CA1150556A - Method and apparatus for selective positioning of spectral filter during exposure control - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Method and apparatus using shutter blade and photocell lens arrangement for automatically controlling exposure of a photographic film by evaluating selected spectral scene light frequencies during certain ambient light portions of an exposure interval and evaluating additional spectral frequencies during a flash portion of the interval.

Description

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~253 BACKGROUND OF THE INVENTION
This invention relates generally to the photographic field and, more particularly, an improved method and exposure control system for automatically and selectively controlling the filtering of light incident upon a photoresponsive element during exposure.
Automatic light responsive control systems are well known in the photographic arts. Essentially, these systems evaluate scene brightness levels of illumination for controlling exposure parameters, including effective aperture size and exposure interval, as a function of scene brightness evaluated against the sensitometric characteristics of the film being used. Typically, scene brightness evaluation is performed with light-measuring circuits including one or more photoresponsive elements.
One such automatic exposure control system employs scanning type shutter blades. Exemplary scanning shutter blades usable in exposure control systems are generally disclosed in U.S. Patent No. 3,942,183, issued March 2, 1976, to George Whiteside; and U.S. Patent No. 4,104,653, issued August 1, 1978, to Bruce K. Johnson et al., all of which are presently assigned with the present application. As described in these patents, there are cooperating pairs of primary and secondary apertures formed in the shutter blades.
These pairs of apertures cooperate respectively for blocking and unblocking the passage of light through an exposure opening to a film plane and through a photocell opening to a light sensing or photoresponsive cell used for controlling blade : , j . ,~

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positioning. During the exposure cycle, the secondary apertures operate in conjunction with the photocell and a control circuit to define both the aperture values achieved and the exposure interval as a function of the amount of light received through the secondary apertures. In such systems, photoresponsive elements of the silicon type are commonly used because they, among other things, have excellent long term stability and linearity of output signal with input light power changes.
For optimizing the quality of the resultant photographs when using automatic exposure control systems, such as the type noted, it is known to employ spectral correction filters to correlate the spectral sensitivity curve of the photoresponsive element more closely with that of the photographic color film. Without such a filter, the photocell would react to the light frequencies, such as infrared (IR), and cause the control circuit to terminate exposure earlier than desired. This is especially the case when the photocell is of the silicon type, because such a photocell tends to be red (IR) sensitive. For providing the desired correction, a spectral correction filter is interposed in the photocell's optical path, for example, ` as described in U S. Patent No. 3,903,413, issued on September 2, 1975, to Monis Manning; and commonly assigned ~5 with the present application. This patent discloses use of a silicon photodiode, sensiti~e to radiant energy between about 350 nm and 1200 nm, whereas the sensitivity of typical color photographic film is confined to the visible ``` region of the spectrum, i.e., from about 400 nm to about ~ ~ 700 nm. ~se is made of a spectral correction filter with peak absorption in the near-infrared region (70~-1200 nm) and high transmission in the visual region to correct or generally match the spectral response of the photocell in relation to the film. This matching of sensitivities is particularly useful in camerasemploying diffusion transfer photographic processes of the so-called "instant photography"
type where errors in the exposure cannot be later compensated for as is possible with film subsequently developed in a photographic laboratory.
While use of infrared filters serve satisfactorily, complications can arise when reflectivities of different objects in photographic scenes exhibit widely disparate values, for example, where the exposure of the subject's facial skin is adversely affected because of the widely disparate reflectivities of the surrounding clothing or other objects, particularly in close-up situations. Partly as a result of this, it has been found advantageous to remove the infrared filter in flash exposure modes of operation.
Consequently, although retention of spectral correction filter in the photocell's optical path has been practiced during both ambient and artificial illumination modes, as disclosed in U.S. Patent No. 4,040,070, issued on August 2, 1977, to W. Hochreiter et al., a spectral correction filter (possibly an IR) is removed from the photocell's optical path when the flash mode is desired.
This removal is achieved, upon attaching a flash unit to the camera, by actuation of a relatively complicated mechanical arrangement which swings the filter out of the optical path.
Still other known prior art is described in U.S.
Patent No. 3,468,228, issued on September 23, 1969, to 55~

Howard G. Rogers, which provides automatic sequer~tial positioning of a pair of dual filters over photocell and exposure apertures to attain a color balanced exposure of photosensitive material.
Approaches have been developed which represent substantial improvements over those known in the prior art. In this regard, exposure control systems for automatical]y controlling scene light intensity and spectral filtering thereof during an exposure interval as a function of blade mechanism positioning which itself is a function of the scene light intensity have become known. More specifically, they effectively remove a blocking infrared filter relative to the photocell detector during a portion of the exposure interval. These systems operate extremely satisfactorily.
SUh~RY OF THE INVENTION
-In accordance with the present invention, an improved method and .; apparatus employing photocell lens and shutter blade arrangement for automatically controlling exposure of a photographic film in accordance with selected spectral scene light frequencies during a predominantly ambient portion of an exposure and additional or other spectral frequencies of scene light during a flash portion of the exposure.

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In the illustrated embodiment, there are provided means for mounting photographic film material at a given focal plane and a light exposure opening for allowing passage of light to the film and to detecting means for evaluating scene light; a flash means for illuminating the scene; and a blade mechanism mounted for displacement between first and second positions for defining an exposure interval and both changing primary aperture values over the exposure opening and changing secondary aperture values over the detecting means as the mechanism moves toward its second position. Selectively actuatable drive means are provided for initially displacing the blade mechanism from the first position toward the second position, and in response to the amount of scene light detected by the detecting means for firing the flash means and for also returning the blade mechanism to the flrst position.
~ In one embodiment, the filtering means is a ; spectral filter positioned relative to the blade mechanism and a photocell of the detecting means serves to substantially block transmission of preselected scene light frequencies to a preselected area of the detecting means and to further define an unfiltered area substantially allowing transmission ~ of a broad range of scene light to the detecting means. During i blade mechanism movement from the first or scene light blocking condition toward a second scene light admitting position, secondary apertures sweep past the spectral filter in such a fashion as to initially block passage of scene light thorugh the unfiltered portion while permitting passage of and filtering o~ such scene light by the spectral filter.
; 30 ~s the ~lades continue to sweep toward the second position, 55~

