CA1190782A - Compensation for diaphragm control in slr camera - Google Patents

Abstract

COMPENSATION FOR DIAPHRAGM CONTROL
IN SLR CAMERA

Abstract of the Disclosure A camera comprises a camera body and first and second lens assemblies interchangeably insertable into the camera body. Each lens assembly has a displaceable actuator, a diaphragm adjustable between a maximum aperture and a minimum aperture value responsive to displacement of the actuator and a transducer for generating a first signal representative of the displacement of the actuator. In the camera body, there is generated a second signal repre-sentative of the desired aperture value of the diaphragm for correct exposure. The first and second signals are compared and the actuator of the lens assembly inserted in the camera body is displaced responsive to the comparison to stop down the diaphragm from the maximum aperture value toward the minimum aperture value until the first and second signals assume a predetermined relationship. The diaphragm of the second lens assembly is maintained at the maximum aperture value during an initial portion of the displacement of the actuator. Preferably, the initial portion of the actuator displacement is sufficient to compensate for the deviation in aperture value, maximum aperture value, and minimum aperture between the first and second lens assemblies.

Description

`` ~190~ 2 This invention relates to compensation in a single-lens reflex (SLR) camera and is par-ticularly applicable to such a camera having automatic exposure capability and in-ter-changeable lenses.

It is well known for the single-lens reflex camera using an interchangeable lens that, when a photometric opera-tion is done within the camera through an in-terchangeably mounted lens with the diphragm of said lens being fully opened (so-called TTL photometry wi-th fully ~L~9~)7~
--2~
1 opened opened diaphragm), using a resultant value by directly coupling it with an exposure meter or subjecting said value to an automa~ic exposure control operation would lead to a great error between an exposure value to be set and said photometric value so that a photographing result with a proper exposure would not be obtained.
Such deviation or error i5 largely classified into one due to optical characteristics of individual lenses inter-chanyeably mounted on a camera and one due to the specific position of the light receiving element with`lncamera. The former is caused by the fact ~hat the lens aper~ure stopped down by a diaphragm adapted to be preset by a diaphragm preset ring at the moment o-f photographing cannot produce an accurate multiple proportional variation of actual illumination intensity in the film plane corresponding to a multiple proportional variation of preset diaphragm value marked around the diaphragm preset ring. More specifically, individual interchangeable ~ are different in their lens materials, lens arrangements and assembling modes, so that the illumina~ion intensity in the film plane depends upon the light transmissivity characteristics, a vignetting effect peculiar to each lens, and particularly s~-called aperture eclipse occurring with the fully opened diaphragm which substantially reduces the effective illumination intensity in the film plane when the lens aperture is held close to its fully opened diaphragm value.
In consequence, the illumination intensity in the film plane is reduced in its effective value and varies in a mode far from said multiple proportional variation as the lens aperture approaches to the fully opened diaphragm value.

1 At the same time, the illumination intensity, which is practically uniform and multiple proportionally varies substantially in correspondence with the successive steps of preset values marked around the periphery of the diaphragm preset ring, can be obtained wi~hin a ranye of relatively small lens aperture values, for example, less than an F-value of S.6. The effective ~alue of the illumination intensity in the film plane is substantially reduced at the fully opened diaphragm (the maximum lens aperture) and the resultant value of photometric operation carried out at this fully opened diaphragm cannot be utilized to obtain a proper exposure, since it would be impossible, from ~ resultant value, to produce a multiple proportional variation of ex-posure exactly or acceptably corresponding to the multiple proportional variation of successive preset values within the range of relatively small lens apertures and thereby to obtain an exposure time corresponding to a preset diaphragm value. Such error appearing in the film plane due to variation of illumination intensity depending upon individual interchangeable objectives i5 referred to herein as the illumination intensity error in the film plane.
The photometric element exposed to the light coming through the lens with fully opened diaphragm would ~e preferably located just in the film plane so that said photometric element may be operatively coupled to an ex-posure meter or utilized for automatic exposure control to obtain a proper exposure. ~owever, if the photometric operation were actually performed just in the film plane, ~photometric element would be a critical n~ R~ r for film exposure in photographing and thus the photometric 1 element is located not in the film plane itself~but at a position which is equivalent to said film plane or causes little photometric deviation from the value which would be obtained from the photometric operation performed just in the film plane. Such photometric position equivalent to the film plane could be, for example, a position of a focusing plate on which the light reflected by a mirror is focused and this posi~ion is, in fact, preferred in that it is in a conjugate relationship with the film plane.
However, this position would be an obstacle not only for the user's view through a viewfinder,but also for the user's focus adjusting operation. Accordingly, the photometric _ element has usually been located, in most cases, on the ~ight exit end surface of a pentagonal~dachkant prism or similar optical system for reflection and inversion of light. Such prism has been mounted on the focusiny plate, particularly along the periphery of a viewfinder eyepiece so that a viewing therethrough should not be prevented.
Even such position of the photometric element has resulted in the ~orbl~m that a photometric result is obtained as a value slightly lower or dar~er than the illumination intensity actually given in the film plane. The reason is that the position o~ the photometric element is deeper than the position of the focusing plate, which is practically equivalent and conjugate to the film plane, by the length of the optical reflection and inversion path defined by said prism, and there occurs less light absorption by said prism.
It will be obvious that such location of the photometric element has never achieved the intended photometric effect exactly equivalent to that obtained from the photometric 7~32 opera-tion performed -just in -the film plane and has necessarily resulted in an error depending upon the focal distance of each interchangeably mounted lens. An error of this type is referred to herein as the illumination intensity error due to the position of the photometric element.

Thus, the respective errors as above-mentioned inevitably appear as various quantities of deviation from the actual photometric values which should be obtained through the fully opened diaphgrams no matter whether the objectives have the same value of their fully opened d.iaphragm or the same Eocal distance. Details of these errors are illustra~
ted and described in applicant's U.S. Pa-tent No. 3,486,434 issued December 30, 1969.

With the photographic camera of so-called diaphragm regulation priority type, it is usual to transmit an informa-tion signal corresponding to a preset diaphragm value from the lens to a photometric instrument or its associated cir-cui-t or an exposure control circuit in the camera body by suitable mechanical means such as a cam (an example o~ such means is disclosed in Japanese Patent Publication No. 53 (1978)-33064, published 1978) or by suitabl~ electrical com-pensator means such as a variable resistor control of special arrangement depending upon a diaphgram value actually pre-se-t so -that exposure control of high precision can be achieved with an effective compensation of the errors as men-tioned above, and thereby a proper exposure is given.

