an interchangeable lens principally from a restriction in detection of a focus condition. Accordingly, no consideration is given either to exposure control for coping with a cata-dioptric lens. While cata-dioptric lenses which can be mounted on such a single lens reflex camera are on the market, if a cata-dioptric lens is mounted on such a single lens reflex camera as described above, the body of the camera cannot read necessary information from the interchangeable lens. Consequently, the camera body will not conduct detection of a focus condition and will make the same exposure controlling operation as that when no interchangeable lens is mounted. Accordingly, there is a problem that functions of the camera body are restricted significantly when a cata-dipotric lens is used.

It is an object of the present invention to provide an exposure controlling system wherein functional restrictions are little even when a cata-dioptric lens is mounted as an interchangeable lens and also provide an interchangeable lens for such an exposure controlling system.

In order to attain the object, according to one aspect of the present invention, there is provided an exposure controlling system for an interchangeable lens, comprising a reading means for reading data regarding aperture values of the interchangeable lens from the interchangeable lens, a light measuring means, and means responsive to outputs of the reading means and the light measuring means for finding, when the interchangeable lens is an ordinary lens, a combination of an aperture value and an exposure time to which the ordinary lens can be controlled to provide an appropriate exposure and indicating the aperature value and the exposure time thereon and for finding, when the interchangeable lens is a cata-dioptic lens, an exposure time for a fixed aperture value of the cata-dioptric lens which time provides an appropriate exposure and indicating the fixed aperture value and the exposure time thereon.

According to another aspect of the present invention, there is provided a cata-dioptric lens, comprising means for receiving a reading signal from a body on which the cata-dioptric lens is mounted, and means for successively forwarding data peculiar to the cata-dioptric lens to the body in response to the reading signal, the data peculiar to the cata-dioptric lens including data regarding a fully open aperture value and data regarding a maximum aperture value, the two data being equal to each other.

The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.

FIG. 1 is a diagrammatic representation illustrating general construction of a exposure controlling system and an interchangeable lens according to the present invention;

FIG. 2 is a perspective view of a focus condition detecting device showing a preferred embodiment of the present invention;

FIG. 3 is a perspective view showing detailed construction of essential part of the focus condition detecting device of FIG. 2;

FIG. 4 is a diagrammatic representation illustrating a plane of an exit pupil of a photographing lens which is used with the focus condition detecting device of FIG. 2;

FIG. 5 is a diagram illustrating several constants associated with a pupil of the focus condition detecting device of FIG. 2;

FIG. 6 is a diagram illustrating an out-of-axis focus condition detecting optical system for use with the focus condition detecting device of FIG. 2;

FIG. 7 is a diagram illustrating an on-axis focus condition detecting optical system for use with the focus condition detecting device of FIG. 2;

FIG. 8 is a diagram illustrating illuminance distributions on CCD image pickup element arrays for use with the focus condition detecting device of FIG. 2;

FIG. 9 is a circuit diagram of a camera system in which the focus condition detecting device of FIG. 2 is employed; and

FIGS. 10a to 16 are flow charts illustrating operation of the camera system of FIG. 9.

Referring first to FIG. 1, there is illustrated general construction of an exposure controlling system for an interchangeable lens embodying the present invention. The exposure controlling system comprises a judging means 1 for judging, depending upon data from an interchangeable lens 11, whether or not the interchangeable lens 11 is a cata-dioptric lens ML, an exposure operating means 2 for effecting, when mounting of the cata-dioptric lens ML is not judged, exposure calculation with a data of a fully open aperture value Avo from the interchangeable lens 11 and for effecting, when mounting of the cata-dioptric lens ML is judged, the same exposure calculation as that when no interchangeable lens 11 is mounted to find only an exposure time Tv, and an exposure display means 3 for displaying thereon, when mounting of the cata-dioptric lens ML is not judged, an aperture value Av and the exposure time Tv from the exposure operating means 2 and for displaying thereon, when mounting of the cata-dioptric lens ML is judged, for exposure time Tv from the exposure operating means 2 and the open exposure value Avo from the interchangeable lens 11.

On the other hand, the interchangeable lens 11 includes the cata-dioptric lens ML, a storage means 4 in which data peculiar to the cata-dioptric lens ML are fixedly stored, a reading instruction signal receiving means 5 for receiving a reading instruction signal from a body of a camera on which the interchangeable lens 11 is mounted, and a data forwarding means 6 for successively forwarding data from the storage means 4 to the body in response to the reading instruction signal. The data stored in the storage means 4 include a fully open aperture value Avo and a maximum aperture value Avmax of the interchangeable lens 11, and here the fully open aperture value Avo and the maximum aperture value Avmax are equal to each other.

With the exposure controlling system for an interchangeable lens according to the present invention, the judging means 1 judges, depending upon data from the interchangeable lens 11, whether or not the interchangeable lens 11 mounted on the body of the camera is the cata-dioptric lens ML, and then when the cata-dioptric lens ML is mounted, exposure calculation and exposure display are effected in a different manner from that when the interchangeable lens 11 mounted is an ordinary lens. In particular, when the cata-dioptric lens ML is mounted, the exposure operating means 2 effects the same exposure calculation to that when the interchangeable lens 11 is not mounted on the camera body and thus finds out only an exposure time Tv. Then, the exposure display means 3 displays the exposure time Tv from the exposure operating means 2 and a fully open aperture value Avo from the interchangeable lens 11. To the contrary, when the interchangeable lens 11 mounted is an ordinary lens other than the cata-dioptric lens ML, the exposure operating means 2 effects exposure calculation with a data of a fully open aperture value Avo from the interchangeable lens 11, and then the exposure display means 3 displays an aperture value Av and an exposure time Tv from the exposure operating means 2. Accordingly, also when the cata-dioptric lens Ml is mounted, apparently exposure calculation is conducted and the exposure time TV and the aperture value Av are both displayed in accordance with the results of such exposure calculation. Accordingly, there is no change in manner of use of the camera comparing with that when the interchangeable lens 11 mounted is an ordinary lens.

Meanwhile, the interchangeable lens 11 includes the storage means 4 in which data peculiar to the lens are fixedly stored. In response to a reading instruction signal received at the reading instruction signal receiving means 5 from the camera body, data from the storage means 4 are successively forwarded to the camera body by the data forwarding means 6. This is a quite similar operation to that of an ordinary interchangeable lens. In addition, in the case of the interchangeable lens 11, the fully open aperture value Avo and the maximum aperture value Avmax both stored in the storage means 4 are equal to each other. Accordingly, on the side of the camera body, when it is detected that Avo=Avmax, the interchangeable lens 11 mounted is judged as a cata-dioptric lens ML.

Referring now to FIG. 2, there is shown general construction of a multi-point distance measuring module provided in a single lens reflex camera. The module shown includes a photographing lens 11, a main mirror 12, a sub mirror 14 and a focus condition detecting optical system 15. A film is placed in a plane 13 behind the sub mirror 14. The focus condition detecting optical system 15 includes a field diaphragm 22 disposed near a focal plane of the photographing lens 11 and having three rectangular openings 22a, 22b, and 22c formed therein. The focus condition detecting optical system 15 further includes three condenser lenses 21a, 21b and 21c, a module mirror 20, three separator lens pairs 18a, 18b and 18c, and three CCD (charge coupled device) image pickup element arrays 16a, 16b and 16c disposed on a focal plane 17 of the separator lenses 18a, 18b and 18c. The focus condition detecting optical system 15 further includes a diaphragm mask 19 having three pairs of circular or elliptical openings 19a, 19b and 19c formed therein. An image, the field of which has been limited by the rectangular opening 22a of the field diaphragm 22, then passes the condenser lens 21a and is then projected as two images on the CCD image pickup element array 16a by the diaphragm mask 19a and the separator lens pair 18a. Here, it is judged that when the distance between the two images is equal to a predetermined distance, the photographing lens 11 is in and in-focus condition, but when the distance is smaller or greater than the predetermined distance, the photographing lens 11 is in the forwardly or rearwardly out-of-focus condition, respectively. Images limited by the field diaphragms 22b and 22c are similarly projected to the CCD image pickup element arrays 16b and 16c by the condenser lenses 21b and 21c and the separator lens pairs 18b and 18c, respectively.