the secondary apertures then become positioned to substantially block transmission of scene light through the filtered portion while simultane-ously allowing scene light passage through the ulfiltered area. Advantag-eously, since the blade scan is terminated early under moderate-to-high scene light levels, spectral filtering, such as IR, is provided for the predominantly ambient exposure while under lower light levels, where the flash provides a significant contribution~ the IR frequencies are evalua-ted by the system.
Among the objects of the invention are, therefore, a method of providing an improved photographic exposure control process; a method of providing improved flash photography; and the provision of photographic apparatus having an improved exposure control system including a spectral filter and blade mechanism which cooperate to effect selective filtering of the scene light admitted to the photoresponsive element as a function of the scene light.
According to a first broad aspect of the present invention, there is provided in a photographic apparatus having means for directing image forming light rays from a scene to a photographic film material mounted at a given focal plane, means for evaluating radiation from said scene during an evaluation period, means for unblocking and blocking passage of said image forming rays to said focal plane, and means responsive to said evaluating means for controlling said unblocking means to define an evaluation period, the improvement wherein said evaluating means includes:
means for evaluating scene radiation along a first path for substan-tially precluding evaluation of selected spec~ral frequencies and along a second path substantially permitting evaluation of said selected frequen-cies and additionally including means for alternating between said paths during said evaluation period.
According to a second broad aspect of the present invention, there is provided in a photographic apparatus having means for directing image forming light rays from a scene along a given path to a photographic film materlal mounted at a given focal plane, means for evaluating radiation from said scene during an evaluation period, means for unblocking and blocking said path, and means responsive to said evaluation means for controlling said unblocking means to define an exposure interval, the improvement wherein said evaluating means includes: means responsive to operation of said unblocking and blocking means for automatically sub-stantially precluding evaluation of selected spectral frequencies during at least one portion of the operation of said unblocking and blocking means while substantially permitting evaluation of said selected frequen-cies during at least another portion of the operation of said unblocking and blocking means.
According to a third broad aspect of the present invention, there is provided a method of exposing photographic film comprising the steps of:
initiating a scene light evaluation period by directing image forming scene light rays from a scene to be photographed to photographic film material located at a given focal plane; evaluating selected spectral frequencies of the scene illumination along a first path by essentially excluding predetermined frequencies at least during a portion of the evaluation period; evaluating selected spectral frequencies of the scene illumination along at least a second path by including the predetermined frequencies during another portion of the evaluation period; and blocking passage of image forming light rays from the scene to the film in response to a predetermined value of evaluated scene radiation to thereby terminate the evaluation period.
The invention will now be described in greater detail with reference : to the accompanying drawings, in which:
.~` FIGURE 1 is a diagrammatic front view in elevation depicting a photographic camera incorporating the improved exposure control system of this invention including a blade mechanism illustrated in a closed condition;
` 30 FIGURE 2 is an elevational view diagrammatically depicting the blade - mechanism of FIGURE 1 in an initially open condition during operation;

~ -6a-;56 FIG. 2A is an enlarged fragmentary view illustrating in greater detail the cooperative relationship of the secondary sweep apertures with respect to the spectral filter when in the position shown in FIG. 2;
FIG. 3 is a side elevational view diagrammatically showing the improved exposure control system of this invention;
FIG. 4 is a view similar to FIG. 2 but showing the blade mechanism of FIG. 1 in a more open arrangement;
FIG. 4A is an enlarged fragmentary view showing the secondary sweep apertures in a position relative to the spectral filter when in the position shown in FIG. 4;
FIG. 5 is a view similar to EIG. 4 but showing the blade mechanism in its fully open arrangement;
FIG. 5A is an enlarged fragmentary view showing the secondary sweep apertures in a position relative to the spectral filter when in the position shown in FIG. 5;
FIG. 6 is a diagrammatic view depicting -the relationship of the blade mechanism and spectral filter of the improved exposure control system; and FIG. 7 is a diagrammatic perspective view showing the relationship of the masking members to the spectral filter.
DETAILED DESCRIPTION
Referring now to FIG. 1, it can be seen that the improved exposure control system of this invention is contained within a housing of photographic camera 10.
Included within the camera housing 10 is a rear b].ock casting 12 constructed to support components of the exposure control system. A light exposure aperture 14 --7~

;b~3 556 is centrally formed in the casting 12 and defines the maximum available exposure aperture of this control system as well as allows passage of scene light to a photographic film unit (nct shown) of a film pack 16.
Examples of such a film pack 16 are described in United States Patent Nos. 3,543,662; 3,705,542; 3,748,984 and 3,779,770. Each of the film units of the pack 16 is successively positioned at the focal plane F of the camera.
Mounted on a front wall of tha housing 12 is a taking or objective lens 18 of the fixed focus type. The taking lens 18 focuses 10 the image carrying rays from the scene to be photographed along an exposure path to a mirror 20. Although the described lens 18 is illustrated as a fixed focus ~ype, an adjustable lens assembly is also contemplated as a substitute therefor. From the mirror 20, the rays are reflected to the uppermost film unit o-f the film pack 16. Additionally, a viewing window 22 is located in the front face of the camera housing 10 and operates in conjunction with a viewing system`24 for permitting viewing and framing of the scene to be photographed by the operator.
Control of the exposure path is provided by the improved exposure control system 26.
Although the above exposure control system is described for use with photographic`cameras of the non-reflex type, the intended scope of this invention is by no means so limited. Accordingly, cameras of the well-known reflex type, such as described in United States Patent -55~