According to one aspect of the invention, compen-sation is mechanically introduced into an automatic exposure control operation by providing a preliminary displacement, which has no effec-t on the aperture value. A camera compri-ses a displaceable actuator and a diaphragm adjustable bet-ween a maximum aperture value and a minimum aperture value _ 5 ~07~3;2 responsive-to displacement of the ac-tuator. A first signal representa--tive of the displacemen-t of-the actua-tor and a second signal representa--tive of the desired aperture value of-the diaphragm for correct exposure are generated. The first and second signals are compared. The actuator is displaced upon shutter release. The displacement of the actua-tor is arrested responsive to the comparison to stop down the dia-phragm from the maximum when the first and second signals assume a prede-termined rela-tionship. The diaphragm is maintained at the maximum aper-ture value during an initial portion of the displacement of -the actuator, i.e., a pre-liminary displacement which permits compensa-tion for dif-ferent types of errors depending upon the amount of the initial portion of -the actuator displacement.

15 , According to another aspec-t of the invention, a camera comprises a camera body and first and second lens assemblies interchangeably insertable into the camera body.
Each lens assembly has a displaceable actua-tor, a diaphragm adjustable between a maximum aperture value and a minimum aperture value responsive to displacement of the actuator and a transducer for generating a first signal representa-tive of the displacemen-t of the actuator. In the camera body, there Q~

1 is generated a second signal representati~e of the desired aperture value of the diaphragm for correct exposure~ The first and second signals are compared and the actuator of the~lens assembly inserted in the camera body as displaced responsive to the comparison to stop down the diaphragm from the maximum apertuxe value toward the minimum aperture value until the first and second signals assume a predeter-mined relationship. The diaphragm of the second lens as-sembly is maintained at the maximum aperture value during an initial portion of the displacement of the actuator.
Preferably, the initial portion of the actuator displace~
_ ment is sufficient to compensate ~or the deviation in aperture value, maximum aperture value, and minimum aperture, between the first and second lens assemblies.
Thus, for any giuen ac~ual aperture value, the first signal varies from lens to lens depeliding upon the characteristics of the particular lens mounted on the camera hody.

` 25 ~5 ~9o~

1 Brief Description of the Drawings 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 schematic diagrarn illustrating the relation-ship between different parameters of a plurality of interchangeable lenses as represented by resistance values .selected by a lever operatively associated with a diaphragm preset ring;
FIG. 2 is a block schematic d.iagram of an automatic diaphragm control system ~ncorporatin~ the principles of the invention;
FIG. 3 is a rear view of a diaphragm mechanism illustrating the use of a preliminary displacement that does not affect the aperture value of the diaphragm;
FIG. 4 is a graph illust~ating the relationship between delay time and stopping distance of a plurality of interchangeable lenses;
FIG. 5 is a front view o~ a camera body and a rear view of an interchàngeable lens illustrating the mounts on such camera body and lens with electrical contacts; and FIG. 6 is a schematic diagram of a diaphragm actuator . and displacement transducer therefor.

07~
g 1 Detailed Description of the Specific Embodiments According to the present invention, various error quantities of the previous mentioned two categories depend-ing upon different objec~ives int.erchangeably mounted on a camera body are compensated by a displacement quantity sccurring in the mechanically operative system when the :~
operation of stopping down is mechanically transmitted from the camera body to the lens so that the precision of automatic exposure control is effectively improved in an exposure priority mode.
The conception of the invention to achieve such objeot will now:be considered by way of a simplified example.
-- Assuming that, with respect to a lens A having a fully opened diaphragm value of F 1.4 as the reference lens, the light quantity coming through another lens X having a fully opened diaphragm value of F 1.4 and being inciden~ upon the light receiving element corresponds only to the light 378%

1 quantity which will come through said lens A when the latter is stopped down to a value of ~ 1.7; the light quantity ob-tained through the lens X is considered to be lower ~y 0.5 EV
than through the reference lens A~ If a relationship of Av' = Bv' + Sv - Tv is established with respect to the reference lens A, application of Apex operation Av = Bv + Sv - Tv will give a relationship Av" - (Bv' - O.S) Sv - Tv with respect to the lens X.
For example, conditions are assumed as follows:
~r~
Brightness of~object to be .~ photographed:Bv = 8~EV~, ~-- Film sensitivity:Sv = 5(EV), Exposure time:Tv = 8(EV), and Bv' = 7.

(It is assumed here that, also concerning the reference lens A, the effective illumina~ion intensity incident on the light receiving element takes a value lower by approxi-mately 1 EV and, even with the fully opened diaphragmvalue of F 1.4, not Bv' = 8 but Bvl = 7.) Calculation according to the above mentioned formulae based on these exemplary values sives respective values of Av, Av', and Av" as follows:

Av = 5, Av' = 4(EV), Av" - 3.5(EV), wherein Av = 5 indicates that the diaphragm value after the operation of stopping down corresponds to F 5.6.

4 ~9~

1 With respect to the reference lens A, if the displace-ment quanti.ty o~ the mechanically operative system during the operation of stopping down is provided with a portion for error compensation corresponding to 1 EV as a prel; m; n~ry displacement quantity of the diaphragm driving member or the transmission member associated therewith that takes no part in the light intensity quantity control effect, the displace-ment quantity of said diaphragm driving member that actually takes part in the operation of stopping down will substantially correspond to Av' + 1 = 5(EV) and thereby a diaphragm value Av - 5 (.corresponding to a diaphragm value of F 5.6) will be obtained. The lens X similarly provided with a preli mi n~ ry displacement correspondin~ to 1 EV will be stopped down by Av" + 1 = 4.5(EV) to Av - 4.5 (corresponding to a diaphragm value of 4~5 a~ter stopped down) with a deviation of 0.5 EV
from the reference lens A wi~h ~espect to the same object to be photographed. To overcome such deviation, the --- prel; m; n~ ry displacement quantity of the lens X is set 0.5 EV
smaller than that of the lens.A (set to a quantity correspond-in~ to 0.5 EV) so that the lens X is stopped down by aquantity of Av" + 1 = 4.5 EV to the position Av = 5 (cor-responding to the diaphragm value of F 5.6~ in coincidence with the case of the reference lens A.
The basic conception o~ the present invention thus lies --~ 25 in ~chieving the desired error compensation by providing a part of the mechanically operative system adapted to transmit .
movement of the diaphragm dxiving member operating in the camera body to the diaphra~n blades in the lens with a di.s- . _ placement quantity that takes no part in the liyht quantity ~o control through the operation o~ stopping down in operative 1 association with said transmission so that various errors such as ~he difference of the fully opened diaphragm values (maximum lens apertures), the ill~mination intensity errors in the film plane depending upon individual objectives, and the illumination intensity er~rs due to the positions of t:he respective light receiving elements are properly and reliably compensated with a highly precise diaphragm value as a result o~ stopping down.