Referring now to FIG. 3, the focus condition detecting optical system 15a on an optical axis z (i.e., a combination of the condenser lens 21a, separator lens pair 18a and CCD image pickup element array 16a) and the focus condition detecting optical system 15b out of the optical axis z (a combination of the condenser lens 21b, separator lens pair 18b and CCD image pickup element array 16b) are extracted from FIG. 2. Focal point detecting frames of the focus condition detecting optical systems 15a and 15b are shown as distance measuring frames A and B on a film equivalent plane F. The distance measuring frames A and B will be hereinafter referred to as on-axis distance measuring frame and out-of-axis distance measuring frame, respectively. Meanwhile, distance measuring frames of the distance measuring frames A and B projected on a plane of an object article via the photographing lens 11 are denoted at A' and B', respectively. A pair images of the separator lens pair 18a of the on-axis focus condition detecting optical system 15a projected by the condenser lens 21a on the plane of the exit pupil of the photographing lens 11 are denoted at 11a and 11b. Another pair images of the separator lens pair 18b of the out-of-axis focus condition detecting optical system 15b projected by the condenser lens 21b on the plane of the exit pupil of the photographing lens 11 are denoted at 11c and 11d.

FIG. 4 generally illustrates positional relationships between an exit pupil opening of the photographing lens at a given position of the exit pupil of the photographing lens and areas of the exit pupil passed by AF beams of light which enters the focus condition detecting optical systems. FIGS. 5 and 6 are diagrammatic representations illustrating, among parameters appearing in FIG. 4, constants relating to the AF pupil which are determined by designing and arrangement of the focus condition detecting optical systems. In FIG. 5, the on-axis focus condition detecting optical system 15a is viewed in the direction indicated by an arrow mark x in FIG. 3, but if the out-of-axis focus condition detecting optical system 15b is viewed in the direction indicated by another arrow mark y in FIG. 3, then a similar view will be provided. FIG. 6 is a view wherein the out-of-axis focus condition detecting optical system 15b is viewed in the direction of the arrow mark X in FIG. 3.

Before entering the following description, various parameters and constants appearing in FIGS. 4 to 6 will be described.

Referring to FIG. 4, reference symbol Pz denotes an exit pupil position which is defined as a distance between the film equivalent plane F and a plane of an exit pupil of a predetermined photographing lens.

Po is a radius of an outside exit pupil at the exit pupil position Pz. The radius Po will be hereinafter referred to as exit pupil outer radius.

.DELTA.Po is a parameter with which the shape of the outside exit pupil as viewed from a predetermined image height position is to be corrected. The parameter .DELTA.Po will be hereinafter referred to as outside exit pupil image height correcting data or outside image height correcting data for short.

Po' is an exit pupil radius for restricting an inside exit pupil where the photographing lens used is of the cata-dioptric type. The exit pupil radius will be hereinafter referred to as exit pupil inner radius. Although generally the exit pupil outer radius Po and the exit pupil inner radius Po' are not always involved in the same exit pupil position, it is assumed in the following description that they are involved in the same position.

.DELTA.Po' is a parameter with which the shape of the inside exit pupil as viewed from a predetermined image height position is to be corrected. The parameter .DELTA.Po' will be hereinafter referred to as inside exit pupil image height correcting data or inside image height correcting data for short. Although generally the shape of an exit pupil is circular in most cases, it approaches an ellipse such as shown in a broken line in FIG. 4 as the image height on the plane of the film increases. .DELTA.Po and .DELTA.Po' are parameters which represent a degree of such change in shape or deformation of the exit pupil.

AFP is an area through which an AF beam of light to enter the focus condition detecting optical system passes.

Ho is an amount of displacement of an AF beam area AFP from the main optical axis z of the photographing lens. In the case of the on-axis focus condition detecting optical system 15a, the amount of displacement Ho is set to Ho=O.

ro is magnitude of an AF beam area AFP at the exit pupil position Pz.

do is a distance between two AF beam areas AFP at the exit pupil position Pz. The distance do is an amount which has an influence on the detecting sensitivity of the focus condition detecting optical system, and if the distance do increases, the focus condition detecting sensitivity also increased, but this disables use of a photographing lens having a smaller exit pupil radius.

.DELTA.d is an out-of-focus amount of an AF beam area AFP in the focus condition detecting optical system.

OUT is an outside pupil margin amount which is provided by a beam of light incident to the focus condition detecting optical system relative to the photographing lens. The outside pupil margin amount OUT is represented by a following equation:

Particularly in the case of the on-axis focus condition detecting optical system 15a, normally Ho=0 and .DELTA.Po=0. Accordingly,

IN is an inside pupil margin amount where the photographing lens used is of a cata-dioptric type and is represented by a following equation:

Particularly in the case of the on-axis focus condition detecting optical system 15a, Ho=0 and .DELTA.Po=0. Accordingly,

Depending upon the positive or negative signs of the outside and inside pupil margin amounts OUT an IN, selection of distance measuring frames and selection of distance measuring areas in a distance measuring frame, which will be hereinafter described in detail, are effected. Referring now to FIG. 5, reference symbol a denotes a distance from the condenser lens 21a to the film equivalent plane F.

t is a distance from the condenser lens 21a to the separator lens 18a or else to the diaphragm mask 19a very near to the separator lens 18a.

Ps is a position to which an image of the separator lens 18a or else the diaphragm mask 19a very near to the separator lens 18a is projected by the condenser lens 21a, and the image and the position will be hereinafter referred to as AF pupil and AF pupil position, respectively.

Os is a point on the optical axis at the AF pupil position Pa, and QsQs' is an AF pupil opening at the AF pupil position.

The AF pupil position Ps and the Af pupil opening QsQs' are uniquely determined specifically from the power of the condenser lens 21a and the aforementioned distances a and t. Accordingly, the distances QsQs' and OsQs from the point Os on the optical axis to the farthest and nearest points Qs and Qs', respectively, of the AF pupil opening QsQs' can be regarded as constants. Further, the magnitude e of a distance measuring frame on the film equivalent plane F and the inclination .omega. of a main beam of light in the on-axis focus condition detecting optical system 15a with respect to the main optical axis z of the photographing lens are also determined specifically.

