Method and Apparatus for Transmission of Information in a Photographic Camera

The present invention provides a method to reduce the number of signal lines necessary for transmission of information on the maximum aperture and information on the minimum aperture of an objective to a camera body in a photographic camera of lens interchangeable type.

In a photographic camera provided with an automatic exposure control mechanism of shutter speed preset, i.e., priority, type, it is necessary to transmit information on the maximum aperture and information on the minimum aperture of the objective in use to the automatic exposure control mechanism. Assuming that a suitable type of film has been selected and a shutter speed has been set by the photographer, an appropriate exposure is sometimes impossible depending on the luminance of the object to be photographed, within an effective aperture range of the objective. In such a case, the photographer must be warned of this situation or photographing must be prevented, for example, by locking the shutter release. Especially when it is desired to provide a single-lens reflex camera usually used with a group of various interchangeable lenses with an automatic exposure control mechanism of shutter speed preset type, transmission of information on the maximum aperture and information on the minimum aperture is essential. With an automatic exposure control mechanism of diaphragm present, i.e., priority, type, on the other hand, it is necessary for a diaphragm value preset by the photographer to be transmitted to the automatic exposure control mechanism; transmission of the diaphragm value information is preferably done electrically in view of a fact that the essential part of the automatic exposure control mechanism comprises an electronic circuit and the camera itself is extremely small. Thus, a plurality of signal lines are required for transmission of information on the objective diaphragm to the camera body and, preferably, the number of these signal lines is as small as possible.

Accordingly, the present invention reduces the number of signal lines by deriving an electrical signal resulting from an arithmetic operation on an electrical signal representative of the maximum aperture and an electrical signal representative of the minimum aperture of the objective, and using the derived signal as the information on the maximum aperture to be transmitted from the objective to the camera body. Specifically, a photographic camera has a camera body, an interchangeable lens assembly mounted on the camera body, and an automatic exposure control mechanism located in the camera body. The mechanism responds to a first binary signal representative of a maximum lens aperture value in binary code and a second binary signal representative of a minimum lens aperture value in binary code. The first signal has a given number of binary bits. The second signal is generated in the lens assembly. A third signal representative of the arithmetic difference between the first and second signals is also generated in the lens assembly. The third signal has a number of binary bits fewer than the given number. The second and third signals generated in the lens assembly are transmitted to the camera body. In the camera body, the second signal is applied to the mechanism and the transmitted second and third signals are arithmetically added to derive the first signal, which is applied to the mechanism.

The features of a specific embodiment of the best mode contemplated of carrying out the invention are illustrated in the drawings, in which:

FIG. 1 is a logic circuit diagram illustrating an embodiment of a logic circuit for deriving a maximum aperture signal in a camera body for the case in which the minimum aperture signal is represented by a single bit;

FIG. 2 is a logic circuit diagram illustrating an embodiment of a logic circuit for deriving a maximum aperture signal in a camera body for the case in which the minimum aperture signal is represented by two bits; and

FIG. 3 is a block diagram of the components of a photographic camera relating to the invention.

In the transmission of information on the maximum aperture of an individual objective from the objective to the camera body, it is required to transmit at least ten items of diaphragm value information, i.e., 1.2, 1.4, 1.7, 2, 2.5, 2.8, 3.5, 4, 4.5, and 5.6 respectively in F-value for the commercially available group of interchangeable lens having different fully opened aperture values. Digital transmission of these information values on the maximum apertures from the objective to the camera body requires four signal lines shown by Table 1, in which C.sub.3, C.sub.2, C.sub.1 and C.sub.0 designate the binary code of a signal representative of actual maximum aperture corresponding to the respective maximum apertures in F-values. (This signal is referred to hereinafter as the actual maximum aperture signal.) As for the information related to the minimum aperture, on the other hand, the minimum aperture in F-value which is the largest one of the minimum aperture values of commonly used interchangeable lenses is used as the reference minimum aperture and the minimum aperture in F-value of the actually used objective relative to said reference minimum aperture in F-value is transmitted to the camera body. The electric signal representative of the difference of this reference minimum aperture and the minimum aperture of the actually used objective is hereby defined as the minimum aperture difference signal. Table 2 shows such minimum aperture difference signal in the case where one reference minimum aperture in F-value is 22 and the only other minimum aperture which can be selected is 32 in F-value.

It will be understood from the foregoing explanation that five signal lines are normally necessary for transmission of information on the maximum aperture and information on the minimum aperture. Now the features of the present invention will be described in reference with the cases of Tables 1 and 2.

