GB2078986A

GB2078986A - Method and apparatus for controlling exposure time for photosensitive materials in consideration of reciprocity law failure

Info

Publication number: GB2078986A
Application number: GB8119514A
Authority: GB
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1980-06-27
Filing date: 1981-06-24
Publication date: 1982-01-13
Also published as: FR2485757B1; GB2078986B; IT1171341B; DE3124693A1; ES8300206A1; IT8148784A0; DE3124693C2; FR2485757A1; DK279981A; ES503365A0

Abstract

In a process camera in which variation in required exposure time caused by variation of the photographic conditions such as reproduction scale, diaphragm opening size, and highlight density value, is corrected according to an operational equation when the reciprocity law of the photosensitive material holds good. The present method corrects the reciprocity law failure of the photosensitive material by inserting a correction factor or factors predetermined in the operational equation, thereby determining a proper exposure time. <IMAGE>

Description

SPECIFICATION Method and apparatus for controlling exposure time for photosensitive materials in consideration of reciprocity law failure This invention relates to a method and apparatus for controlling an exposure time in consideration of the reciprocity law failure of a photosensitive material, for use in a picture reproducing machine such as a process camera, and the like.

In a conventional automatic process camera, distances between a picture holder and a lens holder and between a photosensitive film holder and the lens holder are automatically determined depending on a reproduction scale, and then a proper exposure time for the photographying conditions is automatically determined depending on the reproduction scale, diaphragm opening size, and the density of the essential part of an original picture in order to photograph the original picture properly and automatically.

The obtained exposure time is only correct as long as the reciprocity law for the photosensitive film used holds goods, but under photographing conditions for which the reciprocity law for the photosensitive film does not hold good, the exposure time is in practice incorrect.

In order to correct the reciprocity law failure and obtain a proper exposure time, the photosensitive characteristics of the photosensitive material should be known as well as the experimental knowledge of the operator. Hence, in practice, under the photographing conditions where reciprocity law failure occurs, the exposure time is automatically obtained as if the reciprocity law holds good, and then a correction time determined by the operator based on his experience, is added to or subtracted from the obtained exposure time. In this instance, therefore, in fact, the automatic exposure control is inadequate.

The reason why the experimental knowledge of the operator is required for correcting for the reciprocity law failure, is as follows. The photosensitive characteristics depend on the photosensitive materials being used, and the exposure time varies depending on the distance between the picture holder and the lens holder and between the photosensitive film holder and the lens holder at a certain reproduction scale, the diaphragm opening size, and the density of the original picture, which synergistically affect one another.

Further, it is experimentally confirmed that the exposure time is varied when the lens is changed for one of a different focal length in order to vary the reproduction scale. Accordingly, since these factors synergistically affect one another, the correction time cannot be obtained by a conventional method.

It is an object of the present invention to provide a method for controlling exposure time in consideration of the reciprocity law failure of a photosensitive material, for use in a picture reproducing machine such as a process camera, free from the aforementioned defects, which is capable of performing an accurate, automatic and quick control of exposure time, and reproducing a consistent picture image regardless of the photographing conditions.

According to one aspect of the present invention there is provided a method for controlling an exposure time in consideration of the reciprocity law failure of a photosensitive material, for use in a picture reproducing machine wherein the exposure time variation caused by varying the photographing conditions is corrected according to an operational equation when the reciprocity law of the photosensitive material holds good, characterised in that a correction factor predetermined for correcting the reciprocity law failure of the photosensitive material is inserted in the operational equation, thereby determining a proper exposure time for which the reciprocity law failure is corrected.

The invention in its other aspect comprises apparatus constructed to carry out the above method.

In order that the present invention may be better understood, preferred embodiments thereof will be described with reference to the accompanying drawings, in which: Figure 1 is an elevational view of an upright process camera which performs a method according to the present invention; Figure 2 is a rig ht side view of Figure 1; Figure 3 is a block diagram of a control system of the process camera shown in Figures 1 and 2; Figure 4 is a graph showning one example of the reciprocity law failure of a photosensitive material used in the present method; Figure 5 is an enlarged view of Figure 4; Figure 6 is a block diagram of the first embodiment of an exposure time determination system which calculates the proper exposure time in consideration of the reciprocity law failure of a photosensitive material according to the present invention;; Figure 7 is a block diagram of the second embodiment of the exposure time determination system according to the present invention; Figure 8 is a block diagram of the third embodiment of the exposure time determination system according to the present invention; and Figure 9 shows one embodiment of an analog exposure time determination system according to the present invention.