By the way, the out-of-focus amount .DELTA.d of an AF beam area AFP described hereinabove with reference to FIG. 4 is .DELTA.d>0 when the exit pupil position is farther or nearer than the conjugate position of the separator lens or the diaphragm mask determined in advance for the focus condition detecting optical system. This will described with reference to FIG. 5. Beams of light will be examined successively which pass the exit pupil of the photographing lens from the separator lens 18a past the condenser lens 21a. In the case of the exit pupil position Pz is Pz=Ps, beams of light indicated by a long and short dash chain line, a solid line and a broken line going from the central point Ro of the separator lens 18a pass a single point Rs=Rs', and the out-of-focus amount .DELTA.d is .DELTA.d=0. When the exit pupil position Pz of the photographing lens is smaller than the AF pupil position Ps (that is, Pz=Pz.sub.1 <Ps), the beam of light indicated by a solid line going from the central point Ro of the separator lens 18a passes a point R.sub.1, and the beam of light indicated by a broken line passes another point R.sub.1 ' while the beam of light indicated by a long and short dash chain line passes an intermediate point between the two points R.sub.1 and R.sub.1 ', and here the out-of-focus amount .DELTA.d>0. When the exit pupil position Pz of the photographing lens is positioned farther than the AF pupil position Ps (that is, Pz=Pz.sub.2 >Ps), the beam of light indicated by a solid line going from the central point Ro of the separator lens 18a passes a point R.sub.2 ', and the beam of light indicated by a broken line passes another point R.sub.2 while the beam of light indicated by a long and short dash chain line passes an intermediate point between the two points R.sub.2 ' and R.sub.2, and also the out-of-focus amount .DELTA.d is .DELTA.d>0 here. It is to be noted that while it is assumed here that the AF beam restricting mask (diaphragm mask) of the focus condition detecting optical system is circular in order to represent relationships of various parameters in a simple manner, generally it need not be circular.

Referring now to FIG. 6, .theta. is an inclination of a main beam of light lp with respect to the main optical axis z in the out-of-axis focus condition detecting optical system 15b, and h is an amount of displacement of an out-of-axis distance measuring frame from the main optical axis z. The parameters .theta. and h are also determined specifically by a geometrical arrangement of the CCD image pickup element array 16b, separator lens 18b (and diaphragm mask 19b very near to the separator lens 18b) and the condenser lens 21b. Accordingly, once designing of the camera body is completed, then the parameters .theta. and h will thereafter remain unique constants.

The parameters Ho, ro and do described hereinabove with reference to FIG. 4 are represented as follows using the parameters mentioned above.

In particular, at first the amount Ho of displacement of an AF beam area AFP from the main optical axis z of the photographing lens is represented as

Here, the amount h of displacement of the distance measuring frame from the main optical axis z, the distance a from the condenser lens 21a to the film equivalent plane F and the inclination .theta. of the main beam lp of light with respect to the main optical axis z are all information regarding the body of the camera and thus constants as described hereinabove. To the contrary, the exit pupil position Pz is information regarding a lens and may be different for each of lenses.

The magnitude ro of an AF beam area AFP at the exit pupil position Pz is represented as

Here, O is the point on the optical axis at the exit pupil position Pz, and Q is a point of the AF beam area AFP farthest from the optical axis at the exit pupil position Pz while Q' is a point of the AF beam area AFP nearest to the optical axis at the exit pupil position Pz.

When PZ=Pz.sub.1 .ltoreq.Ps, referring to FIG. 5, ##EQU1##

To the contrary, when Pz=Pz.sub.2 >Ps, referring to FIG. 5, ##EQU2##

Further, the distance do between the two AF beam areas AFP is represented as ##EQU3##

In the equations above, OsQs, OsQs', and Ps and e are all body constants and hence constant. To the contrary, Pz=Pz.sub.1 and Pz.sub.2 are values peculiar to individual lenses.

As apparent from the matters described above, the outside and inside pupil margin amounts OUT and IN are written by way of the body constants OsQs, OsQs', Ps and e and the lens information Pz, Po, Po', .DELTA.Po and .DELTA.Po'. If suitable threshold values are provided for the outside and inside pupil margin amounts OUT and IN, selection of distance measuring zones in on-axis and out-of-axis distance measuring frames or selection of a distance measuring frame where there are a plurality of distance measuring frames can be effected. For selection of a distance measuring zone or a distance measuring frame, there are two available methods including a method of calculating, in a camera body, the outside and inside pupil margin amounts OUT and IN using the equations specified as above and another method of preparing, in a camera body, a table for setting suitable threshold values for Pz, Po, Po', Po and Po' based on the results calculated in advance to select a distance measuring zone. In the following description, however, the latter method is adopted.

At first, an example of selection of a distance measuring area in a distance measuring frame on the optical axis will be described.

FIG. 7 illustrates various ecliptical conditions of AF beams of light in the on-axis focus condition detecting optical system 15a for various photographing lenses having exit pupil Poa, Poa'; Pob, Pob'; Poc, Poc'; and Pod, Pod'. Here, it is assured that the exit pupils Pob and Pob' correspond to the AF pupil opening QsQs' in FIG. 5. An image AoBo on the film equivalent plane F is formed as images A.sub.1 B.sub.1 and A.sub.2 B.sub.2 on the CCD image pickup element arrays by the condenser lens 21a and the separator lenses 18a.sub.1 and 18a.sub.2, respectively. If passing areas of light incident to the points A.sub.1, B.sub.1, A.sub.2 and B.sub.2 on the CCD image pickup element arrays are examined, it can be found that light incident to the point A.sub.1 passes a passing area LA1 to UA1; light incident to the point B.sub.1 passes another passing LB1 to UB1; light incident to the point A.sub.2 passes a further passing area LA2 to UA2; and light incident to the point B.sub.2 passes another passing area LB2 to UB2. In the case of the exit pupil Pob and Pob' which correspond to the AF pupil opening QsQs' of FIG. 5, naturally no eclipse will appear in an AF beam of light.

FIG. 8 illustrates illuminance distributions of a plane of the elements of the CCD image pickup element arrays corresponding to the exit pupil Poa, Poa'; Pob, Pob'; Poc, Poc'; and Pod, Pod'. Referring to FIG. 8, the axis of abscissa represents the direction in which the elements of each of the CCD image pickup element arrays is arranged while the axis of ordinate represents the illuminance on each of the planes of the elements. It is assumed that an image A.sub.1 B.sub.1 is formed on the right-hand side image pickup element array R while an image A.sub.2 B.sub.2 is formed on the left-hand side image pickup element array L. The left-hand side image pickup element array L is divided into four distance measuring areas I to IV.

Where a photographing lens having the exit pupils Pob and Pob' is used, no eclipse will be caused in an AF beam of light either by the outside Pob or the inside Pob' of the exit pupils Pob and Pob', and consequently, a uniform element plane illuminance distribution E is obtained. Accordingly, all of the distance measuring areas I to IV can be used.

Where a photographing lens having the exit pupils Poa and Poa' is used, eclipses will be caused in a beam of light at UA2 and a beam of light at UB1 by the outside exit pupil Poa. Consequently, the illuminance on the plane of the elements near the optical axis z is decreased such as shown by the distribution J. Further, since eclipses will be caused in a beam of light at LB2 and a beam of light at LA1 by the inside exit pupil Poa', the illuminance on the plane of the elements remote from the optical axis z is also decreased such as shown by the distribution G. Accordingly, the distance measuring area IV can be used without being influenced by eclipses of AF beams of light.

Where a photographing lens having the exit pupils Poc and Poc' is used, eclipses will be caused in a beam of light at UB2 and a beam of light at UA1 by the outside exit pupil Poc. Consequently, the illuminance on the plane of the elements remote from the optical axis z is decreased such as shown by the distribution G. Further, since eclipses will be caused in a beam of light at LA2 and a beam of light at LB1 by the inside exit pupil Poc', the illuminance on the plane of the elements near the optical axis z is also decreased such as shown by the distribution J. Accordingly, the distance measuring area IV can be used without being influenced by eclipses of AF beams of light.

Where a photographing lens having the exit pupils Pod and Pod' is used, great eclipses will be caused in a beam of light at UB2 and a beam of light at UA1 by the outside exit pupil Pod. Consequently, the illuminance on the plane of the elements remote from the optical axis z is decreased significantly such as shown by the distribution H. Accordingly, the distance measuring areas I, II and IV cannot be used. Further, since eclipses will be caused in a beam of light at LA2 and a beam of light at LB1 by the inside exit pupil Pod', the illuminance on the plane of the elements near the optical axis z is also decreased such as shown by the distribution J. Accordingly, the distance measuring area III cannot be used either. After all, no distance measuring area can be used in this instance.