. ..

o~

Before describing the construction of the present invention in detail, procedures for compensa-tion of said errors wi11 be considered with respec-t to the pho-tographic camera of diaphragm adjustmen-t priori-ty -type and -the compen-sa-tor means according -to -the present invention will be des-cribed along with these procedures for be-tter comprehension.
Referring to Fig. 1, R designates a variable resis-tor pro-vided in the camera body, of which a resistance value is selectively set by a lever opera-tively associated with a diaphragm preset ring of the respective objective inter-changeably moun-ted on the camera. Specifically, a resistance value of said variable resistor R peculiar -to a given preset diaphragm value is set as said diaphragm preset rin~ is rotated to said given preset diaphragm value. In this con-lS nection, reference is made to Suzuki et al ~.S. Patent No.3,486,434, which issued December 30, 1969. Point or terminal Q of the variable resistor R is adjus-ted by a diaphragm index member on each particular lens in the manner depicted in the Suzuki et al patent as suc~ lens is installed in the camera body. The position of the index member on each lens established the ~Av value therefor. Even when one objective has -the same fully opened diaphragm value as another objective, the respective effec-tive values of illumination in-tensity in the film plane are different from each o-ther a-t their fully opened diaphragm values insofar as they are different in their lens designs or other aspect. When they are the same in their fully opened diaphragm values but different in their focal dis-tances, there occurs, in 1 addition to a variation of the illumination intensity error in the film plane, a variation of the illumination intensity error due to the position of ~he photometric element. As a result, the resistance value of the variable resistor R
selected by the lever of each objectiYe at the fully opened diaphragm value should be peculiar to this objective.
In ~iew ofthe fac~that the objectives interchangeably mounted on the camera may be the same both in their fully opened diaphragm values and in their focal distance but different in their lens designs, or the same in their focal distances but different in their fully opened diaphragm values, or the same in ~ ulIy opened diaphragm values but different in their focal ~istances, and so on, one objective which is considered most standard is chosen as the reference lens on the basis oE which all the other different objectives are subjected to desired compensation so that the levers operative-ly associated with the diaphragm preset rings of the respective interchangeable objectives may select proper resistance values at their fully opened diaphragm values. It is obvious that, also with such reference lens (hereinafter referred to as the reference lens A and illustrated as suc~ in FIG. 1), the effective illumination intensity in the film plane is lower than the level according to the associated nominal diaphragm -~ 25 value so far as the fully opened diaphragm value or a range of values adjacent thereto is concerned while a series of multiple proportional diapnragm values within a range of relatively small diaphragm values bring about substantially multiple proportional variation of illumination intensity in the film plane. Obviously~ a photometric result is in-fluenced not only by such general characteristics but also by the illumination intensity error due to the position of the photometric element.

~15-1 Based on the illumination intensity error in the film plane and the illumination intensity error due to the posi-tion o~ the photometric ~1 ~m~nt determined with respect to the reference lens A (for example, having a fully opened diaphragm value of F 1.4), the ~ operatively associated with the diaphragm of this reference lens A is adapted to be driven and positioned so that respective preset diaphragm values corresponding to regular interval graduations on the diaphragm preset ring, which are representative of multiple proportional diaphragm values, may result in proper selec-tion of respective resistance values utili~ea for arith-metic operation or the photometri-c circuit of the automatic exposure control circuit. Then, a relative positional rel~tionship between the varia~le resistor R in the camera bo~y, of which the resistance value is selected by the lever operatively associated with the diaphragm value preset ring of the reference lens A as a given diaphragm value is preset, and the diaphragm preset ring a adapted to drive said lever would be as illustrated by (A) of FIG. 1. Under this positional relationshi:p, a lens B being the same in its fully opened diaphragm value F 1.4 but different in the other aspects has its diaphraym preset ring b positioned as illustrated by (B) of FIG. 1 and further, another lens C
having a smaller lens opening with its diaphragm preset - 25 ring c positioned as illustrated by (C) of FIG. 1. It should be noted here that the positional relationship has been illustrated in FI~. 1 as the relative positions of the respective diaphragm values of the preset rings when the diaphragm values of the respective lenses are preset to their ~ ~9~37~

. -16-1 fully opened diaphragm values to facilitate understanding of the various features o~ the present invention which are described below.
By a~justably rotating the aiaphragm preset ring of the respective lenses A, B, and C from such relative position~l relationship, both the illumination intensity error in the film plane and the illumination intensity error due to the position of the photometric element are so effectively com-pensated that not only is a pho-tometric signal correspond-ing to the actual illumination intensity in the film planeproduced through the fully opened diaphragm transmitted to an arithmetic section of the photometric circuit or the exposure control circuit but also a given diaphragm value preset by rotating the diaphragm preset ring from the fully open position properly brings about a correspondingly multiple-proportional value of exposure.
Such method of error compensation falls under a clas- -sification in which the information on diaphragm value applied to the arithmetic sec~ion of the exposure control circuit according to the a-iaphragm value priority mode is replaced by a resistance value selected by a given preset diaphragm value. When this method of error compensation is applied to the shutter speed priority mode in which an exposure time is set with priority and then the objective - 25 is stopped down to a diaphragm value corresponding to a ~ resistance value which will give a proper exposure, the result will be as follows. The resistance value given as a result of such stopping down already includes an effective compensation of both the illumination intensity error in the film plane and the illumination intensity error due to the ~ 3.907~

position of the photometric element and, accordingly,.this resistance value may be u-tili~ed as an arithme-tic factor for automatic exposure regulation to introduce a quan-tity of actuation for automa-tic diaphragm con-trol. On the assump-tion that the same diaphragm preset ring as used for thediaphragm priori-ty mode is utilized, a preset position for automatic diaphragm control is selected on said diaphragm preset ring a-t a predetermined angular or rotational distance (corresponding to a as illustrated and in this case, av>- 0) from the rotational position :Eor -the fully closed diaphragm value so tha-t both the illumination intensity error in the film plane and the illumination intensi-ty error due to the position of the pho-tome-tric element may be effectively com-pensated for in operation of stopping down. Such preset posi-tion for autmomatic diaphragm con-trol depends upon in-dividual interchangeable objectives as illustrated by Fig. 1, in which the diaphragm preset ring a of the reference lens A has its automatic diaphragm control marking (Auto) at an angular distance a from the marking of the fully closed diaphragm value F 22. The diaphargm preset ring b of the lens B, which has the same fully opened diaphragm value and fully closed diaphragm value as the reference lens A, has a lever opera-tively associated with the diaphragm of lens B, whlch by its position compensates for -the illumination inten-sity error in the film plane and the illumination intensityerror due to the position of the photometric element. The ring b bears its peculiar preset posi-tion for automatic dia-phragm control (Auto) at an angular distance a AvB from the corresponding position for the references lens A. Similarly, the diaphragm preset ring ~ 17 -~.~9()7B2 1 of the lens C has its peculiar preset position (Auto) for automatic diaphragm control at an angular distance ~AvC from the corresponding preset position for the reference lens A
when the fully closed ~iL~ J"' value is at F 32 and at an angular distance Q~v'C when the fully closed diaphragm value is at F 22. As will be readily understood, these angular distances or deviations or ~Av in general, are determined depending not only upon the aeviations (-~RvB for the lens B
and ~RvC for the lens C) due to dif~erent poi~ts of starting the operation which are, in tur~, determined by different fully opened diaphragms ana other characteristics peculiar to the respective objectives interchanseably mounted on ~-' the camera but also upon the different fully closed diaphragm values marked on-the respective diaphragm preset rings 1 According to the present invention, therefore, the deviation due to different fully closed diaphragm values depending upon the respective interchangeable lenses is transmitted from the lens interchangeably mounted on the camera to the camera body as an information signal for the automatic exposure control in the exposure time priority mode (so-called shutter prlority mode). Further, the devia-tions such as ~RvB and ~RvC ~Rv in general), which can be known in advance, inclusive of ~he different fully opened diaphragm values depending upon the respective lenses interchangeably mounted on the camera, the illumination intensity errors in the film plane, and the illumination intensity errors due to the position of the light receiving element, are replaced by a compensation value as a portion of the displacement quantity occurring in the mechanically operative system of the respecti-ve interchangeable lens functioning from the camera body towards the diaphra~m blades, so that automatic exposure control can be realized at a high precision.