No. 3,672,281, entitled "Reflex Camera", by E. H. Land, commonly assigned herewith, may be equally suitable for embodying the exposure control system of this invention.
Reference is now made to FIGS 1-5 for better showing the constructional and positional arrangement of the exposure control system 26. Included in this system 26 is a blade mechanism having overlapping shutter blade elements 28 and 30. With particular reference to FIGS. 1 and 6, the shutter blades 28 and 30 are supported in the block casting 12 intermediate the objective lens 18 and the light entering exposure opening 14. A pair of scene light admitting primary apertures 32 and 34 are provided, respectively, in the blade elements 28 and 30. In use, the primary apertures 32 and 34 coincide and overlap progressively over the light entering exposure opening 14 to define progressively increasing primary aperture values as a function of blade positioning during an exposure interval.
The shutter blades 28 and 30 additionally include a pair of secondary apertures, each consisting in the illustrated embodiment of a plurality of apertures such that the blades have a plurality of sets of sweep secondary apertures generally indicated by reference numerals 36, 37, 38, 39, ~0. In operation, the sets of secondary apertures 36, 37, 38, 39, 40 move in correspondence with the primary apertures 32, 34 to progresslvely coincide so as to define progressively varying and distinct sets of secondary aperture values as a function of blade positioning during exposure. As will be explained in greater detail, the sets of secondary sweep apertures 36-40 cooperatively coincide with each other and with a spectral filter 41 (FIGURF, 6) to effectively and automatically control the intensity and spectral frequency of scene light passing to a light detecting station 42 as a function of blade positioning during the exposure interval. This light detecting station 42 includes a photoresponsive device or photocell 44 aligned with a photocell light entry window (not shown) in the housing 10. Preferably, the photocell 44 is of the silicon photodiode type. Also, included in the light detecting station 42 is a control circuit (not shown~ for collectively operating with the photocell 44 for terminating the exposure interval as a function of time integration of the intensity of light incident upon the photocell 44 as permitted by the overlapping sets of photocell sweep apertures 36-40.
Since the light detecting station 42 does not per se form an aspect of the invention, only those details needed for an understanding of the present invention will be given. Also, for greater details of the construction and operation of the blade mechanism, reference is made to commonly assigned United States Patent No. 3,942,183. Since the blade mechanism does not by itself form an aspect of the invention, only a description of its construction necessary for a complete understanding of this invention will be set forth. In this regard, it will be understood that distal ends of the shutter blades 28, 30 are pivotally connected ~.$~

to distal ends of a walking beam 46. The walking beam 46 is pivotally connected to the block casting 12 by a pivot pin 48 and its distal ends have pin members extending through respective circular openings in the respective blade elements which pins slidably engage respeckive arcuate slots 49 formed in the rear casting 12 for prohibiting shutter blade disengagement during exposure control operations.
Displacemen-t of the shutter blades 28, 30 relative to each other and to the light detecting station 42 and to the spectral filter 41 is provided, in part, by a tractive electromagnetic device or solenoid 50. Such solenoid 50 includes an internally arranged and movable cylindrical plunger unit 52 which retracts upon solenoid energization. This plunger unit 52 is affixed to the walking beam 46 by means of a pivot pin or stud. Thus, longitudinal displacement of the plunger unit 52 is effective to rotate the walking beam 46 about the pivot pin 48 and in so doing cause appropriate displacement of the shutter blades 28, 30; as will be described more fully.
For continuously urging the primary apertures 32, 34 and the sets of secondary sweep apertures 36-40 to positions defining their effective apertures, there is provided a biasing spring 54. One end of the spring 54 is affixed to the block casting 12 while its opposite end is attached to the walking beam 46. As should be ~ understood readily, the exposure control system 26 is - also applicable to photographic systerns wherein the blades 28, 30 are spring biased to a norrnally closed position.

For purposes of battery power conservation, it is undesirable to have the solenoid 50 continuously energized to maintain the shutter blades 28~ 30 in the scene light blocking conditions (FIGURE l) when the camera is not in use. Towards this end, there is provided a latch mechanism (not shown) operable automatically at the end of each exposure for latching the walking beam 46 in the scene light blocking position.
Thus, the solenoid 50 is deenergized when the blades 28, 30 are in the scene light blocking condition. Unlatching of the latch mechanism commences upon exposure. Details of this latching mechanism including its operation do not per se form an aspect of this invention; there~ore, reference is made to United States Patent No. 4,040,072, issued August 2, 1977, and assigned in common herewith for a more complete description thereof.
Reference is now made to the flash strobe unit 56 of the present embodiment. In essence, the electronic flash strobe unit 56 is cooperatively associated with the photographic camera appara~us to contribute a predetermined proportion, i.e., fill flash of the scene light admitted by the shutter blade mechanism to expose the film in a manner to be subsequently described. Since this type of fill flash does not per se form an aspect of the present invention, only those details necessary for an understanding of the present invention will be described. The electronic flash strobe unit 56 is affixed to an upper surface of the .
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camera housing 10. Included in the unit 56 is a flash discharge tube 5~ located in a suitable reflector 60 behind a lens 62. A quench tube (not shown) is provided for interrupting the flash discharge of the flasn discharge tube 58 and elcctric power for the electronic flash strobe unit 56 is provided by a battery (not shown) carried in the film pack 16.
The output signal from a light integrator circuit ~not shown) of the scene light detecting station 42 is directed to three level detector circuits (not shown) which all may be of a well-known design, such as a Schmitt trigger. The output from one of these level detectors controls a flash fire trigger circuit (not shown) of the electronic flash unit 56.
The second level detector is effective to control the energization of the solenoid 50, and the third level detector is effective to control a flash quench circuit (not shown).
For purposes of illustrating operation of the flash unit 56J
the level detector which controls energization of the solenoid (to close the shutter) is configured to trigger at 1.0 volt, which is a normalized value representative of a select or optimum film exposure value for a predetermined film speed; the level detector for controlling the quench trigger circuit is set to trigger at 1.2 volts; and the level detector for controlling the flash fire trigger circuit is set to trigger at 0.75 volts.
These values will, however, later serve to better describe the present ' invention. Also, a flash time delay circuit (not shown), which receives an input signal upon the deenergization of the solenoid 50, is included to provide a time delayed flash fire signal operative to trigger the flash under very low ambient light conditions as later explained in detail.
The time delay provided by the flash delay circuit may be in the order of 65 + 4 msec.
Operation of a camera actuator button (not shown) powers up the camera 10, enables the strobe unit 56 for subsequent firing and releases the shutter latch mechanism to allow shutter blade movement to commence the exposure cycle. More specifically, the shutter blades 28 and 30 move in opposite directions from the scene light blocking condition of FIGURE 1 toward the maximum primary aperture value shown in FIGIJRE 4. Thus, the effective aperture area over the light entering exposure opening 14 is enlarged progressively.
Simultaneously with enlarging primary aperture values, the secondary photocell sweep apertures define a corresponding progressively enlarging secondary effective aperture opening over the light detecting station 42. In this embodiment, the effective photocell sweep aperture value defined by the overlapping secondary apertures tracks ahead of or leads the effective scene light admitting primary aperture defined by the overlapping primary apertures 32 and 34 to anticipate in a well-known manner for the additional scene light admitted to the film plane during the finite time required to drive the shutter blades ~. `. '' .