Such tables as Table 1 to Table 4 below are produced from the facts described above.

Table 1 above indicates an example of selection table for distance measuring areas in an on-axis distance measuring frame from an exit pupil position Pz and an exit pupil outer radius Po. In Table 1, I, II, III and IV denote distance measuring areas. The mark x represents that measurement of the focus condition is impossible because the eclipse of the illuminance distribution is too great. Po.sub.1 to Po.sub.4 and Pz.sub.1 to Pz.sub.4 denote predetermined constants calculated from the equations appearing hereinabove. The exit pupil Pob described hereinabove corresponds to the conditions of Pz=Ps and Pob=OsQs; the exit pupil Poa corresponds to the conditions of Pz.sub.3 <Pz<Pz.sub.4 and Po.sub.3 <Poa<Po.sub.4 ; the exit pupil Poc corresponds to the conditions of Pz.sub.1 <Pz<Pz.sub.2 and Po.sub.1 <Poc<Po.sub.2 ; and the exit pupil Pod corresponds to the conditions of Pz<Pz.sub.1 and Pod<Po.sub.1. Selection of distance measuring areas in the case of a photographing lens of the non-exit pupil type can be attained using Table 1.

Meanwhile, Table 2 indicates an example of selection table for distance measuring areas in an on-axis distance measuring frame from an exit pupil position Pz and an exit pupil inner radius Po'. The exit pupil Pob' described hereinabove corresponds to the conditions of Pz=Ps and Pob'=OsQs'; the exit pupil Poa' corresponds to the conditions of Pz.sub.3 <Pz<Pz.sub.4 and Po.sub.3 '<Poa'<Po.sub.4 '; the exit pupil Poc' corresponds to the conditions of Pz.sub.1 <Pz<Pz.sub.2 and Po.sub.1 '<Poc'<Po.sub.2 '; and the exit pupil Pod' corresponds to the conditions of Pz<Pz.sub.1 and Pod'<Po.sub.1 '. In the case of a photographing lens of the cata-dioptric type, at first selection of distance measuring areas is effected, at a predetermined exit pupil position Pz, from the exit pupil outer radius Po using Table 1 above, and then selection of distance areas is effected from the exit pupil inner radius Po' using Table 2, whereafter a distance measuring area common to the selected distance areas is finally determined.

Table 3 above indicates an example of selection table for distance measuring areas in an out-of-axis distance measuring frame from an exit pupil position Pz and a deformed exit pupil outer radius Po. The deformed exit pupil outer radius Po is determined approximately from the exit pupil outer radius Po as viewed from a position on or near the optical axis, the outside image height correcting data .DELTA.Po and the body constant k relating to the exit pupil position Pz in accordance with a following expression:

Here, if it is assumed that in FIG. 6 the position at which the main beam lp of the AF beam of light intersects the optical axis z is substantially Pz=Ps (AF pupil position, a constant), k is k=0 near Pz=Ps, which represents that the AF beam of light is not displaced with respect to the main optical axis z, and at a position at which an eclipse most possibly appears, there is no influence of .DELTA.Po (refer to FIG. 4). Further, when Pz<<Ps or Pz>>Ps, k approaches 1.

Since generally an AF beam area AFP of an out-of-axis distance measuring area is displaced from the optical axis z, k is a parameter which varies from k=0 to 0.8 or so. The signification of the value k itself is a coefficient with which weighting of .DELTA.Po is to be changed when the marginal degrees of the AF beam area AFP of the out-of-axis focus condition detecting optical system and the exit pupil outer radius Po at an exit pupil position Pz far different from the AF pupil position Ps are to be considered.

The deformed exit pupil outer radius Po defined in this manner is utilized for judgment of a distance measuring area only in an out-of-axis distance measuring frame. An example of the same is shown in Table 3. The differences from the selection of distance measuring areas in an on-axis distance measuring frame indicated in Table 1 are:

(1) that, in the case of a photographing lens wherein the exit pupil position Pz is small, an eclipse will readily appear in an AF beam of light even if the deformed exit pupil outer radius Po is large; and

(2) that, also in a photographing lens wherein the exit pupil position Pz is displaced by a great distance from the AF pupil position Ps, an eclipse will readily appear in the AF beam of light because the AF beam of light is displaced to a great extent from the optical axis as seen in FIG. 6 and also because the value k itself increases.

Similar arguments will be approved for the exit pupil inner radius Po' for selecting an out-of-axis distance measuring area if the deformed exit pupil inner radius Po' is defined as Po'=Po'=k'.multidot..DELTA.Po' (0.ltoreq.k'.ltoreq.1) and Po mentioned hereinabove is replaced by the Po'. FIG. 4 indicates an example of selection table for distance measuring areas in and out-of-axis distance measuring frame from an exit pupil position Pz and a deformed exit pupil inner radius Po'.

FIG. 9 is a circuit diagram of a camera system to which the present invention is applied. The camera system includes a focus condition detecting light receiving device DT having three CCD image pickup element arrays 16a, 16b and 16c shown in FIG. 2. The camera system further includes an interface circuit IFC for controlling operation of the CCD image pickup element arrays of the focus condition detecting light receiving device DT. The interface circuit IFC has a function of converting analog signals read from the CCD image pickup element arrays into digital signals and transmitting the thus converted digital signals to a microcomputer COM via a data bus DBAF, and another function of transmitting completion of a charge accumulating operation of the CCD image pickup element arrays to an interrupt input terminal INT.sub.1 of the microcomputer COM. It is to be noted that the charge accumulating time to the CCD image pickup element arrays is controlled by an output of another light receiving means not shown for monitoring the brightness of an object.

The camera system further includes a lens feeding motor MOAF for automatic focusing, and a motor controlling circuit MDA which receives signals from output ports p.sub.0 and p.sub.1 of the microcomputer COM and controls the lens driving motor MOAF to rotate forwardly or reversely or be braked or stopped. The camera system includes a display device DPA which receives signals from output ports p.sub.2 and p.sub.3 of the microcomputer COM and makes an indication of a moving direction of the lens and an indication of a focus condition or a warning that detection of a focus condition is impossible.

The camera system further includes an encoder ENL for producing pulses with which the amount of the lens fed by the lens driving motor MOAF (amount of rotation of the motor) is to be monitored, and another encoder ENAP for producing pulses with which the aperture value of the lens is to be monitored. A data selector SEC delivers pulses from the AF encoder ENL when an output port p.sub.4 of the microcomputer COM is at a "Low" voltage level, but delivers pulses from the aperture encoder ENAP when the output port p.sub.4 is at a "High" voltage level, to an input terminal CNTR of the microcomputer COM for an event counter. The event counter is provided within the microcomputer COM. A data is preset to the event counter, and each time a pulse is delivered to the terminal CNTR, the contents of the event counter are decremented by one, and when the contents are reduced to zero, an interruption takes place at the microcomputer COM.

A light measuring switch S.sub.1 is closed when a release button is depressed to a first depth or position, and the closing signal of the light measuring switch S.sub.1 is delivered to another interrupt input terminal INT.sub.0 and input port p.sub.5 of the microcomputer COM. A release switch S.sub.2 is closed when the release button is depressed to a second deeper position. The closing signal of the release switch S.sub.2 is delivered to an input port p.sub.6 of the microcomputer COM. A reset switch S.sub.3 is closed upon completion of an exposure controlling operation and is opened upon completion of winding or charging of a film. The closing signal of the reset switch S.sub.3 is delivered to an input port p.sub.7 of the microcomputer COM.