-.~ 2~

1 From the basic conception as mentioned above, an arithmetic expression est~blished when the diaphragm preset ring has been set to the automatic diaphragm control position (Auto) wiIl be considered. This expres-5 sion is given in the following form according to the ex-posure time regulation priority ~ode ~or the shutter priority mode), assuming that all the units are represented by EV values.

10 Av = Bv'.+ Sv - Tv t- ~Av - aAmin + 1 (1) wherein:
_ Av : diaphragm value;
lS Bv' : brightness value of object to ~e photographed a~ter transmission through the objecti~ei Sv : sensitivity value of film used for photographi ng;
Tv : shutter speed value set with priority;
QAv : deviation ~r~m reference lens A;
~nin : difference betwePn the fully closed diaphragm value of the reference lens A
and the fully closed diaphragm value of each lens interchangeably mounted on the camera,- with respect to the fully closed diaphragm value F 22 of the reference lens A, as illustrated by FIG. 1, ~Amin = O when the lens to be mounted on the camera has a fully closed diaphragm value of F 22 while Q7~

~min - -1 when the lens to be mounted on the camera has ~ ~uliy closed diaphragm value of ~ 32, and such information i~
transmitted from the lens to the arithmetic circuit in the camera body as the deviation or difference sign~l simultaneously when the lens is in~erchangedO (1 is the EV value given relative to the fully opened diaphra~m value F 1 4 of ~he reference lens ~.) Compensation for the illumination intensity error in the , film plane and the illumination intensity error due to ? the position of the photome~ric or light receiving element has already been incorporated into the diaphragm value Av obtained by the previously ~entioned expression (1). In the case in which the diaphra~n value i5 preset by rotation of the diaphragm preset ring in the di aphLagm value priority mode, instead of relying upon the automatic diaphragm control (Auto)~ .the shutter speed can be ob-~ tained by mutually transferxi~g the terms Av and Tv insaid expression (1), namely Tv = Bv' + Sv - Av + ~v - ~Amin + 1 . (2) 25 The exposure control and its value may be used ~or display within the viewfinder.
Operation of the automatic diaphragm control is ac-complished when a m~mhPr provided in the camera body -operatively associated with the shutter release drives a ~9(~

1 release plate in the lens and thereupon the release plate is displaced from a position at which the diaphragm mechanism is held fully opened to a position at which said diaphragm mechanism reaches a given EV value. A displace-ment quantity of said release plate is in lînear proportionto a quantity of stopping dawn and, therefore, the Av value obtained from said expression ~1) cannot be directly utilized as a control value for the diaphragm. When a value, for example, Av =-5 (F 5.6) is used as the arithmetic operation value for the aiaphragm control, stopping down hy a quantity of 4 EV results n stopping down to F 5.6 or an objective having its fully opened diaphragm value of F 1.4 (Av = 1). In this case, when the fully opened dia-phragm value of the lens is F 4 (Av = 4), F 5.6 (Av - 5) can be obtained by stopping down of the leIls to an amount cor-responding to 1 EV. Thus~ the EV quantity necessary for a desired quantity of stopping down is obtained in the form of a difference or deviation between the EV value as a result of arithmetic operation ana the fully opened diaphragm ex-pressed in EV value, and the Pv expressed in EV value asthe control quantity is given by the following foxmula:
l~Amir.
Pv = Bv' ~ Sv - Tv ~ AAV - 4m~ + 1 - Amaæ
= Av - Amax (3) wherein Amax represents the EV value at the fully opened diaphragm depending upon individual lenses interchanged~
It will be obvious from the above formula that the Pv expressed in EV value as the control quantity depends upon the fully opened aiaphragm values of the respective 7'~

1 lenses, which determine a precision of said control quantity Pv. Accordingly, when a particula-~ lens is mounted on the camera it is reguired ~o transmit the fully opened dîa-phragm value peculiar to the lens from the lens to the camera body as a signal which identifies this lens.
Generally, the objectiYe preferably has a large value of its fully opened diaphragm to be used for photographing, since it provides a viewf; n~r image sufficiently bright to detect an exactly focused point during focus adjustment as well as for viewing the composition of a scene. It also enlarges the range of stopping down, and thereby enlarges the exposure range that c~ ~e photographed. However, this preferable condition is adversely limited by the requirement for various aspects such as optical characteristics and lens size. Thus, it will be practically difficult and even disadvantageous to extract Amax signals in said formula (3) for all the interchangeable lenses~to transmit them to the camera body, in view of factors such as required space, cost, and reliability.

1 To overcome such problem, the present invention proposes that an error in the automatic diaphragm control due to the differences of the fully opened diaphragm values, the illumination intensity e~ror in the film plane~ which is characteristic o~ eacb le~s, and the illumination in-tensity error due to the positio~ of photometric element, be compensated by a special opera~ion of the member taking part in the diaphragm control, ~amely, the diaphragm driving member in the camera bo~y or a member operatively associated therewith to bring the diaphra~n mechanism to a position corresponding to the desired diaphra~m value.
The term "a special operation" used herein means the part in the course of the o~e~a~ion of an operative system starting from said diaphragm driving member in the camera body and terminating in the diaphragm blades that directly takes no part in stopping said diaphragm blades down to the desired diaphragm value. This operation taking no par-t directly in stopping down wiLl be referred to herein as a "preliminary displacement" ~nd a quantity of displacement of the members constituting said operative system during said operation taking no part in stopping down, namely, before the operation for stopping down the diaphragm ~lades actually starts to stop the lens aperture down beyond the fully opened diaphragm to the desired value for control cf the light quantity, will be referred to herein as a "quantity of prel;~;n~ry displacement.
Substitution of ~Av - ~Amin + 1 - Amax = ~Rv (4) 1 into said formula ~3) and replacement of the value correspond-ing to ~Rv depending upon the individual lenses by said quantity of preliminary displacement make disappear the Amax signal corresponding to the EV value depending upon the fully opened diaphragm value fxom said formula ~3) and the EV value of Pv as a control quantity is given by Pv - Bv' + Sv - Tv ~ ~Rv (5 Such aspect will be consi~ered with respect to the lenses C and B of FIG. 1. The preliminary displacement quantity .-- of the lens C may be set larger by ~RvC with respect to the ~ lens A and t.he preliminary displacement quantity of the lens B may be set smaller by ~.RvB with respect to the lens A to eliminate the deviation due to different values of the respective fully opene2 diaphragms, the light intensity error in the film plane depending upon the individual objectives, and the light lntensity error due to the posi-tion of the photometric element-.