28, 30 from the scene light unblocking arrangement of FIGURES 2 and 4 back to the scene light blocking arrangement of FIGURE 1, as is more fully described in United States Patent No. 3~896,458, entitled "Automatic Exposure Control System", issued July 22, 1975.
The photocell 44 provides a time varying response representative of the time integration of the scene light intensity incident to the photocell. Under conditions of moderate-to-high scene light, when the integration signal reaches 0.75 volts, the flash level detector triggers firing of the flash discharge tube 58 in a well-known manner. Assuming the photographic subject is within the effective range of the flash, there will be an immediate and substantial increase in the reflected scene light to which the detecting station 42 will respond to provide the required voltages to trigger the second and third level detectors for respectively effecting re-energization of the solenoid 50 and quenching the flash tube. Thus, the shutter blades 28, 30 move back to the scene light blocking arrangement as shown in FIGURE 1, and the exposure interval is terminated.
In regard to the exposure control, it should be noted that with diminished intensity of scene light, the flash unit is fired at later times such that the flash is fired at larger primary and secondary aperture values. Moreover, under conditions of extremely low or negligible ambient scene light intensity, the light integrator circuit will not provide a 0.75 volt output response prior to the expiration of the 65 * 4 millisecond flash time . : , . ~, . .

delay. For these conditions, a signal is transmitted by the flash delay circuit at the expiration of the noted time delay to effect flash firing. Moreover, in the event that there is neither sufficient available ambient scene light and/or artificial flash light for the output signal from the light integrator to reach 1 volt, the shutter time out circuit operates to energize the solenoid 50 and thereby limit the maximum exposure interval to, for example, 100 milliseconds. In this manner, the camera apparatus of this invention is provided with an electronic flash together with means for controlling the energization of the electronic flash to assure that a predetermined proportion of a select film exposure value will be attributable to the artificial light provided by the electronic flash at least when a subject is within the effective camera-to-subject distance range of the flash.
Reference is again made to FIGS. 1-6 for better describing the structural and functional interrelationship between the shutter b]ades 28, 30, spectral filter 41 and the photocell 44.
With particular reference to FIG 6, the photocell 44 is seen to include a photocell lens 64 and linearly spaced therefrom a silicon photocell detector 66 which produces a current output when subjected to incident radiation. In the illustrated embodiment, the photocell lens 64 is of the defocusing type. The photocell lens 64 is in optical alignment with the photocell light entry window (not shown) in the front face of the camera housing lO and receives the scene light passing through the sets of secondary apertures. Positioned intermediate the photocell lens 64 and the silicon photocell detector 66 is the pair of scanning shutter blades 28, 30. Positioning of the shutter blades 28, 30 relative to the photocell lens 64 is carried out to insure that the secondary sweep apertures 36-40 direct preselected portions of spectrally filtered scene radiation passing through the filter 41 to the photodetector 66 for purposes subsequently explained.
For purposes of carrying out the selective attenuation of spectral energy, this embodiment has the rear face of the photocell lens 64 partly covered with a coating effective for blocking infrared radiation (IR).
This coating is in the form of an annulus, such as best shown in FIG. 6. Since the center portion 68 of the photocell lens 64 is unfiltered, it will allow I~ radiation to the photocell detector 66 as well as the visible spectral energy. The significance of this relationship in modifying exposure control will be explained subsequently.
It should be noted that the center portion 68 may also be provided with another lens (not shown) for further assisting in directing scene light to the photocell detector 66.
Referring back to the blocking IR filter 41, it is fabricated to attenuate spectral energy within the broad wavelength range to which the photocell detector 66 is sensitive (e.g., 360-1200 nm) and, preferably, to remove substantially all the spectral energy in the IR region (e.g., 700-1200 nm) of the photocell range. Thus, visible spectral energy remains after passing the IR filter 41. Control of the photometric response by selective filtering and nonfiltering of the radiation incident upon the photodetector .