A power source circuit GV operates when a power source controlling a signal PWC delivered from an output port p.sub.8 of the microcomputer COM is at the "Low" level. The power source circuit GV delivers a high voltage HV and a low voltage LV from an output power of power source batteries BA. The high voltage HV makes a power source to the light receiving device DT and the interface circuit IFC. Meanwhile, the low voltage LV makes a power source to the aforementioned display device DPA, encoders ENL and ENAP, data selector SEC, and a film sensitivity reading circuit ISD, a lens circuit LEC, a light measuring and analog to digital converting circuit MEC and a decoder driver DDR which will be hereinafter described. To the contrary, the motor controlling circuits MDA and MDF, display device DSP and microcomputer COM receive supply of a power directly from the power source batteries BA over a power source line EV.

The film sensitivity reading circuit ISD reads an ISO data indicative of a sensitivity of the film on a film container and delivers the film sensitivity data serially to a serial input terminal SIN of the microcomputer COM in synchronism with serial clocks SCK from the microcomputer COM when a film sensitivity reading circuit selecting signal CSIS from an output port P.sub.9 of the microcomputer COM is charged to the "Low" level. The lens circuit LEC is provided in an interchangeable lens and has such a circuit construction as, for example, disclosed in Japanese Patent Laid-Open No. 59-140408. When a lens circuit selecting signal CSL from an output port p.sub.10 is charged to the "Low" level, various data stored in a ROM (read only memory) in the lens circuit LEC are transmitted serially to the serial input terminal SIN in synchronism with the serial clocks SCK. Here, the data fixedly stored in the ROM in the lens circuit LEC will be described separately for a fixed focal length lens and a zoom lens.

Table 5 and Table 6 indicate stored contents of ROMs built in lenses in the case of a fixed focal length lens and a zoom lens, respectively. A data common to all of the lenses is fixedly stored as a mounting signal ICP at a location of the address 01 of the ROM. At locations of the addresses 02 and 03, a fully open aperture value Avo and a maximum aperture value Avmax are stored fixed, respectively. In the case of a zoom lens wherein the aperture value is varied by zooming, such aperture values at the shortest focal length are fixedly stored at the locations. Meanwhile, in the case of a cata-dioptric lens, Avo=Avmax because the aperture is fixed. A data of the focal length f is stored at a location of the address 04 in the case of a fixed focal length lens, and data of the focal lengths f are stored at locations of the addresses 10 to 1F. It is to be noted that the lower 4 bits 0 to F of the addresses equal to or higher than 10 in the case of a zoom lens are specified by a signal obtained from zoom encoder upon zooming. At a location or locations of the address 05 or addresses 20 to 2F, a coefficient or coefficients K with which a defocus amount is to be converted into a driving amount of the lens driving motor MOAF are stored. At a location or locations of the address 06 or addresses 30 to 3F, a data or data of a changing amount or amounts .DELTA.Av of the aperture value of the zoom lens changed upon zooming are stored, and in the case of a fixed focal length lens, .DELTA.Av=0. At a location or locations of the address 07 or addresses 40 to 4F, a data or data of an exit pupil position Pz are stored while a data or data of an exit pupil outer radius Po are stored at a location or locations of the address 08 of addresses 50 to 5F. At a location of the address 09, a data of an exit pupil inner radius Po' is stored, and in the case of a lens other than a cata-dioptric lens, Po'=0. An outside image height correcting data or data .DELTA.Po are stored at a location or locations of the address 0A or addresses 60 to 6F while an inside image height correcting data .DELTA.Po' is stored at a location of the address 0B. In the case of a lens other than a cata-dioptric lens, the inside image height correcting data .DELTA.Po' is .DELTA.Po'=0.

The display circuit DSP makes an indication of display data transmitted from the microcomputer COM. The light measuring and analog to digital converting circuit MEC operates its light measuring operation when supply of power of the low voltage LV from the power source circuit GV is started, and then when an analog to digital conversion enabling signal ADEN from an output port p.sub.12 of the microcomputer COM is changed to the "Low" level, analog to digital conversion is repeated at a predetermined cycle. Then, when a light measuring and analog to digital converting circuit selecting signal CSME from an output port p.sub.11 is changed to the "Low" level, digital data latched are delivered to the microcomputer COM in synchronism with serial clocks SCK. A load driving circuit DDR decodes a data transmitted thereto from the microcomputer COM over a data bus DBDR and drives loads in accordance with the decoded results. The loads may include a release magnet RLM, an aperture controlling magnet APM, a leading screen controlling magnet 1CM, a trailing screen controlling magnet 2CM, a motor MOCH for feeding a film and for charging an exposure controlling mechanism, and a driver MDF for the motor MOCH. The camera system further includes an oscillator X.

Operation of the camera system will be described below with reference to flow charts of FIGS. 10a to 16. In the following description, the mark "#" denotes a number of a step of a program of the microcomputer COM.

If the release button is operated, the light measuring switch S.sub.1 is closed when the release button is moved to its first position. Thereupon, an interrupt signal is received at the interrupt input terminal INT.sub.0 of the microcomputer COM. Consequently, the microcomputer COM starts its operation from an interrupt routine INT.sub.0 illustrated in FIG. 10a. Referring to FIG. 10a, the microcomputer COM changes, at first at step #1, the power source controlling signal PWC to be delivered from the output port p.sub.8 thereof to the "Low" level to render the power source circuit GV operative. Then, at step #2, the microcomputer COM outputs reference clocks CKOUT to the interface circuit IFC, display circuit DSP and light measuring and analog to digital converting circuit MEC, and then executes, at step #3, initialization of the CCDs of the image pickup element arrays to sweep out the charge accumulated in the CCDs. Subsequently, a charge accumulating operation of the CCDs is started at step #4, and upon completion of the charge accumulating operation, reception of an interrupt signal at the interrupt input terminal INT.sub.1 is enabled at step #5, whereafter the analog to digital conversion enabling signal ADEN from the output port p.sub.12 is charged to the "Low" level to allow conversion of a measured light value from an analog to a digital value at step #6.

Subsequently, a light measuring routine is executed. In the light measuring routine, a lens data and a film sensitivity data (ISO data) are first read in from an interchangeable lens and a film container at steps #7 and #8, respectively. After then, states of flags IFF.sub.1 and IFF.sub.2 are discriminated at steps #9 and #10. The flag IFF.sub.1 is set to "1" when an in-focus condition is reached, and the other flag IFF.sub.2 is set when a light measuring data is fetched into the microcomputer COM after an in-focus condition has been reached. Accordingly, either when an in-focus condition is not yet reached or when a measured light data is not yet fetched in whereas an in-focus condition is already reached, the measured light data is fetched in at step #11, and then in case the data is fetched in after an in-focus condition has been reached (step #12), the flag IFF.sub.2 is set to "1" at step #13 whereafter the sequence advances to a calculation routine. To the contrary, when the flags IFF.sub.1 and IFF.sub.2 are both "1" at steps #9 and #10, respectively, then the microcomputer COM advances the sequence directly to the calculation routine without receiving input of a measured light data.