Based on two findings that, in Table 1, three signal lines are sufficient for eight maximum apertures and the maximum aperture in F-value corresponding to the minimum aperture in F-value higher than a pre-determined value takes a relatively high value, the present invention employs as the signal to be transmitted from the objective to the camera body the maximum aperture signal expressed by ##STR1## and reproduces this maximum aperture signal as ##STR2## The minimum aperture difference signal b.sub.1 is such that b.sub.1 =0 when the minimum aperture in F-value is 22 and b.sub.1 =1 when the minimum aperture in F-value is 32. Thus, b.sub.0 is always equal to zero in arithmetic operation of formulae (1) and (2). According to the invention, the maximum aperture signal expressed by formula (1) is applied from the objective to the camera body, the arithmetic operation of formula (2) occurs in the camera body to reproduce the actual maximum aperture signal C.sub.3, C.sub.2, C.sub.1 and C.sub.0. The arithmetic operation for b.sub.1 =0 is shown by Table 3 and the arithmetic operation for b.sub.1 =1 is shown by Table 4. For example, the objective with the maximum aperture 2.8 in F-value and the minimum aperture 32 in F-value (corresponding to the case of b.sub.1 =1 as seen in Table 2) outputs the maximum aperture signal 011. In the camera body, a binary arithmetic adding operation 011 (a.sub.2 a.sub.1 a.sub.0)+010 (b.sub.2 b.sub.1 b.sub.0) occurs and therefrom the actual maximum aperture signal 101 is reproduced. As will be understood from Table 1, this objective has its maximum aperture 2.8 in F-value. Then, the objective with the maximum aperture 2.8 in F-value and the minimum aperture 22 in F-value (corresponding to the case of b.sub.1 =0 as seen in Table 2) outputs the maximum aperture signal 101. In the camera body, a binary arithmetic adding operation 101 (a.sub.2 a.sub.1 a.sub.0)+000 (b.sub.2 b.sub.1 b.sub.0) takes place and therefrom the actual maximum aperture signal 101 is reproduced. Table 1 indicates that this objective has its maximum aperture 2.8 in F-value. It will be evident from the foregoing description of the examples shown in connection with Tables 1 and 2 that three signal lines suffice for transmission of information representative of the maximum aperture according to the present invention. When the signal line for transmission of information representative of the minimum aperture is included, the necessary number of signal lines can be reduced by one according to the present invention to four; the information representative of the minimum aperture is used in the camera body to derive from the transmitted maximum aperture representative signal a usable signal for automatic exposure control.

Although the present invention has been described hereinabove with the minimum aperture being represented by a single bit, it is also possible to represent the minimum aperture by two bits-for example, 00(b.sub.1 b.sub.0) for 22 in F-value, 01(b.sub.1 b.sub.0) for 32 in F-value and 11(b.sub.1 b.sub.0) for 45 in F-value--so that the number of the minimum apertures which can be selected may be increased to four while the number of signal lines for transmission of information related to the actual maximum aperture remains three. However, such two bit representation results in the same effect as achieved by the single bit representation of the minimum aperture, in that the total number of signal lines necessary for transmission can be reduced by one.

FIG. 3 is a block diagram of the applicable components of a camera; the system has interchangeable lens assemblies with two different minimum aperture values, e.g., a F-value of 22 and an F-value of 32. Four bits of binary information, namely, a.sub.0, a.sub.1, a.sub.2, and b.sub.1 are transmitted from an interchangeable lens assembly 10 to a logic circuit 12, which is located in the camera body on which the interchangeable lens assembly mounts. By way of example, bits a.sub.0, a.sub.1, a.sub.2, and b.sub.1 could be transmitted from lens assembly 10 to logic circuit 12 by means of contact pairs at the lens mount constructed in the manner shown in the application Ser. No. 237,987 filed Feb. 25, 1981, the disclosure of which is incorporated fully herein by reference. Bits a.sub.0, a.sub.1, a.sub.2, and b.sub.1 represent the maximum aperture signal in the code set forth in Tables 3 and 4. Bits C.sub.0, C.sub.1, C.sub.2, C.sub.3 and b.sub.1 are transmitted from logic circuit 12 to an automatic exposure control mechanism 14, which in this embodiment automatically stops down the diaphragm to achieve the desired exposure. Mechanism 14 itself is convention in the art. By way of example, it could comprise the arrangement described in application Ser. No. 229,879 filed Jan. 30, 1981, the disclosure of which is incorporated fully herein by reference. As illustrated, logic circuit 12 derives five bits of information at its output from four bits of information at its input, thereby permitting a reduction in the number of bits of information that need to be transmitted from lens assembly 10 to the camera body.

FIG. 1 is a diagram of an embodiment of logic circuit 12 to execute the arithmetic operation of the formula (2) when the minimum aperture difference signal is represented by a single bit. Reference numerals 1 and 2 designate exclusive OR gates and reference numerals 3 and 4 designate AND gates. FIG. 2 is a diagram of an embodiment of a logic circuit to execute the arithmetic operation of the formula (2) when the minimum aperture difference signal is represented by two bits. Reference numerals 5 to 8 designate exclusive OR gates, reference numerals 9 to 12 designate AND gates and reference numeral 13 designates an OR gate. It should be understood that the logic circuits as illustrated by FIGS. 1 and 2 are not limiting and these logical functions may be implemented in different ways.

The arithmetic operation to be executed by the logic circuit of FIG. 1 is given by the following logical expression:

where .sym. and .multidot. designate exclusive OR and AND, respectively.

It will be understood from the foregoing description that the present invention permits the number of signal lines for transmission of information related to the maximum aperture to be reduced by utilizing information related to the minimum aperture to be transmitted from the objective to the camera body. Specifically, a modified code value for the maximum aperture signal is used in the lens assembly, namely, the coded maximum aperture signal minus the coded minimum aperture signal in the code processed by the automatic exposure control mechanism. This subtraction permits a reduction of the number of information bits representative of the maximum aperture value transmitted to the camera body without creating a negative difference value, because only a zero value of the coded minimum aperture signal is subtracted from the lower values of the coded maximum aperture signal. In the camera body, the coded minimum aperture signal is added to the modified code value to reconstruct the coded maximum aperture signal to which the automatic exposure control mechanism responds. Although the present invention has been described with respect to the transmission of digital mode, the similar transmission may be achieved in analog mode.