Description ofpreferred embodiments Referring now to the drawings there is shown in Figures 1 and 2 an automatic upright process camera which carries out a method according to the present invention, comprising an original picture holder 1 made of a transparent or light display plate on which an original picture is mounted, a lens holder 2, a film holder 3 on which either film support frame 4 on which a photosensitive material or fiim is mounted, or focusing glass screen 5 is located, the frame 4 and screen 5 being pivotally mounted via support members 11 or 12 so that they can be rotated away from the holder 3 to respective sides thereof. The three holders 1, 2 and 3 are aligned on a vertical axis.An operational board 6 is disposed to the front of the film holder 3, pairs of lights 7 are mounted on the original picture holder 1 via brackets for reflected light photography of the original picture, and a light 7' is mounted under the original picture holder 1 for transmitted light photography of the original picture.

The picture holder 1 and the lens holder 2 are movable vertically towards or away from the fixed film holder 3. The positions of the three holders 1, 2 and 3 are automatically settled depending on a reproduction scale input to the operational board 6.

A plurality of focusing lenses 8a, 8b and 8c having different focal lengths are interchangeably mounted on the lens holder 2, and a shutter 9 for controlling the main exposure time and a diaphragm adjuster 10 which adjusts the diaphragm of each focusing lens. The lens holder 2 is provided with a flash lamp (not shown) for a flash exposure.

The film support frame 4 is provided with an air suction pipe 13 in the center of its upper surface. The suction pipe 13 is connected to suction means (not shown) such as a vacuum pump. The photosensitive film is tightly retained by and onto the film support frame 4 by sucking air through the suction pipe 13.

The automatic process camera shown in Figures 1 and 2 is operated by a key board, switches, buttons, and the like, provided on the operational board 6, as hereinafter described in detail.

In Figure 3 is shown a control system for the process camera of Figures 1 and 2. The operational board 6 is connected to a central processing unit 15, hereinafter referred to as CPU for short, via an interface 14. The CPU 15 automatically controls the process camera according to the data input from the operational board 6.

Drive signals are output from the CPU 15 to a picture holder controller 16 and a lens holder controller 17 via the interface 14, and then the picture holder controller 16 and the lens holder controller 17 drive the picture holder 1 and the lens holder 2. The positions of the picture holder 1 and the lens holder 2 are detected by first and second position detectors 18 and 19. The position data detected by the position detectors 18 and 19 is fed to the CPU 15 through the interface 14. Then, the CPU 15 calculates the required positions of the picture holder 1 and the lens holder 2, from the position data obtained and the desired reproduction scale input from the operational board 6, and controls the picture holder 1 and the lens holder 2 to move them to their required positions.

The lights 7 and 7', the shutter 9, and the flash lamp 22 in the lens holder 2 are controlled respectively by a light controller 20, a main exposure controller 21 and a flash exposure controller 23 according to control signals fed thereto from the CPU 15 via the interface 14.

In a conventional main exposure time control method, an exposure time Ta for which the reciprocity law holds good, is calculated by the CPU 15 according to the following equation (1), wherein Mi Fi and Di mean a desired reproduction scale, a desired diaphragm opening size and a highlight density value of the essential part of the original picture, respectively, which are fed from the operational board 6, and wherein Fo, Do and To mean a reference diaphragm opening size, a reference highlight density value and a reference proper exposure time of a reference picture at a reproduction scale of unity, which are predetermined.

However, this equation is not always satisfied under all photographying conditions because of reciprocity law failure which depends on the photosensitive material and exhibits different characteristics for each photosensitive material.

In Figures 4 and 5 is shown a graph of one example of experimental data of reciprocity law failure of a photosensitive material named "FUJILITHORTHO VO-100", wherein is shown the relation between the reproduction scale Mi and the proper exposure time Ti which are obtained by using the same copy under the following photographing conditions: Di=Do; fixed diaphragm opening number F11; Fi=Fo; and screen number 150 lines/inch of a contact screen used.

Curve A shown by a solid line is a theoretical characteristics line obtained according to the equation (1) under the above photographing conditions. On the other hand, when the proper exposure time for the reproduction scale Mi is Ti, a theoretical proper exposure time T2 Of the reproduction scale M2 is obtained disregarding other factors according to the following equation.

Accordingly, since the reproduction scale is unity, and both terms (Fi/Fo)2 and 10Di-D0 are unity under the above described conditions, the theoretical characteristics curve A is expressed as follows.

A characteristics curve B shown by a broken line is obtained by using a lens having a focal length of 150 mm. The reciprocity law failure occurs exponentially as the reproduction scale is increased away from 100%.