The calculation routine is illustrated in FIG. 10b. In the calculation routine, the microcomputer COM judges at first at step #14, whether or not a mounted lens signal ICP is received, and when a mounted lens signal ICP is received, the sequence advances to step #15, but when no mounted lens signal ICP is received, the sequence advances to step #16. At step #15, it is judged whether or not the fully open aperture value Avo is equal to the maximum aperture value Avmax (Avo=Avmax). If the lens mounted on the camera is a cata-dioptric lens, then Avo=Avmax, and the sequence thus advances to step #16, but otherwise when Av.noteq.Avmax, this means that the mounted lens is an ordinary interchangeable lens or an ordinary dioptric lens and the sequence thus advances to step #19. When no lens is mounted or when a cata-dioptric lens is mounted, aperture control is naturally impossible and hence the aperture must be considered fixed. Thus, at step #16, an ISO value Sv indicative of a sensitivity of a film is added to a measured light data=Bv-Av (Bv is a brightness of an object, and Av is a fixed aperture value) to find an exposure time Tv. Then at step #17, it is judged whether or not there is a lens mounted on the camera, and if no lens is mounted, then the exposure time is displayed while the F-number is displayed as a warning pattern (for example, "--") at step #18. To the contrary, when it is judged at step #17 that a lens is mounted, the lens here is a cata-dioptric lens, and accordingly at step #21, the calculated exposure time Tv and the fixed aperture value (fully open aperture value Avo=maximum aperture value Avmax). In case it is judged at step #15 that the lens mounted is not a cata-dioptric lens, then Avo+.DELTA.Av+Sv is added to the measured light data=Bv-(Avo+.DELTA.Av) to find an exposure value Ev at step #19. After then, at step #20, a programmed exposure calculation is executed based on the exposure value Ev to find an aperture value Av and an exposure time Tv, whereafter the aperture value Av and the exposure time Tv are displayed at step #21.

After completion of the operation described above, a flag AEF is set to "1" at step #22. The flag AEF is a flag which is set to "1" if an exposure calculation is completed. Then, a flag CF is checked at step #23, and then if the flag CF is CF=1, then the sequence advances to an AF routine illustrated in FIG. 11b. The flag CF is provided to advance the sequence from step #23 to the AF routine after the remaining exposure calculation after data from the CCD has been fetched into the microcomputer COM at once if an exposure calculation is not yet completed upon completion of a charge accumulating operation of the CCDs during operation of the light measuring routine or the calculation routine.

In case the flag CF is not CF=1 at step #23, then the sequence advances to step #24 at which it is judged whether or not the release switch S.sub.2 is closed and then to step #25 at which it is judged whether or not an exposure controlling value has been calculated from a measured light data after reaching of an in-focus condition. In case the conditions are met at both steps #24 and #25, the sequence advances to an exposure controlling routine illustrated in FIGS. 12a and 12b in order to effect an exposure controlling operation.

To the contrary, if either one of the conditions is met at step #24 or #25, then it is judged at step #251 whether or not the light measuring switch S.sub.1 is in a closed condition, and if the light measuring switch S.sub.1 is in a closed condition, then the sequence returns to the light measuring routine beginning with step #7 described above, but on the contrary if the light measuring switch S.sub.1 is not in a closed condition, then a following stop routine illustrated in FIG. 10c is executed.

Referring to FIG. 10c, in the stop routine, all flags are reset at first at step #26, and then the output port p.sub.4 of the microcomputer COM is changed to the "Low" level at step #27, whereafter a data to render the display device ineffective so that it may display nothing thereon is transmitted to the display circuit DSP at step #28. Subsequently, the motor MOAF is stopped at step #29 and then delivery of the reference clocks CKOUT is stopped at step #30 whereafter the power source circuit GV is rendered inoperative at step #31. After then, the signal ADEN is changed to the "High" level to disable analog to digital conversion at step #32, and finally the microcomputer COM stops its operation.

Referring now to FIGS. 11a to 11c, operation of the AF routine will be described. Upon completion of the charge accumulating operation of the CCDs, an interrupt input signal is received at the interrupt input terminal INT.sub.1 of the microcomputer COM from the interface circuit IFC. In response to the interrupt input signal, the microcomputer COM starts its operation of the interrupt routine INT.sub.1 beginning with step #39. At first at step #39, it is judged whether or not an interchangeable lens is mounted on the camera, and if the judgment is in the affirmative, the sequence advances to step #40, but on the contrary the judgment is in the negative, the sequence jumps to step #51 of the AF routine of FIG. 11b without executing operations of fetching data from the CCDs into the microcomputer COM, detecting a focus condition or feeding the lens. At step #40, analog signals delivered from the light receiving device DT corresponding to the three arrays of CCDs are converted successively into digital signals at the interface circuit IFC and then fetched into the microcomputer COM. Then at step #41, the flag CF is set to "1", and then at step #42, it is judged whether or not the flag AEF is set to "1". Here, if the flag AEF is "0", this means that the light measuring routine and the calculation routine for the first time are not yet completed. Accordingly, the sequence returns to the step of the return address, that is, the step from which the interrupt routine INT.sub.1 is entered. Then, after the light measuring routine and the calculation routine of FIGS. 10a and 10b are completed subsequently, CF=1 is determined at step #23 and consequently the sequence now advances to the AF routine which is illustrated in FIG. 11b and begins with step #43. To the contrary, if AEF=1 is determined at step #42, then the sequence advances directly to the AF routine thus directly after completion of taking in of data of the CCDs.

Referring to FIG. 11b, in the AF routine, at first the flag CF is reset to "0" at step #43, and then the sequence advances to a subroutine SUB1 illustrated in FIG. 13. In the subroutine SUB1, distance measuring areas in which a focus condition can be detected in an on-axis distance measuring frame A are selected based on an exit pupil position Pz and a exit pupil outer radius Po. Then, at step #44, a deformed exit pupil outer radius Po for out-of-axis distance measuring frames B and C is calculated from the exit pupil outer radius Po and the outside image height correcting data .DELTA.Po both from the lens and the constant k of the camera body. Subsequently, the sequence advances to a subroutine SUB2 illustrated in FIG. 14 in which distance measuring areas in which a focus condition can be detected in the out-of-axis distance measuring frames B and C are selected based on the exit pupil position Pz and the deformed exit pupil outer radius Po. After then, at step #45, it is judged whether or not the exit pupil inner radius Po' is Po'=0, and in case Po'=0, the lens is an ordinary lens and accordingly the sequence advances directly to step #47. On the contrary, in case Po'.noteq.0 at step #45, the lens is a cata-dioptric lens and the sequence thus advances to a subroutine SUB3 illustrated in FIG. 15. In the subroutine SUB3, distance measuring areas in which a focus condition can be detected in the on-axis distance measuring frame A are selected based on the data of the exit pupil position Pz and the data of the exit pupil inner radius Po', and thus distance measuring areas which have been selected in the subroutine SUB1 and are selected also in the subroutine SUB3 are finally decided. Subsequently, at step #46, a deformed exit pupil inner radius Po' is calculated from the exit pupil inner radius Po' and the inside image height correcting data .DELTA.Po' both from the lens and the constant k' of the camera body. After then, the sequence advances to a subroutine SUB4 illustrated in FIG. 16 wherein distance measuring areas in which a focus condition can be detected in the out-of-axis distance measuring frames B and C are selected from the exit pupil position Pz and the deformed exit pupil inner radius Po' and then distance measuring areas which have been selected in the subroutine SUB2 and are also selected in the subroutine SUB4 are decided finally. After then, the sequence advances to step #47.

At step #47, it is judged whether or not there is a distance measuring area selected based on the data Pz, Po, Po', Po and Po' regarding the exit pupil, and if there is no distance measuring area selected, the sequence advances to step #51 without executing detection of a focus condition. To the contrary, in case there is at least one distance measuring area selected, detection of a focus condition (detection of a defocus amount) is executed, at step #48, for each of the selected distance measuring areas. Then at step #49, it is judged whether a reliable data has been obtained for each of the distance measuring areas, and those of the distance measuring areas for which a reliable data has not been obtained are removed. Then, it is judged at step #50 whether or not there remains at least one distance measuring area for which a reliable data has been obtained, and when there remains no reliable area, that is, when there is no reliable data, the sequence advances to step #51. At step #51, the flag IFF.sub.2 is set to"1" in order than an exposure controlling operation may be enabled whether an in-focus condition is reached or not when detection of a focus condition is impossible. Then at step #52, the display device is caused to make an indication that detection of a focus condition is impossible, whereafter a charge accumulating operation of the CCDs is started at step #53. After then, interruption at the interrupt input INT.sub.1 is enabled, and then the sequence returns to the step of the return address in the light measuring routine or the calculation routine.