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66 is accomplished by the unique cooperation between the photocell lens 64, spectral filter 41 and the sets of secondary sweep apertures 36-40.
Prior to describing the filtering opera~ion in S detail, it should be first explained that the novel arrange-ment automatically provides IR filtering of the photocell input at moderate-to-high light levels since the ambient contribution is most important under such conditions, but under lower light levels permits passage of, and evaluation of, the IR because the flash illumination is then of greater importance to the resulting photograph. Broadly, the secondary apertures in conjunction with the filter 41 provide means for substantially permitting transmission of selected frequencies during one portion of the blade scan and, hence, the exposure interval while precluding transmission of the same frequencies during another portion; at least when the scan reaches large aperture values under low light conditions. ~s shown in FIG. 2, the pairs of photocell sweep apertures 36, 37, during initial shutter blade sweep from the light blocking condition of FIG. 1 to the condition shown in FIG. 2, progressively cooperate to pass only scene light passing through the annular filter 41. The filter 41 acts, of course, to ` block the IR while the opaque portion of the shutter blades 28, 30 block passage of unfiltered light through the center portion 68. It is envisioned that this relationship of the shutter blades 28, 30 will be at positions corresponding to moderate-to-high ambient light conditions and correspond ` to primary aperture values less than their maximum. With the scene light being filtered by the IR filter 41, the potential of overexposing blue sky is eliminated. A ~lash will be fired during this exposure and the reflected light thereof evaluated in accordance with the invention without the benefit of IR radiation, however, since the flash contribution under these levels of ambient light is not controlling, the lack of precise flash accuracy is tolerated in favor of ambient control~
Under conditions wherein ambient light is very low, ~he photocell detector 66 in cooperation with the light integrating circuit reenergize the solenoid 50 at a later time to terminate exposure. Therefore, under low ambient light conditions, the shutter blades 28, 30 sweep beyond their position in FIGURE 2 and ultimately to the position shown in FIGURE 5, and in doing so the central secondary sweep apertures 38 progressively coincide over the unfiltered portion 68 to define sweep aperture values which allows transmission of infrared spectral energy to the photocell detector 66 as well as the visible spectral energy while the aperture values defined by the secondary sweep apertures 36, 37 eventually terminate. As a result, in moving from the blade position of FIGURE 2 to that of FIGURE 5, the spectral filtering is rapidly diminished, and in fact, eliminated by means of masking elements as explained below. Under the latter condition, the primary apertures 32, 34 define their maximum effective diameter.
Since the secondary sweep aperture value defined by the central sweep apertures 38 will, when in coincidence, overlie a portion of the annulus 41 and thereby allow -19~

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light to pass through ~he filter 41, the masking elements 70 (FIGS, 6 and 7) are provicled. These masking elemen-ts 70 may be connected to the camera housing 10, the le~s 64, or any camera portion so as to fixedly be in position to the light path to the photocell. In this regard, the palr of masking elements 70 essentially straddle the unfiltered central portion 68 and have their terminal ends with arcuate formations to match the curvature of such central portion. Thus, the masking elements 70 block filtered scene light passed through the filter 41 and the central sweep apertures 38 from reaching the photocell detector 66. The exposure control system 26 can also operate without the masking elements 70 since the effect of such slight blocking of the IR leakage on film exposure during transition can be minimized for practical purposes. Further, the filter 41 can also be constructed as a pair of annular segments mounted at the top and bottom of the lens 64 as viewed in FIG. 7.
Since, under high ambient light conditions, the - 20 blade scan is terminated early, only the sweep apertures 36 and 37 provide aperture values over the photocell.
Hence, the absorption filter 41 blocks, or precludes transmission of, IR radiation from the scene at such time. However, with lower ambient light levels, the secondary apertures 38 come into coincidence over the unfiltered opening 68 (while apertures 36 and 37 pass out of coincidence) as larger exposure values are formed.
Accordingly, the shutter blades 28, 30 move to the position shown in FIG. 4 where the filterless opening 68 is employed for transmission to the photocell. Consequently, ln the latter case, the scene light inc;dent upon the photocell 44 is selectively filtered to block IR during the initial portion of the displacement of the shutter blades 28, 30 or that is, an initial portion of the exposure lnterval and then becomes unfiltered as opening 38 coincide so that the photocell then responds to both IR and visible radiation during this subsequent portion of the displacement.
Hence, it should be understood that the filter 41 in conjunction with the blade mechanism provides means for automatically permitting transmission of selected frequencies of light to the sensing or detecting means during at least one portion of the displacement of the blade mechanism or, that is, one portion of the exposure interval while substantially precluding transmission of the selected frequencies to the sensing means during another portion thereof.
Consequently, in accordance with this invention when the flash unit 56 is fired in situations of somewhat low ambient scene light (where the flash contribution to the resulting photograph is predominant as compared to the ambient contribution), the shutter blades 28, 30 will, during scanning, be positioned during the strobe flash with apertures 38 in coincidence so that the IR filter 41 is not in spectral filtering relationship to the photocell 44. Thus, the photocell 44 is no longer blocked from receiving IR radiation. As a result, during the early stages of blade displacement, prior to the flash, only visible light will be incident upon the photocell while at the later stages, during flash operation both visible and IR radiation are evaluated such that the earlier mentioned difficulties encountered with flash firings will be substantially overcome. In this regard, objects viewed in the visible spectral region exhibit widely different light reflectivities while the near infrared region (e.g., 750-1200 nm) is characterized by more uniform re~flectivity for most common materials. Therefore, the IR reflectivity is much less dependent on the visible color (specific visible light absorption), and objects viewed by infrared are relatively independent of the reflectivity disparities earlier described. Thus, in scenes where differences in the visible reflectivities are present or which can be exaggerated by light sources such as flash bulbs or s~robes, it is highly desirable to evaluate the IR radiation because, with such IR radiation, there will be less reflectivity differences between, for example, a subject's facial skin and the surrounding clothing or other objects. This substantially minimizes the degree of under or overexposure in such situations. It is, therefore, apparent that under flash conditions with exaggerated scene differences in reflectivities it is desirable to have the photocell detector respond to IR radiation.
Advantageously, in operation under high ambient light conditions, where the blades reach only small scanning aperture values, the novel system essentially precludes IR photocell reception and hence, IR evaluation.
However, with lower ambient conditions, as the scan begins to reach larger aperture values, it reduces and subsequently eliminates IR filtering to provide unfiltered recention at these increased exposure values. Since the flash is fired at later rather than early stages of the scan, flash iiS6 firing which assumes greater importance under lowered ambient conditions is thus coincident with the unfiltered reception. Consequently, for this lower ambient condition, the initial, primarily ambient portion of the exposure interval is evaluated under essentially only visible light while during the flash portion of the interval the evaluation employs both visible and infrared scene radiation.
Finally, reference is made to the secondary sweep apertures 39, 40 which are arranged to travel in overlying relation to the IR filter 41 during final scanning of the blades 28, 30 to the terminal position as shown in FIGS . 5 and 5A. During this final stage of such scanning, each of the secondary apertures 39, 40 begin to coincide with the corresponding apertures 36, 37 in overlying relationship to the top and bottom, respectively, of the annular filter 41 (not shown). Thus, some of the scene light is filtered before the central apertures pass out of coincidence over the unfiltered portion 68. This corresponds to the primary apertures 32, 34 defining a maximum primary aperture value. While maintaining this maximum primary aperture, the shutter blades 28, 30 continue to move such that the central secondary apertures 38 pass out of coincidence;
the scene light permitted to pass through to the photocell detector is filtered by the filter 41. When the central apertures 38 pass out of coincidence, the overlapping apertures 39 permit only scene light that has the IR blocked to be evaluated (see FIGS . 5 and 5A) . This blade position occurs only when there is predominantly low ambient light such as during early morning or late evening where the flash effect is negligible, for example, when taking pictures of the Grand Canyon, objects in the scene are too remote to reflect a significant amount of flash intensity. Under such conditions, it is preferred to return to scene evaluation excluding I~ radiation. Consequently, the IR absorption filter 41 is preferred for proper exposure. As explained in the aforementioned references, the blades 28 and 30 can continue to move while maintaining the maximum exposure value due to the fact that the primary aperture blades 32 and 34 are elongated with respect to the entrance aperture 14. Hence, the set of secondar~ sweep apertures 39 progressively coincide in overlying relationship to the top portion of the annular filter 41 as is shown in FIG. 5A while the maximum exposure value remains unchanged. As noted, this portion of an exposure interval only occurs when the ambient scene light is quite low such that it is desirable to reintroduce spectral filtering.
It will be appreciated -that this invention envisions use of a photocell lens having the top halE
portion made so as to block or absorb IR frequencies while the lower half portion is made in a conventional lens fashion which can pass both IR and visible frequencies. The secondary sweep apertures would be, of course, formed so as to achieve the desired filtering control mentioned above during shutter blade scan or strobe. In this regard, for example, under high ambient light conditions an initial pair of cooperating sweep apertures would cooperate over the blocking IR filtered lens half; under relatively low ambient light conditions, another pair of sweep apertures could coincide o~er the non IR-filtered lens half, while the first noted pair of secondary apertures would terminate or close their effective sweep aperture area. Should light conditions dictate that the blades continue to sweep beyond the condition last noted, such as under low or negligible ambient light and wherein the subject is beyond the effective range of the flash, then a third pair of coinciding sweep apertures could pass in overlying relation to the IR filter lens half while the noted second pair of sweep apertures close or terminate their effective sweep aperture area. ~hus, it will be understood, of course, that the foregoing arrangement is designed to control the exposure as did the previously described arrangement.
The light integrating unit provides an evaluation of scene radiation during an evaluation period which, in the illustrated embodiment, occurs essentially simultaneous with at least the initial stages of the exposure interval. Further, since the light integration only continues until a 1.2 volt level is reached, the actual length of the evaluation period is determined by the scene radiation; however, it should be understood that novel arrangements described herein are also applicable to pre-evaluation of scene lighting and to fixed periods of evaluation.
Since certain changes may be made in the above-described system and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the description thereof or shown in the accompanying drawings shall be interpreted as illustrative and not in a llmiting sense.