Characteristics curve C shown by a chain-dotted line is obtained by using another lens having a focal length of 210 mm. Theoretically, the curve C should be the same as the curve B, but it is not. This means that the characteristics curve for reciprocity law failure is varied by changing a lens of one focal length for a lens of different focal length.

Therefore, it can be seen from these experiences that in order to obtain a proper exposure time in consideration of the reciprocity law failure, variable factors for correcting the reciprocity law failure are determined and are inserted in the equations (1) and (2) so that the equations including the correction factors may represent well the curves such as B and C having the reciprocity law failure characteristics.

In this embodiment, in order two correct the reciprocity law failure of the magnification variation, a correction factor P is inserted in the formula (2), thereby obtaining the following empirical formual (3), wherein Tm means a proper exposure time of which the reciprocity law failure due to the magnification variation is corrected.

Then according to the formula (3) the correction factors P of the three characteristics curves A, B and C are calculated, for example, by substituting the values picked up from the curves A, B and C, to obtain P=1.00 for the curve A; P=1.14 for the curve B; and P=1.06 for the curve C, the thus obtained factors well satisfying the formula (3).

Next, the other correction factors Q and R for correcting the reciprocity law failures caused by the diaphragm opening size variation and the highlight density value variation of the picture are obtained in the same manner as described above.

When the reciprocity law holds good with respect to the diaphragm opening size variation, the theoretical exposure time Ta is expressed in the following equation (4) which is obtained by substituting Mi=1 and Di=Do into the equation (1).

The correction factor Q for the reciprocity law failure due to the diaphragm opening size variation is obtained according to the following empirical formula (5) wherein Tf means a proper exposure time of which the reciprocity law failure due to the diaphragm opening size variation is corrected, in the same manner as the correction factor P.

When the reciprocity law holds good with respect to the highlight density value variation, the theoretical exposure time Ta is represented in the following formula (6) which is obtained by substituting Mi=1 and Fi=Fo into the formula (1).

Ta = 10Di-D0.To (6) The correction factor R for the reciprocity law failure due to the density value variation is obtained according to the following empitical formula (7) wherein Td means a proper exposure time of which the reciprocity law failure due to the highlight density value variation is corrected, in the same manner as above.

Td =1O'D'-DO'R.To (7) Hence, when the reproduction scale Mi, the diaphragm opening size Fi and the highlight density value Di vary mutually and affect synergistically one another, a proper exposure time Ti of which the reciprocity law failure is corrected, is obtained according to the following formula (8).

In this case, the correction factors P, 0 and R are empirically determined according to the formulae (3), (5) and (7) by using the characteristics curve for each photosensitive material, such as the one shown in Figure 4 or 5, in the same manner as described above. That is, the correction factors P, 0 and R are obtained depending on the photosensitive material.

Since the correction factor P varies for lenses having different focal lengths it is determined for every interchangeable lens in advance.

When the correction factors P, 0 and R of the photosensitive material are determined according to the formula (8), a serial number Ai is attached to the photosensitive material. The serial number Ai is input to the operational board 6. Another serial number Bi is also attached to the interchangeable lens 8a, 8b or 8c, and it is input to the operational board 6. The correction factors Pi, Oi and Ri predetermined as described above, corresponding to the serial numbers Ai and Bi, are stored in a memory 25.

The photographing condition data such as the reproduction scale Mi, the diaphragm opening size Fi, the highlight density value Di, the photosensitive material serial number Ai, and the lens serial number Bi are fed from the operational board 6 to a register 24 via the interface 14 and they are stored in the register 24.

Then, the serial numbers Ai and Bi of the photosensitive material and the lens are sent from the register 24 to the memory 25, and the corresponding correction factors Pi, Qi and Ri are read out of the memory 25 by using the serial numbers Ai and Bi. Then, the read-out correction factors Pi, Qi and Ri are fed to the CPU 15 via the interface 14. At the same time, the reproduction scale Mi, the diaphragm opening size Fi and the highlight density value Di are also input to the CPU 15 via the interface 14. Then, the CPU 15 calculates a proper exposure time Ti from the input data Mi, Fi and Di, and the correction factors Pi, Qi and Ri according to the formula (8).

In Figure 6 there is shown the first embodiment of an exposure time determination system which calculates a proper exposure time Ti according to the formula (8) by means of the CPU 15.