o~
~6-1 An example of a single-lens reflex camera in which the automatic diaphragm control is effected according to such arithmetic formula is illustra~ed by FIG. 2, wherein CA
designates a camera and B~ desiynates the brightness of an object to he photographed. It has previously been mentioned that a light quantity coming ~rom the object having its brightness Bv through the objective and to which a photo-metric element PE is-exposed ~akes an inherent value de-pending upon a fully opened aperture of this lens, a light absoxption coefficient, an internal re1ection and vignetting effect of this lens, and other factors. An output provided from the photometric element PE is log-comp.ressed by a Bv' ~~ generator Cl in the form of Bv' = Bv - (~Av - ~Amin + 1~ (6~

and then applied to an arithmetic circuit C2, which is also applied with an information.signal Tv based on the exposure time (shutter speed) set with priority and another informa-tion signal Sv based on the sensitivity of the film in usefrom a shutter speed regulating memb`er C3 and a film sensitivity regulating member C4, respectively. Thus, the arithmetic circuit C2 provides a resultant information signal as follows:
Bv' + Sv - Tv (7) When an interchangeable lens is mounted on the camera CA and its diaphragm preset ring is rotated to the automatic ~ ~07~3~

diaphragm control position (Auto), a value Av peculiar to this lens and a constan-t value 1 added thereto through circuit processing is ~ Av + 1 (8) which is the output from a compensation signal member C5 and input to an arithme-tic circui-t C7. The ari-thmetic circuit C7 is also supplied wi-th an information signal ~ Amin (g) whic}l corresponds to a deviation of a fully closed diaphragm value peculi.ar to this lens from the fully closed diaphragm , value of the reference lens A from a minimum aper-ture signal member C6. As a result, the ari-thmetic circuit C7 provides a resultant output ~ Av ~ ~Amin + 1 (10) This ou-tput is applied together with the ou-tput expressed by the formula (7) coming from said arithmetic circuit C2 -to an arithmetic circuit C8 in which an arithmetic operation (7) -~ (10) is performed.

Bv' -~ Sv - Tv + ~ Av - ~ Amin + 1 = Av Substitution of Bv' from the formula (6) gives Bv -~ Sv - Tv = Av (11) and thus it is possible to obtain an Apex quantity Av of the diaphragm value.

(37~

1 Such Av value can be displayed within a viewfinder by a display circuit Cg consisting, for example, of a meter.
The information signal Av subjected to this display merely indicates a diaphragm value providing a proper ~xposure with respect to the exposure time (shutter speed) set with priority but not the automatic control quantity as it has previously been mentioned.

~29-1 To effect stopping down with the automatic diaphragm control quantity Pv in operative association with the operation of the shutter release, said output ~7) provided from the arithmetic circuit C2 and ~h~ diaphragm value signal Av' formed by a diaphragm valu~ signal generator memher C10 according to the diaphragm value of the lens are applied to a comparator circuit Cll so that both these signals are compared to each other in said comparator circuit and, when the output Av' reaches said output Av~ the coincidence signal output is applied to a diaphragm control circuit C12 and thereby a diaphragm control magnet EEmg is released, with an effective result that the diaphragm value is adjusted -- to said Av corresponding to the arithmetic result.
A voltage source is connected across variable resistor R and the signal ~Av is the voltaye between points Q and P
of resistor R, which is the input to compensation signal member C .

Minimum aperture signal member C6 could comprise a voltage source and a resistor in the camera body connectPd through contacts discus5ed below in connection with FIG. 5 in series with a ~Amin representative resistor in the particular lens. The minimum aperture signal is the voltage appearing across the ~Amin representative resistor of the particular lens.
After the shutter release of the camera is actuated, the value of Bv' produced by generator Cl remains fixed for the rest of the automatic exposure control operation.
Thus, generator Cl produces a static signal. Diaphragm value signal is input by a photo-coupler which consists of an LED and a PE' (another photometric element, not the ~l~Q~

1 same as PE) as shown in FIG. 6. The number of pulses from PE' is in proportion ~o A~'. Du:ring the automatic exposur2 control operation, while ~he inputs to comparator 13 differ, the diaphragm stops aown ~rom its m~; mllm value responsive to diaphragm control control ma~let EEmg. When the inputs to comparator C13 are egual, a stop signal is generated to fix the diaphragm value.
FIG. 3 i~lus~rates by way o~ example an arrangement in which said preliminary ~splacement occurs in a part of the members constituting the operative system interposed between the diaphragm driving member in the camera body and - the diaphragm blades in the le~s before said diaphragm blades begin to be moved from the ~ully opened position to the desired stopped down position or control of the light 1~ quantity.
Referring to FIG. 3, S designates one of diaphragm blades, which together form an iris diaphragm, and 11 designates a diaphragm blaae actuating ring, which rotates the diaphragm blades S around an associated pivot pin 21.
Said diaphragm blade actuating ring 11 itsel is adapted to be rotated around the g~lcoGnl~ axis with respect to a stationary part of the lens barrel. The numeral 12 desig-nates a plurality of cam grooves formed in said diaphragm blade actuating ring 11 and a stationary pin 22 on each blade S is adapted to ride in each groove. On the side of said diaphragm blade actuating ring 11 there is mounted a pin 13 adapted to engage a release plate 31 which is, in turn, driven by the diaphragm driving member actuated in the camera body in operative association with the operation o~
the shutter release. The diaphragm blade actuating ring 11 3~

