Attachment Member for Exchangeable Lenses

The present invention relates to an attachment member detachably attachable to an exchangeable camera lens which is adapted to be used with a camera body having through-the-lens (T.T.L.) light measuring system, and more particularly, pertains to an attachment member for transmitting information as to the maximum f-number value or minimum diaphragm aperture available for the exchangeable lens to a camera body.

In full-aperture light measurement through an exchangeable lens which is detachably mounted on a camera body, there are two types of methods of transmitting information as to the set diaphragm aperture of the lens to the camera body. The first type requires two transmitters, one for transmitting information as to the minimum f-number (full aperture value) of the lens, and the other for transmitting information as to the set f-number (diaphragm aperture value) of the lens. The second type of method necessitates only a single transmitting member which transmits information as to the step difference from the minimum f-number to the set f-number.

The present invention is directed to the latter type of information transmittal. In this type of information transmitting mechanism, it is possible to control the exposure time in accordance with scene brightness and the set f-number of the lens by taking into consideration the fully open aperture through which the scene brightness is measured, as well as to indicate, before the diaphragm is stopped down, the exposure time to be determined or executed. However, this type of mechanism is not applicable for the indication of a diaphragm aperture to be controlled automatically in accordance with scene brightness and a selected, manually set shutter speed as the single transmitting member only transmits information as to the step difference but not information as to the minimum f-number of the lens which is necessary for indication of the f-number or of diaphragm aperture value to be controlled automatically.

To make an exchangeable lens having the second type of information transmission mechanism available for camera bodies provided with a shutter-priority automatic diaphragm control, it was proposed in U.S. pat. application Ser. No. 769,832 of Kuramoto et al filed on Feb. 17, 1977, which was assigned to the same assignee as that of the present application, to provide the exchangeable lens with a second information transmitting member to transmit information as to the maximum f-number to the lens so that information as to the minimum f-number may be obtained in the camera body by combining this information with the information as to the step difference transmitted by the first transmitting member when the diaphragm aperture setting member is set to a maximum f-number or automatic aperture control position. However, this proposed mechanism requires an additional member to be incorporated into the exchangeable lens and thus conventional exchangeable lenses having only the single transmitting member cannot provide information for the indication of automatic aperture control.

Accordingly, it is a primary object of the present invention to provide an attachment member which enables an exchangeable lens having a single member for transmitting information as to the step difference from a full to a set aperture value to transmit information as to a maximum f-number of the lens to a camera body.

It is another object of the present invention to provide an attachment member for an exchangeable lens of the conventional type which is adapted only to transmit to a camera body information as to the step-difference between a minimum f-number thereof and a f-number corresponding to an aperture value set by a diaphragm setting ring of the lens, the attachment member enabling the lens to transmit information to a single lens reflex camera body such that the camera body can indicate a f-number corresponding to an automatically controlled aperture prior to a stopping-down of the diaphragm.

In accomplishing these objects, an attachment member of the present invention includes a substantially circular body adapted to be releasably attached to the outer periphery of an exchangeable lens and information transmitting means arranged on the substantially circular body at an angular position dependent on a maximum f-number of the exchangeable lens to be used therewith. When the substantially circular body is attached to the outer periphery of the exchangeable lens at the predetermined angular position, the information transmitting means of the attachment member is capable of transmitting information as to the maximum f-number of the lens to a camera body.

When the information thus transmitted to the camera body by the attachment member is combined with information as to the step-difference between the minimum f-number of the exchangeable lens and a f-number corresponding to the aperture with the diaphragm setting ring set to the minimum aperture (maximum f-number) of the lens, information as to the minimum f-number can be obtained within the camera body. With information as to the minimum f-number, indication of a f-number corresponding to an automatically controlled aperture is made possible prior to a stopping-down operation of the diaphragm. As is conventional in the art, information as to the step-difference between the minimum f-number and a f-number corresponding to the set aperture is transmitted to the camera body when the exchangeable lens is mounted on the camera body.

The manner and mechanism by which the camera body is able to receive the information transmitted by the transmitting members of the lens are known in the art and an example of such is set forth in U.S. Pat. application Ser. No. 769,832 to Kuramoto et al filed Feb. 17, 1977, the disclosure of which is hereby incorporated by reference.

Thus, the attachment member of the present invention makes it possible to use a series of exchangeable lenses of the conventional type which are adapted to only transmit to the camera information as to the step-difference between a minimum f-number of the lens and a f-number corresponding to a set aperture, with a camera body capable of indicating a f-number corresponding to an automatically controlled aperture prior to a stopping-down operation.