Claims (18)

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

1. In a photographic apparatus having means for directing image forming light rays from a scene to a photographic film material mounted at a given focal plane, means for evaluating radiation from said scene during an eval-uation period, means for unblocking and blocking passage of said image forming rays to said focal plane, and means responsive to said evaluating means for controlling said unblocking means to define an evaluation period, the improvement wherein said evaluating means includes: means for evaluating scene radiation along a first path for substantially precluding evaluation of selected spectral frequencies and along a second path substantially permitting evaluation of said selected frequencies and additionally inclu-ding means for alternating between said paths during said evaluation period.

2. The apparatus of claim 1 wherein said means for alternating between said paths is responsive to operation of said blocking and unblocking means.

3. The apparatus of claim 1 including means for producing a flash of illumination during evaluation of scene radiation along said second path.

4. The apparatus of claim 1 wherein said means for alternating between said paths includes a blade arrangement having an aperture configuration adapted for blocking one of said paths while opening the other path during movement of said blade arrangement.

5. In a photographic camera apparatus including means for mounting photographic film material at a given focal plane, a light exposure opening for allowing passage of light to the film, means for evaluating scene radiation during an evaluation period, a blade mechanism, means for moun-ting said blade mechanism for displacement between first and second posi-tions, flash means for producing a pulse of illumination directed at the scene for a short portion of the period, said blade mechanism defining primary aperture values enabling a range of changing apertures over said exposure opening when said blade mechanism moves toward said second position and also defining a plurality of discrete secondary aperture values enabling a range of changing aperture values for controlling the amount of scene radiation transmitted to the evaluating means as said blade mechanism moves to the second position, means for displacing said blade mechanism from the first position to the second position and in response to the amount of scene radiation sensed by the evaluating means during the period for retur-ning the blade mechanism to the first position, the improvement comprising:
means in cooperation with said blade mechanism for substantially permitting evaluation of selected spectral frequencies along a first path to the evaluating means during the short portion of the evaluation period while substantially precluding evaluation of said selected frequencies along at least a second path during at least one portion of said period, said means in cooperation with the blade mechanism including means for directing scene radiation along the first path to said evaluating means and having at least one spectral energy filter associated with said directing means to block the evaluation of said selected frequencies along the second path, said filter defining a transmission area which permits evaluation of said selected frequencies along the first path to the evaluating means, said secondary apertures arranged so that during a complete scanning move-ment of the blade mechanism from the first to the second position, a first set of the plurality of said secondary apertures is arranged to be brought into coincidence relative to the second path and the spectral filter for said one portion of the period for preventing evaluation of said selected frequencies along the second path by the evaluation means, a sec-ond set of said secondary apertures is arranged to be brought into coincid-ence over the transmission area during the short portion to allow evalua-tion of said selected frequencies along the first path while the first set is moved out of coincidence to thereby block passage of said selected frequencies along the second path, and a third set of said secondary apertures is arranged to be brought into coincidence relative to the second path and the spectral filter for preventing evaluation of said selected frequencies along the second path to the evaluation means, while the second set is moved out of coincidence to thereby again block evaluation of said selected frequencies along the first path.