07~3~

1 is biased by a spring in the direction opposed to the direction indica~ed by an arrow in EIG. 3 so that said diaphragm blade ac~uatin~ ~ing 11 normally tends to open the iris diaphragm toward its fully opened position. The position of the release plat~ 31 as illustrated corresponds to the starting position o~ ~his release plate 31, at which each diaphragm blade S takes its positions I indicated by broken lines. The inner edge of each diaphragm blade S is situated behind ring 11 so as not ~o protrude into a circular opening 23 in ring 11, which de~ines the maximum aperture of this lens. From this position, each diaphragm blade S is rotated around the respective pivot pin 21 with its associated pin 22 being guided along the associated cam groove 12 as the release plate 31 is urged upwardly by the diaphragm driving member or a transmission member thereof in the direction indicated by the arrow and ~h~reby the diaphragm blade actuating ring 11 is rotated via the pin 13, until each diaphragm blade S reaches its position II indicated by phantom lines, at which its inner edge is brought into coin-cidence with the.periphery of said circular opening 23~The position II of each blade S corresponds to the positions of blades of the fully openea diaphragm. Further rotation of the diaphragm blade actuating ring 11 actually begins to stop the lens down beyond the position II of each diaphragm blade S. Thus, during movement from the position I to the position II, the respective diaphragm blades S have no unction of incident light quantity control and movement of the release plate 31 does not actually cause the diaphragm to stop down. The operation of said release plate 31 rom the starting position to the position illustrated by phantom 3~

1 lines corresponds to the preliminary displacement which is an important feature of the present invention and the quantity of the preliminary ~isplacement is given as Lv.
Thus, in this embodiment, T~ ng 11 serves -two functions --to actuate rotation of blades S and to mask blades S duringthe preliminary displacemen~ so there is no change in diaphragm value, i.e., no light quantity control. Although the quantity of preliminary displacement, Lv, occurs as a relative movement of the release plate 31 and the diaphragm l~ blades S in the embodiment as illus-trated in FIG. 3, this may be set as a relative movement between the diaphragm driving member in the camera boay-and said release plate 31, ~ such as for example by means of a lost motion linkage between a displaceable actuator and release plate 31; the lS displacement transducert generator ClO, is connected to the actuator and the amount of lost ~otion varies from lens to lens to provide the desired Lv.
To provide the individual lenses, for example, the lenses B and C, with respective prel;m;~ry displacement quantities Lv, these quantities may be selected so that Lv = a - ~RvB for the lens B while Lv = a + aRvC for the lens C, as it has previously been mentioned, when the reference lens ~ has its quantity of preliminary displace-ment expressed by ! 25 Lv = Q.

~07~
, -33-1 However, these quantities o~ preliminary displacement thus selected are based on the assumption that the operative system provided on the respective interchangeable lens to effect the operation of stopping down i~ free from a mechani-cal load during the actual operation of stopping down and there occuxs no time delay due tc this mechanical operative system. In fact, it has bee~ found that the mechanical operative system for stopping down is accompanied by a mechanical time delay particularly in the time period from application of a signal to tprminate stopping down to the actual termination thereof, and such mechanical time delay must be considered in arrangement of said mechanical opera-~- tive system.
FIG. 4 illustra-tes a diaphragm schematically showing such a lag or delay in the mechanical operative system.
A displacement quantity of the release plate 31 is given in EV value by the axis of or~inate and a time required for _ _ stopping down is giv~n by the axis of abscissa.

37~2 1 When a relative linear relationship is given between the displacement quantity of the release plate 31 and the diaphragm value obtained from stopping down ~y said dis-placement quantity, variation in diaphragm values depending upon the displacement quantities o~ the release plate 31 is not always uniform due to various ~actors such as a biasing force of the spring normally striving to urge the diaphragm blades back to their fully openea positions, inertia and frictional loads of the respective operative members. Thus, the lenses are practically classified into three types, i.e., a high speed lens M, an average speed lens N, and a - low speed lens ~. FIG. 4 -shows the respective characteristic `~- lines of these three types of lensesO Strictly, a variation of speed appears in movement of the release plate 31 itself during a period from start to stop thereof and particularly the release plate 31 moves at a low speed immediately after its start. However, such variation is negligible relative to the automatic diaphragm control operation by the release plate 31 as a whole, since it is during said preliminary displacement that such speed variation occurs and has little influence upon the cohtrol result even when this is approximately looked upon as a linear variation.
Therefore, tendencies of the respective lenses of three types are linearly shown. A straight line e~tending in parallel to the axis of abscissa indicates the preliminary aisplacement quantities Lv of the release plate 31 until the diaphragm blades reach their positions corresponding to the fully opened diaphragm values of the respective lenses. With respect to the lens M in the dia~ram, if the release plate 31 is supplied with a stop signal at a 1 moment of a time Ml elapsing after the release plate 31 has started, the diaphragm blades are actually stopped at a later moment M~. Similarly, with the lens N~ if the release plate 31 is applied with a stop signal at a moment Nl, the diaphragm blaaes are stoppea at a later momenk N2 and, in the case of the lens a, the diaphragm blades are stopped at a later moment ~2 with a stop signal applied to the release pla~e 31 at a moment ~1' Accordingly, no matter which type ~he lens belongs to, there occurs a time delay Td from application of the stop signal until the diaphragm blades actually stop. This means that to stop the diaphragm ~~ blades exactly at the moment corresponding to the desired diaphragm value, said stop signal must be applied to the release plate a moment earIier than the desired moment by such time delay Td due to the mechanical system or it would result in a stoppiny down in excess of the extent required for automatic diaphragm control. In other words, the dif-ferent lenses stop down different amounts after application of the stop signal.
The present invention proposes a countermeasure to this problem, too.
Referring again to FIG. 4, the quantity of stopping down achieved during the time delay Td due to the mechani-cal operative system depends upon the type of lens and ~_ 25 such quantity can be compensated for by the corresponding displacement quantity of the release plate 31 as follows:

Lens M .......... ..Lvm;
Lens N .......... ~. Lvn; and 30 Lens ~ ... ,...... ..Lv~.

~o~

1 It will be understood that the higher the speed of operation the lens has, the larger the quantity of stopping down made after application of the stop signal.
Now, setting the circuit in the camera body for genera-tion of the stop signal on the basis of the lens N havingthe average speed of operation, .i.e., so that said circuit yenerates the stop signal earlier by a quantity :Lvn with respec~ to the displacement quantity of the release plate 31, would result in actual quantities of stopping down excessive by Lvn -.Lv~-or the lens ~; and insufficient by Lvm - Lvn for the lens M.

Thus, the corresponding errors of diaphragm control would prevent achievement of the proper exposure. Also uniformly setting Lv = Lvn on the basis of said preliminary displace-ment quantity Lv depending upon the fully opened diaphragm value of the lens N having the average speed of operation would result in diaphragm control errors corresponding to said deviations even when the lenses.having the same fully opened dîaphragm value, so far as their speeds or operation are different due to the mechanical constructions peculiar to these lenses. Accordingly, the errors in quantities of ~ stopping down corresponding to the respective time delays --- 25 must be compensated for independently of the gradient of the characteristic line by setting the preliminary displace-~ ment quantities taking into consideration the time delays due to the mechanical systems of the respective types of lens as follows:

Lv = Lvm for the lens M;
Lv = Lvn for the lens N; and Lv = Lva for the lens ~.