According to the preferred embodiments of the present invention, the substantially circular body of the attachment member has a dimension such as to be releasably attached to the outer periphery of a diaphragm setting ring or to the outer periphery of a fixed outer sleeve adjacent to the diaphragm setting ring of an exchangeable lens. In the case where the substantially circular body of the attachment member is attached to the outer periphery of the diaphragm setting ring of the exchangeable lens, the information transmitting means on the substantially circular body is capable of transmitting information as to the maximum f-number of the lens to the camera body only when the diaphragm setting ring is set to the minimum aperture corresponding to the maximum f-number. In contrast, in the case where the substantially circular body of the attachment member is attached to the fixed outer sleeve of the exchangeable lens, the information transmitting means on the substantially circular body is capable of transmitting information as to the maximum f-number to the camera body regardless of the aperture to which the diaphragm setting ring is set.

In addition, according to the preferred embodiments of the present invention, the attachment member is provided with means for indicating the predetermined position of the substantially circular body at which the substantially circular body is to be attached to a particular position on the exchangeable lens. This means facilitates the attachment of the substantially circular body to the exchangeable lens at a predetermined angular position. Furthermore, means are provided on the attachment member to restrict the movement of the circular body in an angular direction and also in the direction of the optical axis of the exchangeable lens.

The above and other objects and features of the present invention will become more fully apparent from a detailed consideration of the following description in conjunction with the accompanying drawings.

FIG. 1 is a perspective view of an exchangeable lens to which an attachment member according to the present invention may be attached;

FIG. 2 is a perspective view of an attachment member according to a first embodiment of the present invention;

FIG. 3 is a perspective view of an attachment member according to a second embodiment of the present invention; and

FIG. 4 is a perspective view of an attachment member according to a third embodiment of the present invention.

Referring now to FIG. 1, shown is a conventional exchangeable lens adapted to be mounted on a camera body (not shown) of the type having T.T.L. light measuring system. Exchangeable lens 1 includes a diaphragm setting ring 2 having a transmitting member 3 for transmitting to a camera body (not shown) information as to the step difference from minimum f-number of the lens (f:1.4 in the case of this Figure) to a f-number set by the diaphragm setting ring. In addition, exchangeable lens 1 includes a field depth indicating ring 4 having indicia 5 for setting the object distance or camera-to-subject distance. On the same field depth indicating ring 4 is a mark 6, in the shape of a small boss, for indicating the angular position of the lens relative to a camera body when the lens is to be attached to the camera body.

FIG. 2 shows an attachment member 10 in accordance with the present invention which may be detachably attached to the exchangeable lens 1. Attachment member 10 comprises a resilient, substantially circular body which may be fitted around diaphragm setting member 2 of lens 1 and which extends more than 180.degree. in circumference with a cut-away portion A having an length corresponding to the length of portion A on the diaphragm setting ring 2. At the inner side of the attachment member 10 are a plurality of regularly formed grooves 11 in the form similar to that of a caterpillar tread such that a knurl 7 on diaphragm setting ring 2 may be fitted therein. Further, a transmitting member 12 for transmitting information as to the maximum f-number of a lens to a camera body is on the attachment member 10 as a projection extending perpendicular to the plane of an edge of the attachment member. The angular position of the transmitting member 12 on the circumference of member 10 depends upon the maximum f-number of the exchangeable lens on which the attachment member 10 is to be mounted or fitted. Thus information as to the maximum f-number of the lens may be transmitted to a camera body when the exchangeable lens 1 with the attachment member 10 is mounted on the camera body and diaphragm setting ring 2 of the lens is set to the position where a letter or a sign representative of the maximum f-number is registered with indicia 5. In addition, the attachment member 10 is provided with a positioning member 13 for restricting the movement of the attachment member on the diaphragm setting ring 2 in the direction of the optical axis of the exchangeable lens 1. The outer surface of the attachment member 10 is marked with an indication of the type of exchangeable lens to which the attachment member is suitable. This indication may be a designation of the focal length and range of f-numbers available of the lens, such as f:1.4 - f:22.

Therefore, if an attachment member 10 is fitted on to an exchangeable lens 1 of the type indicated with the outer surface of the attachment member at a predetermined angular position and with the grooves 11 engaged the knurls 7 of the diaphragm setting ring 2 until the positioning member 13 engages the rear of the diaphragm setting ring, it will be possible, when the exchangeable lens is mounted on a camera body and the diaphragm setting ring is set to the maximum f-number position, to transmit information as to the maximum f-number of the lens to the camera body through the transmitting member 12. The information as to the maximum f-number of the lens thus transmitted by the attachment member to the camera body is combined with the information of the step difference from the minimum to the maximum f-number transmitted by transmitting member with ring 2 set to a maximum f-number position such that information as to the minimum f-number of the lens may be obtained by the camera body.