6. The camera of claim 5 wherein said means has, in cooperation with said blade mechanism, another spectral filter associated with said trans-mission area, said another filter having a photoresponse different from the photoresponse of said one spectral filter and able to pass the selec-ted frequencies to the evaluating means.

7. In an exposure control system for use in a photographic camera apparatus of the type including means for mounting photographic film material at a given focal plane, a light exposure opening for allowing passage of scene radiation to the film, said system including means for evaluating scene light during an evaluation period, a blade mechanism, means for mounting said blade mechanism for displacement between first and second positions, flash means for producing a pulse of illumination directed at the scene for a short portion of the period, said blade mechanism defining primary aperture values enabling a range of changing apertures over said exposure opening when said blade mechanism moves toward said second position and also defining a plurality of discrete sec-ondary aperture values enabling a range of changing aperture values for controlling the amount of scene radiation transmitted to the evaluating means as said blade mechanism moves to the second position, means for displacing said blade mechanism from the first position to the second position and in response to the amount of scene radiation sensed by the evaluating means during the period for returning the blade mechanism to the first position, the improvement comprising: means in cooperation with said blade mechanism for substantially permitting evaluation of selected frequencies along a first path to the evaluating means during the short por-tion of the evaluation period while substantially precluding evaluation of said selected frequencies along at least a second path during at least one portion of said period, said means in cooperation with the blade mechanism including means for directing scene light radiation along the first path to the evaluating means and having one spectral energy filter associated with said directing means to block the evaluation of said selected frequencies along the second path, said filter defining a transmission area which per-mits evaluation of said selected frequencies along the first path to the evaluating means, said secondary apertures arranged so that during a complete scanning movement of the blade mechanism from the first to the second posi-tion, a first set of the plurality of said secondary apertures is arranged to be brought into coincidence relative to the second path and the spectral filter for said one portion of the period so as to prevent evaluation of said selected frequencies along the second path by the evaluating means, a second set of said secondary apertures is arranged to be brought into coin-cidence over the transmission area during the short portion to allow evalua-tion of said selected frequencies along the first path while the first set is moved out of coincidence to thereby block passage of said selected fre-quencies along the second path, and a third set of said secondary apertures is arranged to be brought into coincidence relative to the second path and the spectral filter for preventing evaluation of said selected frequencies along the second path to the evaluation means, while the second set is moved out of coincidence to thereby again block evaluation of said selected frequencies along the first path.

8. The system of claim 7 wherein said means in cooperation with said blade mechanism has another spectral filter associated with said transmis-sion area, said another filter having a photoresponse different from the photoresponse of said one spectral filter and able to pass the selected frequencies to the evaluating means.

9. A photographic camera apparatus including means for mounting photo-graphic film at a given focal plane, a light exposure opening for allowing passage of scene radiation to the film, means for sensing light from the scene to be photographed including means for providing an output response varying proportionately to the scene light incident thereon, and means spaced from the output response means for directing scene light to the output means, a blade mechanism positioned intermediate the directing means and output means, means for mounting the blade mechanism for displacement between first and second positions to facilitate an exposure interval, flash means respon-sive to said sensing means during the exposure interval for firing a flash at distinct short intervals over a range of times within the exposure inter-val corresponding to a select proportion of a determined exposure value of the sensing means for a short portion of the exposure interval, the blade mechanism defining primary apertures over the exposure opening when the blade mechanism moves from the first position toward the second position and also defining a plurality of discrete sweep secondary apertures enabling a range of corresponding changing sweep aperture values for controlling the amount of scene light sensed by the output means as the blade mechanism moves toward the second position, and means for displacing the blade mechanism from the first position toward the second position and in response to the amount of scene light sensed by the output means for returning the blade mechanism to the first position, the improvement wherein: said directing means inclu-ding a first spectrally filtered portion and a second spectrally filtered portion spaced from the blade mechanism for respectively directing spectrally filtered scene light to the sensing means, said first filtered portion substantially blocking preselected frequencies of the scene light, said second filtered portion substantially permitting transmission of the scene light including said preselected frequencies, and said plurality of discrete sweep apertures formed to substantially unblock passage of scene light passing through the first filtered portion to the sensing means while substan-tially simultaneously enabling blocking of light passing through the second filtered portion to the sensing means at a first time other than the short interval, as the blade mechanism moves toward the second position, said sweep apertures being formed for substantially blocking of light through the first filtered portion to the sensing means while substantially un-blocking the passing of scene light through the second filtered portion to the sensing means during a portion at the short time the flash is fired, said sweep apertures being formed to pass scene light through the first spectral filter while enabling blocking scene light from passing through the second spectral filter during a second time other than the short inter-val.

10. In an exposure control system for use in a photographic camera apparatus of the type including means for mounting photographic film at a given focal plane, a light exposure opening for allowing passage of scene radiation to the film, said system including means for sensing radiation from the scene to be photographed including means for providing an output response varying proportionately to the scene radiation incident thereon, and means spaced from the output response means for directing scene radiation to the output means, a blade mechanism positioned inter-mediate the directing means and output means, means for mounting the blade mechanism for displacement between first and second positions to facilitate an exposure interval, flash means responsive to said sensing means during the exposure interval for firing a flash at distinct short intervals over a range of times within the exposure interval corresponding to a select proportion of a determined exposure value of the sensing means for a short portion of the exposure interval, the blade mechanism pre-cludes scene radiation from reaching the focal plane when in the first position, the blade mechanism defining primary apertures over the exposure opening when the blade mechanism moves from the first position toward the second position and also defining a plurality of discrete sweep secondary apertures enabling a range of corresponding changing sweep aper-ture values for controlling the amount of scene radiation sensed by the output means as the blade mechanism moves toward the second position, and means for displacing the blade mechanism from the first position toward the second position and in response to the amount of scene radiation sensed by the output means for returning the blade mechanism to the first position, the improvement comprising: said directing means including a first spectrally filtered portion and a second spectrally filtered portion spaced from the blade mechanism for respectively directing spectrally fil-tered scene radiation to the sensing means, said first filtered portion subsequently blocking preselected frequencies of the scene radiation, said second filtered portion substantially permitting transmission of the scene radiation including said preselected frequencies, and said plurality of discrete sweep apertures formed to substantially unblock passage of scene radiation passing through the first filtered portion to the sensing means while substantially simultaneously enabling blocking of scene radiation passing through the second filtered portion to the sensing means at a first time other than the range of times in the short interval as the blade mechanism moves toward the second position, said sweep apertures being formed to substantially enable the blocking of scene radiation through the first filtered portion to the sensing means while substantially un-blocking the passing of scene radiation through the second filtered por-tion to the sensing means during a portion at the short time the flash is fired; said sweep apertures being formed to pass scene radiation through the first spectral filter while enabling blocking scene radiation from passing through the second spectral filter during a second time other than the short interval.