~37-1 FIG~ 6 shows the interconneccion between diaphragm control magnet EEmg and release plate 31. Release plate 31 is guided by means not shown to move straight in accordance with movement Q~ the pin 13 working in the camera body side. The pos;~ion of a stop 40 in the path of release plate 31 varies ~rom lens to lens and determines the Lv value of the particular lens. Release plate 31 has teeth that mesh with -teeth on a spur gear 41. An annular membex (blade actuating r~ng 11) incorporating a spur gear 41 and a ratchet 4~ is guiaed for rotation by an annular guide member within the lens housing. The center of rota-~~~ tion of said annular member ;s indicated with a reference number 43 in ~IG. 5. Sai~ annular member having spur gear 41 and a ratchet 42 is provided with many small holes for pulse counting. Said holes are arranged along the circum-ference with the center 43 of rotation as its centex. A
displacement transducer in the form of a photo coupler PC
consists of a light emitting diode LED and a photometric element PE' positioned opposite to each other. The holes in the annular member pass in an arcuate row between the light emitting diode and the photometric element PE'.
When the ratchet 42 is moved by Lu~aL~G~ of the release plate 31, pulse signals proportional in number to the angular displacement of the annular member are generated by the rotation of said ratchet 42. These puls~ signals are applied to a pulse counter 54. In an analog indication of the angular displacement as desired, the output of counter 54 could be applied ~o au A-D converter 55. Either way, a 5l~
proportional to Av' is derived from pulse counter 54, and carries out diaphragm control action through the comparison ~3~-1 circuit. A pawl 44 prevents rotation of ratchet 42 in a countercloc~w;se direction as viewed in FIG. 6 and therefore also corresponding rotatio~ of spur gear 41 and release plate 31 during the automatic exposure and shutter release operation. When the shut~er is reset for ~he next photo-graph, pawl 44 is disengagea ~rom ratchet 42 to permit release plate 31 ~o return to stop 40. Pin 13 and release plate 31 are located in the lens, and spur gear 41, ratchet 42, shaft 43, and pawl 44 are locatea in the camera body.
A ratchet advancing tooth 45 is located in ~he camera body with magnet EEmg. Tooth 45 is mounted on the end of a ; magnetic pivot arm 46 biased into engagement with ratchet 42 by a spring 47. Magnet EEmg is wrapped around an armature 48 in proximity to pivot arm 46. Diaphragm control circuit Cl~ includes a switch 49 and a battery 50 in series with magnet EEmg. Switch 49 is opened and closed responsive to'comparator C14. When switch 49 closes, as shown in FIG. 6, pivot arm 46 is drawn against armature 48, thereby disengaging tooth 45 from ratchet 42. ~en switch 49 opens, spring 47 pulls pivot arm 46 away from armature 48, thereby driving tooth 45 against ratchet 42 to advance it one incremen~. Switch 49 is actuated by a relay control 52, such as a solenoid, which is driven by a pulse generator 53. Each time a pulse is supplied to relay control 52 by pulse generator 53, switch 49 opens to advance ratchet 42 one increment. Pulse generatox 53 begins sending pulses to relay control 52 when the shutter release-is actuated and . stops sending pulses to relay control 52 when comparator C13 lndicates equality between the two signals applied to its inputs. Accordingly, displacemcnt of ratchct 42, and thus bl~de actu~ting ring 11, is arrested responsive to comparator Cl3'~ wllen the t~o,signals applied to its in~uts are e~ual.

~ ~L9~371~:

To illustrate l10W the quantity of preliminary dis~
placement Lv can compensate for -the charac-teristics of.dif-feren-t lenses, assume -tha-t a lens M is displaced more than a reference lens N af-ter a stop signal is generated by a quantity ~Lv = Lvm - Lvn. If such displacement aLv cor-responds to an angular displacement of three holes on the annular member, stop 40 is so positioned that for lens M
three more holes on its annular member pass photocoupler PC
before the diaphragm blades protrude into the opening of the annular member than for lens N. Stated differently, if 30 holes on the annular member of lens N pass photocoupler Pc as the diaphragm stops down from the maximum value to a given smaller value, stop 40 on lens M would be so posi-tioned tha-t 27 holes on its annular member pass photocoupler PC as the diaphragm stops down from the maximum value to the same given value, assuming -the charac-teristics of lenses M and N
are otherwise identical. ~lthough the same number of holes on the annular member pass photocoupler in bo-th cases, for lens M fewer pass after the diaphragm blades protrude into the opening of the annular member, i.e., after rotation of the annular member changes the diaphragm value. The o-ther errors referred to above are compensated for in similar fashion, i.e., fewer or more holes on -the annular member pass photocoupler PC before the diaphragm blades protrude into the opening.of the annular member depending upon the extent of correction, i.e~, compensation to be eEfected by the position of stop 40. Since the initial rotation of the diaphragm actuating ring, which corresponds to the pre-liminary displacement prescribed for the particular lens, does not resul-t in any reduc-tion of the aperture value, a number of the pulses stored in the counter do not correspond to actual reduction of the aperture value, but instead cor-respond to the characteristics of the particular lens, thereby providing compensation for di.f:Eeren-t lens characteris-tics from lens to lens.

With reference to equation 4 above and Fig. 2, the 7~%

value of Av' produced by generator C10 is already compensa-ted for by ~v. Thus, in contrast to the arrangement dis-closed in Japanese application serial No. 56(1981)-10722 published August 26, 1981, B ' rather than B can be used for comparison in comparator C11, and it is not necessary to process Amax in an ari-thmetic circui-t wi.th the signal generated by the displacement transducer in the lens housing, because ~Av, ~min, and ~ Amax are all accounted for in the preliminary displacement. Thus, by virtue oE the preliminary displacemen-t, which does not change the aperture value, the signal produced by generator C10 is compensa-ted for devia-tions of -the lens from the reference lens, i.e., ~ Av, ~Amin, and ~ Amax, as well as other aspects if desired.