The correction factors Pi, Qi and Ri are stored in memory units 25P, 250 and 25R having independent addresses of the memory 25. The correction factor Pi relative to the reproduction scale Mi is read out of the memory unit 25P by addressing by means of the serial numbers Ai and Bi. The correction factors Oi and Ri in relation with the diaphragm opening size Fi and the highlight density value Di are read out of the memory units 25Q and 25R respectively by addressing by means of the serial number Ai.

The correction factors Pi, Qi and Ri read out of the memory units 25P, 250 and 25R are sent to calculation means 26, 27 and 28 which calculate the reproduction scale term (1 + Mi/2)2P, the diaphragm opening size term (Fi/Fo)2Q, and the highlight density value term 10(Di-D0)R of the formula (8), respectively, to obtain output values m, f and d. Thus the obtained output values m, f and d are multiplied together in a calculation means 29 to obtain a total factor S by which the reference proper exposure time To is changed to the proper exposure time To for photographing, as below. That is, the total factor S is multiplied to the reference exposure time To in a calculation means 30 to obtain the proper exposure time Ti for correcting the reciprocity law failure.Then, the main exposure controller 21 is controlled by the proper exposure time Ti obtained so that the shutter 9 may properly be operated.

In the embodiment shown in Figure 6, since the proper exposure time Ti is calculated in consideration of the reciprocity law failure, it is impossible to obtain the proper exposure time Ti by correcting the theoretical exposure time Ta which is obtained according to the equation (1) as if the reciprocity law holds good, by multiplying the variance caused by the reciprocity law failure thereto.

In Figure 7 there is shown the second embodiment of the exposure time determination system. In this embodiment, the theoretical exposure time Ta is calculated according to the formula (1) as if the reciprocity law holds good, and then correction coefficients caused by three reciprocity law failure are obtained and are multiplied to the theoretical exposure time Ta, thereby obtaining the proper exposure time Ti, as hereinafter described in detail.

Prior to the explanation of the Figure 7, the correction coefficients of the reproduction scale term, the diaphragm opening size term, and the highlight density value term, which are caused by the reciprocity law failure, are obtained by using the formulae (1) and (8).

When the values of the three terms are replaced by mO, f0 and do, as follows,

10Di Do = do the proper exposure time Ti is obtained by multiplying the values mO, f0 and do of the three terms by the correction coefficients a, ss and y of the three terms, caused by reciprocity law failure, in the following formula (9).

Ti = amO.ssf0.yd0.To (9) On comparing the formula (8) with the formula (9), the correction coefficients a, ss andy are obtained as follows.

m0P = αm0 - > α = m0P-1 ..... (10) foo=pr, ss=f0Q-1 .....(11) doR = ydO > y = d0Rl (12) In this embodiment, instead of the correction factors P, 0 and R of the first embodiment, index numbers (P-l), (Q-1) and (R-1) for obtaining the correction coefficients a, ss andy by using the formulae (10), (11) and (12) are stored in the memory units 25P, 250 and 25R.

In a block 31 shown in Figure 7 by a two-dotted line, calculation means 32 - 35 being included, the calculation means 32, 33 and 34 calculate the values mO, f0 and do respectively, and the calculation means 35 multiplies the reference exposure time To by the obtained values mO, f0 and do sent from the calulation means 32 - 34, thereby obtaining the theoretical exposure time Ta which is to be sent to calculation means 40.

Meanwhile, the values mO, f0 and do are fed from the calculation means 32,33 and 34 to calculation means 36,37 and 38, respectively, and the index numbers (Pi-1), (Qi-1) and (Ri-1) are also sent from the memory units 25P, 25Q, and 25R to the calculation means 36, 37 and 38, respectively. In the calculation means 36, 37 and 38 correction coefficients ai, ssi and yi are calculated according to the formulae (10), (11) and (12).

Thus the obtained correction coefficients ai, ssi and yi are multiplied together in calculation means 39 to obtain a total correction coefficient 5i which is sent to the calculation means 40. Then, the theoretical exposure time Ta and the total correction coefficient 5i are multiplied together to obtain the proper exposure time Ti of which the reciprocity law failure is corrected. Then, the main exposure controller 21 is controlled by the proper exposure time Ti so that the shutter 9 may properly be opened or closed.

In Figure 8 there is shown the third embodiment of the exposure time determination system having almost the same construction as the one of Figure 7, except that the calculation means 36 - 38 are omitted, and that the correction coefficients ai, ssi and yi obtained according to the formulae (10), (11) and (12) are stored in the memory units 25P, 250 and 25R.