If it is determined at step #50 that there is at least one reliable data, then the sequence advances to step #60 illustrated in FIG. 11c. Referring now to FIG. 11c, statistic processing is executed at step #60. The statistic processing may include, for example, adoption of a signal for the rearmost focusing or adoption of such a defocus amount that, when a plurality of data are within a predetermined defocus amount, the plurality of objects may fall in the depth of focus. Then, it is judged at step #61 whether or not the defocus amount which has been determined in the statistic processing is within an in-focus region, and in case the defocus amount is not within the in-focus region, the sequence advances to step #62, but otherwise if the defocus amount is within the in-focus region, then the sequence advances to step #70. At step #62, the direction of the defocus is displayed, and then at step #63, the defocus amount is multiplied by a converting coefficient K to find an amount of the lens feeding motor MOAF to be driven. The amount to be driven is preset to the event counter EVC at step #64. Then, interruption of the event counter is enabled at step #65, and then the lens driving motor MOAF is rendered operative at step # 66. Finally, the sequence returns to the step of the return address in the light measuring routine or the calculation routine. After then, the light measuring routine and the calculation routine are repeated while feeding the lens. During the cycles, pulses from the encoder ENL with which the amount of the lens being fed is to be monitored are delivered to the event counter via the selector SEC and the terminal CNTR of the microcomputer COM so that the contents of the event counter EVC are decremented successively.

If the contents of the event counter EVC are reduced to "0", then operation of the microcomputer COM is interrupted by the event counter (EVC interrupt). Consequently, the microcomputer COM executes the EVC interrupt routine of FIG. 12c beginning with step #100. At step #100, it is judged whether or not the camera is proceeding an AF operation. Since here the camera is proceeding an AF operation, the sequence advances to step #101 at which the motor MOAF is stopped and then to step #102 at which a charge accumulating operation of the CCDs is started in order to subsequently permit detection of a focus condition for confirmation. Then, interruption at the interrupt input terminal INT.sub.1 is enabled at step #103, whereafter the sequence enters the light measuring routine of FIG. 10a beginning with step #7. It is to be noted that the step #104 in the EVC interruption routine will be hereinafter described.

If it is judged at step #61 in the flow chart of FIG. 11c that an in-focus condition is reached, the sequence advances to step #70 at which the display device makes an indication of such an in-focus condition. Then at step #71, the flag IFF.sub.1 is set to "1", and then the sequence enters the light measuring routine beginning with the step #7. Accordingly, once an in-focus condition is confirmed, neither detection of a focus condition nor actuation of the lens will thereafter be effected so far as the light measuring switch S.sub.1 remains in a closed condition.

If it is judged at step #24 that the release switch S.sub.2 is closed and then judged at step #25 that the flag IFF.sub.2 is set to "1", the sequence enters the exposure controlling routine illustrated in FIGS. 12a and 12b. Referring firs to FIG. 12a, in the exposure controlling routine, at first the AF indication is turned off at step #75, and then at step #76, the release magnet RLM is energized to start operation of the exposure controlling mechanism. Then, it is judged at step #77 whether or not there is an interchangeable lens mounted on the camera and successively at step #78 whether or not the interchangeable lens, if mounted, is a cata-dioptric lens. In case it is judged that no lens is mounted or a cata-dioptric lens is mounted on the camera, the sequence jumps to step #83 shown in FIG. 12b without making a stopping down controlling operation. To the contrary, if an ordinary lens is mounted on the camera, then the sequence advances from step #78 to step #79 at which it is judged whether or not the controlling aperture value Av is equal to the fully open aperture value Avo, and if Av=Avo, then the sequence jumps similarly to step #83. To the contrary, if AV.noteq.Avo, then the number of steps to be stopped down (Av-Avo) is set to the event counter EVC at step #80, and then at step #81, the port p.sub.4 of the microcomputer COM is charged to the "High" level to allow pulses from the encoder ENAP, with which the amount to be stopped down is to be monitored, to be delivered from the selector SEC. After then, interruption by the timer is enabled at step #82. Referring now to FIG. 12b, the timer is started subsequently at step #83, and then at step #84, the microcomputer COM waits for a predetermined period of time. During the predetermined period of time, a stopping down operation is performed, and if operation of the microcomputer COM is interrupted by the event counter EVC, then the sequence thus enters the EVC interrupt routine of FIG. 12c. Thus, in the EVC interrupt routine, the stopping down magnet APM is rendered operative at step #104 to stop the stopping down operation. Then, since upward movement of the main mirror has been completed when the predetermined period of time elapses at step #84, the leading screen magnet 1CM is rendered operative at step #85 to start movement of the leading screen, and then the exposure time is counted at step #86. When the counting of the exposure time comes to an end, the trailing screen 2 CM is rendered operative to start movement of the trailing screen at step #87. Then at step #88, the microcomputer COM waits until the movement of the trailing screen is completed and the reset switch S.sub.3 is turned on. After turning on of the reset switch S.sub.3, the charging motor MOCH is rendered operative at step #89 to effect winding of a film and charging of the exposure controlling mechanism, and then the microcomputer COM waits at step #90 until the film winding operation and the charging operation are completed and the reset switch S.sub.3 is turned off. After turning off of the reset switch S.sub.3, the microcomputer COM waits at step #91 until a finger of an operator is released from the release button and the light measuring switch S.sub.1 is turned off. After turning off of the light measuring switch S.sub.1, the microcomputer COM enters the stop routine of FIG. 10c. Consequently, the microcomputer COM stops its operation until the light measuring switch S.sub.1 is subsequently turned on.

The subroutines SUB1, SUB2, SUB3 and SUB4 shown in FIG. 11b are illustrated in detail in FIGS. 13, 14, 15 and 16, respectively. In the subroutine SUB1 of FIG. 13, a distance measuring area of areas are selected from within the on-axis distance measuring frame A depending upon an exit pupil position Pz and an exit pupil outer radius Po in accordance with Table 1. Referring to FIG. 13, at first at step #110, Po<Po.sub.1 is judged, and in case Po<Po.sub.1, this means that there is no distance measuring frame in which a focus condition can be detected, and the sequence thus jumps to step #128. To the contrary, in case Po.ltoreq.Po.sub.1, Po>Po.sub.2 is judged subsequently at step #111, and in case Po.sub.2 >Po.gtoreq.Po.sub.1, then Y.sub.11 is set into an address register Y.sub.1i at step #112. Similarly, in case Po.sub.3 >Po.gtoreq.Po.sub.2 at step #113, Y.sub.12 is set into the address register Y.sub. 1i at step #114, and then in case Po.sub.4 >Po.gtoreq.Po.sub.3 at step #115, Y.sub.13 is set into the address register Y.sub.1i at step #116. But when Po.gtoreq.Po.sub.4 at step #115, Y.sub.14 is set into the address register Y.sub.1i.