Wi-th respect to the camera and the objective accord-ing to the automatic diaphragm control mode which is incor-porated with the compensation for a difference in the fully opened diaphragm values of the xespective lenses inter-changeably mounted on the camera and the compensation for a difference in -the speeds of stopping down operation thereof, a preferred embodiment of the lens mounting arrangement by which the signal characterizing individual lenses is trans-mitted from the lens to the camera body is illustrated by Fig. 5.
~ eferring to Fig. 5, a portion designated by reference symbol CM corresponds to a mount on the camera for mounting of an objective while a portion designated by reference symbol LM corresponds to a mount on the lens.
3~ Both the mount CM`on the camera body and the moun-t LM on the lens are shown at their surface along which they are mutually abutted, namely, the mount CM is shown as seen from the camera front while the mount LM is shown as seen from the rear side of -the lens. Both the mounts are 71~;2 1 provided with a pair of opposed contacts by which ON and OFF
signals are transmitted in the form of binary codes or elec-tric current is transmitted ~epending upon an electrical factor such as resistance value which is, in turn, determined by the fully closed diaphragm value. According to the present invention, there are pr~vided a pair of contacts 19 and 91 through which the informa-tion on the fully closed diaphragm value depending upon the individual interchangeable lens mounted on the camera and o~ the automatic diaphragm control position (Au~o) det~rmined by said fully closed diaphragm value is transmitted from the lens to the camera ,-j body. It is through ~his pair o~ contacts that the ~Amin ~ signal determined by said fully closed diaphragm value is transmitted from the lens to the camera body. This pair of contacts constitutes a part of the fully closed aperture signal generating member C6 shown in FIG. 2.
As will be obvious from the foregoing detailed descrip-tion, the present invention enables the operation of stopping down at the highest precision ~y automatic diaphragm control through the operation of stopping down which already includes therein the compensation by a simple mechanism of both the illumination intensity error in the film plane appearing due to the illumination intensity variation and the illumina-tion intensity error due to the position of the photometric ~5 element depending upon individual interchangeable lenses mounted on the camera. The provided mechanism serves to stop down with a ccmpensating preliminary displacement taking no part in the actual stopping down effect for the interchangeable lenses on the other hand. Concerninq said preliminary dis-placement quantity, a delay occurring in the mechanical ~907~
~~2-1 operation determined by the different speeds of stopping down, which depends~ in turn, upon the indiviaual lens interchangeably mounted on the cam~ra, is also considered and thereby said preliminary displacement quantity is further finely adjusted so that the automatic exposure control can be achieved with an extremely high precision including therein the effective compensation of the deviations caused by all the factors depending on the individual lenses. In spite of achievement of such high precision exposure control, the presen~ invention advantageously simplifies the mount construction along which-the interchangeable lens is coupled ~ to the camera body, since it is unnecessary, in accordance `- with the present-invention, to transmit the information signal related to the fully opened diaphraym of the respec-tive lens from the latter via the lens mount to the camera body so as to be incorporated into the regulating factors for the exposure control circuit. The exposure control circuit is also simpliied in its construction according to the present invention; specifically, no means is required to change over the fully opened diaphragm signal in oxder to compensate the change of F value when a zoom lens accompanied with said change of F value is mounted on the camera. The present invention accordingly provides the desired inter-changeable lens single-lens reflex camera of automatic 2S exposure control type, which is simple as well as compact in its overall construction, and obtainable at a low cost and almost trouble-free.

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A camera comprising:
a displaceable actuator;
a diaphragm adjustable between a maximum aperture value and a minimum aperture value responsive to displacement of the actuator;
means for generating a first signal representative of the displacement of the actuator;
means for generating a second signal representative of the desired aperture value of the diaphragm for correct exposure;
means for comparing the first and second signals;
means for displacing the actuator responsive to the comparing means to stop down the diaphragm from the maximum aperture value toward the minimum aperture value until the first and second signals assume a predetermined relationship; and means for maintaining the diaphragm at the maximum aperture value during an initial portion of the displacement of the actuator.

2. The camera of claim 1, in which the diaphragm comprises a plurality of blades continuously rotatable responsive to displacement of the actuator, the blades together defining an opening decreasing in size during actuator displacement and the maintaining means comprises a ring masking the diaphragm blades during their rotation responsive to the initial portion of the displacement of the actuator, the ring defining the maximum aperture value.

3. The camera of claim 1, in which the predetermined relationship between the first and second signals is equality.

4. The camera of claim 1, in which the camera additionally has a lens for receiving light passing through the diaphragm and the first signal generating means comprises a photometric element positioned to receive light passing through the lens, the photometric element producing a light quantity representative signal and means for logarithmically compressing the light quantity representative signal, and means for modifying the compressed signal to reflect the desired shutter speed and film sensitivity.

5. The camera of claim 4, additionally comprising a camera body and a lens housing, the diaphragm, lens, and second signal generating means being disposed in the lens housing.

6. A camera comprising:
a camera body;
first and second lens assemblies interchangeably insertable into the camera body, each lens assembly having a displaceable actuator, a diaphragm adjustable between a maximum aperture value and a minimum aperture value responsive to displacement of the actuator, and means for generating a first signal representative of the displacement of the actuator;

means in the camera housing for generating a second signal representative of the desired aperture value of the diaphragm for correct exposure;
means for comparing the first and second signals;
means for displacing the actuator responsive to the comparing means to stop down the diaphragm from the maximum aperture value toward the minimum aperture value until the first and second signals assume a predetermined relationship; and means in the second lens assembly for maintaining the diaphragm at the maximum aperture value during an initial portion of the displacement of the actuator.

7. The camera of claim 6, in which the comparing means and the displacing means are located in the camera body.

8. The camera of claim 7, in which the initial portion of the actuator displacement compensates for deviations in the diaphragm value, .DELTA.Av, the maximum aperture value, .DELTA.Amax, and the minimum aperture value, .DELTA.Amin, of the first lens assembly from the second lens assembly.

9. The camera of claim B, in which the initial portion additionally compensates for differences in the actuator stopping distance between the first and second lens assemblies.

10. The camera of claim 9, in which the second signal means includes a photometric element for receiving light passing through the lens assembly and the initial portion additionally compensates for the illumination intensity error due to the position of the photometric element.

11. The camera of claim 10, in which the initial portion additionally compensates for the illumination intensity error in the film plane.

12. An interchangeable lens assembly for a single-lens reflex camera of interchangeable lens type, said inter-changeable lens comprising an arrangement such that a quantity corresponding to a total deviation of fully opened diaphragm value depending on an individual interchangeable lens assembly, light intensity error in the film plane associated with this fully opened diaphragm value and light intensity error due to a position of a photometric element from a fully opened diaphragm value and the corresponding error peculiar to a reference lens is compensated by a part of a mechanical opera-tive system adapted to transmit an operation of a diaphragm driving member in the camera body occurring under control of an exposure control circuit to diaphragm blades in the lens in the form of a quantity of preliminary displacement pre-sented by said part of the mechanical operative system that takes no part in a light quantity control effected by opera-tion of stopping down.

13. An interchangeable lens assembly for a single-lens reflex camera of interchangeable lens type, said inter-changeable lens comprising an arrangement such that a quan-tity corresponding to a total deviation of fully opened dia-phragm value depending on an individual interchangeable lens assembly, light intensity error in the film plane associated with this fully opened diaphragm value and light intensity error due to a position of a photometric element from a fully opened diaphragm value and the corresponding errors peculiar to a reference lens is compensated together with a diaphragm blade stoppage error corresponding to an actua-tion lag due to a construction of a mechanical operative system adapted to transmit an operation of a diaphragm driv-ing member to diaphragm blades, said actuation lag occurring during such transmission, by a part of said mechanical opera-tive system in the form of a quantity of preliminary dis-placement presented by said part of the mechanical operation system that takes no part in a light quantity control effected by operation of stopping down.