The mechanism of obtaining information by minimum f-number may be explained as follows with reference to APEX notation. According to the APEX notation system:

where;

Av is an aperture value to be determined by an automatic control device.

Sv is a set film sensitivity or speed value.

Bvo is a luminance value of the photographic object measured through a full aperture.

Tv is a set exposure time value.

Avo is an aperture value of a minimum f-number (full aperture) of an exchangeable lens.

Avc is an aperture value corresponding to a maximum f-number (minimum aperture) of an exchangeable lens.

Pc is a value corresponding to steps or step difference from the minimum to the maximum f-number of a lens.

As is shown in the Figures, if the diaphragm setting ring 2 of an exchangeable lens 1 to which an attachment member 10 is fitted is set to the maximum f-number position of the lens, the transmitting member 3 of the diaphragm setting ring transmits information as to the steps from a minimum to maximum f-number i.e. Pc with the transmitting member 12 of the attachment member transmitting information as to a maximum f-number, i.e., Avc. Therefore, a camera body receiving these two types of information can combine them to obtain information as to the minimum f-number (Avo) of the lens. Thus, with the information as to the minimum f-number (Avo) and the scene brightness measured through fully open aperture (Bvo), an f-number of the proper diaphragm aperture (Av) for the lens to be determined automatically may be indicated prior to actual photography.

Figure 3 shows another embodiment of the attachment member of the present invention wherein the attachment member 20 includes a substantially circular body having no opening as is provided in the first embodiment of FIG. 2. The portion of the attachment member 10 which covers the f-number scale of diaphragm setting ring 2 is made transparent so that the scale may be observed therethrough. The attachment member 20, like the attachment member 10 of FIG. 2, includes several fitting members 21 in the form of projections fittable about knurls 7 on diaphragm setting ring 2, a transmitting member 22 for transmitting information as to the maximum f-number of a lens, positioning member 23 for restricting the movement of the attachment member in the direction of optical axis of the lens, and indicating mark 24 indicative of the type of exchangeable lens to which the attachment member may be applied. The positioning member 23 of this embodiment is adapted to engage the diaphragm setting member 2 of the exchangeable lens 1. On the inner periphery of the attachment member 20 is a recess 25 through which the transmitting member 3 of lens 1 may pass when mounting of the attachment member on the lens and which also serves to determine the angular position of the attachment member relative to the diaphragm setting ring 2.

Attachment member 30 shown in FIG. 4 as still another embodiment of the present invention is constructed so as to fit onto, instead of the diaphragm setting ring 2 of a lens 1, a fixed portion of the exchangeable lens, such as the field depth indicator ring. By means of this construction, the transmitting member 31 of the attachment member 30 is always coupled with an information receptive member of a camera body when the exchangeable lens is mounted on a camera body. Accordingly, attachment member 30 should be detached from the lens so as to interrupt transmission of information as to the maximum f-number of the lens when such information is unnecessary as is the case of automatic exposure time control.

Attachment member 30 includes a generally circular body which is hinged at 30a to open and close. Hence, the attachment member 30, being opened, is mounted about the exchangeable lens and then closed and locked at 30b so as to be fixed thereto.

Information transmitting member 31 of attachment member 30 extends rearwardly, i.e. towards a camera body. The attachment member 30 also includes a notch 30c which is adapted to be engaged by small boss 6 on the lens 1 for the indication of the angular position of the exchangeable lens relative to the camera body upon mounting the lens thereon, so that location of the attachment member is fixed angularly and in the direction of the optical axis of the lens. Another notch 30d formed on attachment member 30 is registered with indicia 5 when notch 30c is engaged by small boss 6, thereby indicating that attachment member 30 is properly positioned on the lens. Attachment member 30 is also provided with indication 34 of type of exchangeable lens for which the attachment member is suitable.

With this third embodiment, it may be beneficial to form a depression or hollow 31a in transmitting member 31 to engage diaphragm setting ring 2 so as to urge the latter radially inwardly to prevent the ring from moving arbitrarily and maintain the ring in a set position.

According to the present invention as shown by the above non-limiting embodiments, by only attaching an attachment member to a lens at given location, a conventional exchangeable lens having only a single transmitting member which transmits to camera body information of steps from minimum to set f-number will allow the use of the lens with a camera in which both automatic diaphragm and automatic shutter controls are possible, as the attachment member will provide information as to the minimum f-number of the exchangeable lens thereby providing for an indication of a f-number to be determined automatically by an automatic diaphragm control mode of the camera body.

As used herein, the term "substantially circular" when describing the body of the attachment member includes a semi-circular ring like shape having a circumference of at least 180.degree. up to and including a complete closed ring like shape having a circumference of 360.degree.. The term is intended to at least encompass the particular shapes of the attachment members as shown in the present drawings.