After setting of the address Y.sub.11, Y.sub.12, Y.sub.13 or Y.sub.14 into the address register Y.sub.1i, similar judgment is made for an exit pupil position Pz in accordance with Table 1. Thus, if Pz.gtoreq.Pz.sub.4 at step #118, then the sequence jumps to step #128, but on the contrary if Pz.sub.4 >Pz.gtoreq.Pz.sub.3 at step #118, then X.sub.14 is set into another address register X.sub.1i at step #120. Then if Pz.sub.3 >Pz.gtoreq.Pz.sub.2 at step 121, then X.sub.13 is set into the address register X.sub.1i at step #122, and if Pz.sub.2 >Pz.gtoreq.Pz.sub.1 at step #123, then X.sub.12 is set into the address register X.sub.1i at step #124. In case Pz.sub.1 >Pz at step #123, X.sub.11 is set into the address register X.sub.1i at step #125. With the settings, any location in Table 1 can be accessed with the address data of the address registers X.sub.1i and Y.sub.1i. With the address X.sub.1i and Y.sub.1i, the ROM table in which Table 1 is stored is accessed at step #126, and data stored at the location regarding distance measuring areas in which a focus condition can be detected is set to a register ERAR at step #127. The data here includes 4 bits individually representing the distance measuring areas I to IV, and a bit corresponding to a distance measuring area in which detection of a focus condition is possible presents a binary value "1" but a bit corresponding to a distance measuring area in which detection of a focus condition is possible presents the other binary value "0". Accordingly, if, for example, the address data X.sub.11 and Y.sub.11 are set up, then a data "0001" or "0011" will be placed into the register ERAR; if the address data X.sub.14 and Y.sub.13 are set up, then a data "0001" or "1001" will be placed into the register ERAR; and if the address data X.sub.11 and Y.sub.14 are set up, then a data "1111" will set to the register ERAR. Meanwhile, at step #128. "0000" is set to the register ERAR because there is no distance measuring area in which a focus condition can be detected.

Referring now to FIG. 14, the subroutine SUB2 shown is a flow wherein a distance measuring area or areas in which detection of a focus condition is possible are selected from within the out-of-axis distance measuring frames B and C depending upon an exit pupil position Pz and a deformed exit pupil outer radius Po in accordance with Table 3. Similarly as in the subroutine SUB1 of FIG. 13, when Po<Po.sub.1 at step #130 or when Pz.gtoreq.Pz.sub.4 at step #138, there is no distance measuring area in which a focus condition can be detected. Accordingly, "0000" is set to a register ERBCR. Then, if Po.ltoreq.Po<Po.sub.2 at step #131, then Y.sub.21 is set into an address register Y.sub.2i at step #132, and if Po.sub.2 .ltoreq.Po<Po.sub.3 at step #133, then Y.sub.22 is set into the address register Y.sub.2i at step #134. After then, if Po.sub.3 .ltoreq.Po<Po.sub.4 at step # 135, when Y.sub.23 is set into the address register Y.sub.2i at step #136, but if Po.sub.4.ltoreq.Po at step # 135, then Y.sub.24 is set into the address register Y.sub.2i at step #137. Further, if Pz.sub.3 .ltoreq.Pz<Pz.sub.4 at step #139, then X.sub.24 is set to another address register X.sub.2i at step #140, and then if Pz.sub.2 .ltoreq.Pz<Pz.sub.3 at step #141, then X.sub.23 is set to the address register X.sub.2i at step #142. After then, if Pz.sub.1 .ltoreq.Pz<Pz.sub.2 at step #143, then X.sub.22 is set to the address register X.sub.2i at step #144, and if Pz.sub.1 >Pz at step #143, then X.sub.21 is set to the address register S.sub.2i at step #145. Then, the ROM table is accessed with the thus set address data X.sub.2i and Y.sub.2i at step #146, and a data stored at a location thus accessed is set to the register ERBCR.

Referring now to FIG. 15, in the subroutine SUB3 shown, a distance measuring area or areas in which a focus condition can be detected are selected from within the on-axis distance measuring frame A depending upon an exit pupil position Pz and an exit pupil inner radius Po' in accordance with Table 2 above, and finally a distance measuring area in the on-axis distance measuring frame A in which a focus condition can be detected is selected depending upon both of the exit pupil outer radius Po and the exit pupil inner radius Po'. At first, in accordance with Table 2, address data X.sub.3i Y.sub.3i are determined similarly as in the subroutines SUB1 and SUB2 of FIGS. 13 and 14, respectively, at steps #151 to #165. Then, the ROM table is accessed with the address data X.sub.3i and Y.sub.3i to read out a data stored at a location specified by the address data at step #166. Then at step #167, the data thus read out and the data which has been set to the register ERAR in the subroutine SUB1 are ANDed for each bit, and the results are set to the register ERAR. Consequently, even if a distance measuring area is selected on one hand and accordingly a bit corresponding to the distance measuring area is "1", if the corresponding bit in the resulted data by selection on the other hand is "0", then the bit of the ANDed results will be "0". Thus, a distance measuring area which is determined from both of the exit pupil outer radius Po and the exit pupil inner radius Po' is set to the register ERAR. It is to be noted that since there is no distance measuring area in which a focus condition can be detected when Po'.gtoreq.Po.sub.4 ' or Pz<Pz.sub.1, "0000" is placed into the register ERAR at step #168.

Referring to FIG. 16, in the subroutine SUB4 shown, a distance measuring area or areas in which a focal plane can be detected are selected from within the out-of-axis distance measuring frames B and C depending upon an exit pupil position Pz and a deformed exit pupil inner radius Po' in accordance with Table 4, and finally a distance measuring area in the out-of-axis distance measuring frames B and C in which a focus condition can be detected is selected depending upon both of the deformed exit pupil outer radius Po and the deformed exit pupil inner radius Po'. At first, address data X.sub.4i and Y.sub.4i are set similarly as in the subroutines SUB1 to SUB3 of FIGS. 13 to 15, respectively, and then, the ROM table is accessed with the address data X.sub.4i and Y.sub.4i to read out a data stored at a location specified by the address data at step #166. Then, the data thus read out and the data which has been set to the register ERBCR in the subroutine SUB2 and ANDed for each bit, and the results are set to the register ERBCR. Consequently, a distance measuring area in which detection of a focus condition is possible is finally set to the register ERBCR. It is to be noted that since there is no distance measuring area in which a focus condition can be detected when Po'.gtoreq.Po.sub.3 ', "0000" is placed into the register ERBCR at step #187.

While in the embodiment described above the on-axis distance measuring frame A and the out-of-axis distance measuring frames B and C are provided as distance measuring frames and each of the distance measuring frames A, B and C is separated into the distance measuring areas I to IV, only the distance measuring frames A and B or A and C may otherwise be provided as distance measuring frames. Or else, only the distance measuring frame A may be provided and separated into the several areas as in the embodiment described above. Or otherwise, the three distance measuring frames A, B and C may be provided wherein the distance measuring frame A is separated into the several areas while the distance measuring frames B and C are not separated.

While the P mode (program AE mode) has been described so far as an exposure controlling mode, when a cata-dioptric lens is mounted on the camera, it is necessary to cope with the same in a different manner than with an ordinary lens also in an A mode (aperture priority AE mode), S mode (shutter speed priority AE mode) or M mode (manual mode). In particular, in the case of the A mode, an exposure time is automatically set with respect to a fixed aperture similarly as in the P mode, but in the case of the S mode or M mode, the aperture is fixed and the exposure time is manually set.

It is to be noted that while, in the foregoing description of the preferred embodiment of the present invention, data Ps, Po, Po', and .DELTA.Po and .DELTA.Po' regarding an exit pupil of a photographing lens are provided in order to judge whether or not an AF function of the TTL type can be used, such an alternative construction may be employed that the data are omitted and, in the case of a cata-dioptric lens, a signal indicating that detection of a focus condition is impossible to provide in the lens while a fully open aperture value Avo and a maximum aperature value Avmax (=Avo) are forwarded as data regarding an aperture of the lens as in the embodiment described above.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth herein.