11. A method of exposing photographic film comprising the steps of:
initiating a scene light evaluation period by directing image forming scene light rays from a scene to be photographed to photographic film material located at a given focal plane; evaluating selected spectral fre-quencies of the scene illumination along a first path by essentially excluding predetermined frequencies at least during a portion of the evaluation period; evaluating selected spectral frequencies of the scene illumination along at least a second path by including the predetermined frequencies during another portion of the evaluation period; and blocking passage of image forming light rays from the scene to the film in response to a predetermined value of evaluated scene radiation to thereby terminate the evaluation period.

12. The method of exposing photographic material by an exposure control system for use in a photographic camera having means for directing image forming rays from a scene along a given path to the photographic film material mounted in the focal plane of the camera, the system including means for sensing scene radiation during.an exposure interval, a blade mechanism which precludes scene light from reaching the focal plane when in a first position, said blade mechanism defining primary aperture values enabling a range of changing apertures over said exposure opening when said blade mechanism moves toward a second position and also defining a plurality of discrete secondary aperture values enabling a range of changing aperture values for controlling the amount of scene light trans-mitted to said sensing as said blade mechanism moves to the second position, means responsive to said sensing means for controlling the blade mechan-ism to define the exposure interval selected in accordance with an accumulated total of scene radiation sensed by said sensing means, means for producing a short pulse of illumination directed at the scene for a short portion of the exposure interval, a photocell lens which directs scene light radiation onto the sensing means, at least one spectral energy filter associated with said lens to block the selected frequencies through a portion of the photocell lens and another portion defined by the lens which permits passage of the selected frequencies to the sensing means, the improvement comprising the steps of: passing the sweep apertures in scene light transmitting coincidence relative to the spectral filter during movement of the blade mechanism to the second position so as to permit passage of the spectrally filtered scene radiation to the sensing means;
subsequently passing sweep apertures in light transmitting coincidence relative to the other portion defined by the lens to permit passage of scene radiation including the previously spectrally filtered scene radia-tion during the short portion of the interval; and subsequently passing sweep apertures in light transmitting coincidence relative to the spectral filter to again permit passage of the spectrally filtered scene radiation to the sensing means.

13. The method of claim 12 further comprising the step of selectively obstructing the blade mechanism displacement so that the sweep apertures are prevented from being in relative coincidence to the other portion for transmitting radiation when the illuminating means is not going to be pulsed and for permitting unobstructed movement of the blade mechanism when the flash is to be fired.

14. The method of claim 12 further comprising the step of: joining the spectral filter and the other portion along a given extent which is gener-ally parallel to a path traveled by the passing sweep apertures.

15. In a photographic apparatus having means for directing image forming light rays from a scene along a given path to a photographic film material mounted at a given focal plane, means for evaluating radiation from said scene during an evaluation period, means for unblocking and blocking said path, and means responsive to said evaluation means for controlling said unblocking means to define an exposure interval, the improvement wherein said evaluating means includes: means responsive to operation of said unblocking and blocking means for automatically substantially precluding evaluation of selected spectral frequencies during at least one portion of the operation of said unblocking and blocking means while substantially permitting evaluation of said selected frequencies during at least another portion of the operation of said unblocking and blocking means.

16. The camera of claim 15 including means for producing a flash of illumination during said other portion of said period.

17. In a photographic camera apparatus including means for mounting photographic film material at a given focal plane; a light exposure open-ing for allowing passage of light to the film; detecting means for evalua-ting scene light; a blade mechanism mounted for displacement between a first and second position; said blade mechanism precluding passage of scene light through said exposure opening when in said first position and defining changing primary aperture values over said exposure opening and changing secondary aperture values over said detecting means as said blade mechanism moves toward said second position; and drive means actuatable for initially displacing said blade mechanism from said first position toward said second position and, in response to the amount of scene light detec-ted by said detecting means, for returning said blade mechanism to said first position, the improvement comprising: filtering means responsive to displacement of said blade mechanism for automatically precluding trans-mission of light of selected frequencies to said detecting means during at least one portion of said displacement of said blade mechanism toward said second position and for transmitting said selected frequencies to said detecting means during another portion of said displacement.

18. In an exposure control system for photographic apparatus of the type including means for positioning photographic film material at a given focal plane, a light exposure opening allowing passage of scene light to the film; said system including scene light detecting means for detecting scene light transmitted to said focal plane; a blade mechanism including a shutter blade having a spaced apart primary and secondary aperture, said primary aperture arranged to enable changing aperture sizes over said exposure opening and said secondary aperture arranged to enable a range of changing aperture sizes over said light detecting means during movement of said blade from a first to a second position; means for mounting said blade element for displacement between said first and second positions;
and selectively actuatable drive means for displacing said blade between said first and second positions, the improvement wherein said detecting means comprises: means responsive to operation of said unblocking means including filtering means responsive to displacement of said blade mechanism for automatically precluding transmission of light of selected frequencies to said detecting means during at least one portion of said displacement of said blade mechanism toward said second position and for transmitting said selected frequencies to said detecting means during another portion of said displacement.