In this embodiment, the correction coefficient ai is read out of the memory unit 25P by addressing by means of the reproduction scale Mi and the serial numbers Ai and Bi. The correction coefficient ssi is read out of the memory unit 25Q by addressing by means of the diaphragm opening size Fi and the serial number Ai, and the correction coefficient γi is read out of the memory unit 25R by addressing by means of the highlight density value Di and the serial number Ai.

The correction coefficients ai, ssi and yi read out are sent to the calculation means 39 and the total correction coefficient 5i is calculated therein in the same manner as the second embodiment shown in Figure 7. The other steps are the same as those of the second embodiment and thus need not be further described.

In this case, even when the theoretical exposure time Ta is obtained by another means different from the one included in the block 31, the correction of the reciprocity law failure can be carried out.

Further, in a picture reproducing apparatus in which the photosensitive material and the focusing lens are not interchangeable, the correction coefficients a, ss and y correspond to the reproduction scale Mi, the diaphragm opening size Fi and the highlight density value Di. Hence, the memory units 25P, 25Q and 25R of a fixed type memory having a small capacity can be employed.

In the embodiments shown in Figures 6 - 8, the calculation means may be digital or analog calculation circuits. When the calculation means are analog calculation circuits, the data output from the memory 25 must be converted from the digital data into the analog data in digital-analog converters.

In the analog calculation, the correction factors P, Q and R, the index numbers (P-1), (Q-1) and (R-1), and the correction coefficients a, ss andy may be set by using analog data settlers. For example, analog valtages are set by potensiometers in order to set the factor P, Q and R corresponding to the serial numbers of the photosensitive materials on the basis of a table including the correction factors P, Q and R of the photosensitive materials, without using the memory units.

In Figure 9 there is shown one embodiment of an analog exposure time determination system which performs a method like the one which is carried out by the system of Figure 7.

In this embodiment, the reproduction scale Mi, the diaphragm opening size Fi and the highlight density value Di set in the analog values are input to a reproduction scale term calculation circuit 41, a diaphragm opening size term calculation circuit 42 and a highlight density value term calculation circuit 43, which output the values mO, f0 and do, respectively. Then, the calculation values mO, f0 and do are fed to logarithmic converters 44, 45 and 46, respectively, wherein the values mO, f0 and do are logarithmically converted.

Then, the logarithmically converted values log mO, log f0 and log do are sent to respective potentiometers 48, 49 and 50 in which the divisional ratios corresponding to the index numbers (P-1), (Q-1) and (R-1) are set respectively, an adder 47 comprising an operational amplifier and resisters shown by a one-dotted line, and are converted therein into logarithmic values log a, log ss and log y of the correction coefficients a, ss andy, such as according to the following equations.

log a = (P-1)log mO log ss = (Q-1)log fO log y = (R-1)log do A logarithmic value log To of the reference exposure time To is fed from a logarithmic value settler 51 to the adder 47. The logarithmic values log a, log p, log y and log To are added in the operational amplifier of the adder 47 to output a logarithmic value log Ti of the proper exposure time, of which the reciprocity law failure is corrected. Then, the logarithmic value log Ti is converted into the proper exposure time Ti in an antilogarithmic converter 52. Then, the signal corresponding to the proper exposure time Ti is sent to a main exposure controller 21', and it controls the main exposure controller 21' so that the shutter 9 may properly be opened or closed.

When the index number (P-1), (Q-1) or (R-1) is negative value, its absolute value is set to the potentiometer 48,49 or 50 as the divisional ratio, and the output signal of the potensiometer 48,49 or 50 is fed to a subtraction terminal 53 of the operational amplifier of the adder 47.

According to the present invention, the proper exposure time Tm with respect to the magnification variation can be obtained according to the following empirical formula (13), instead of the formula (3), wherein P' means a correction factor for correcting the reciprocity law failure due to the magnification.

The proper exposure time Tf or Td with respect to the diaphragm opening size Fi or the highlight density value Di may also be obtained in the similar manner to the above method relative to the formula (13).

Although the present invention has been described with reference to preferred embodiments thereof in connection with the accompanying drawings, however, various changes and modifications thereof can be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. A method for controlling an exposure time in consideration of the reciprocity law failure of a photosensitive material, for use in a picture reproducing machine wherein the exposure time variation caused by varying the photographing conditions is corrected according to an operational equation when the reciprocity law of the photosensitive material holds good, is characterised in that a correlation factor predetermined for correcting the reciprocity law failure of the photosensitive material is inserted in the operational equation, thereby determining a proper exposure time for which the reciprocity law failure is corrected.

2. A method as defined in claim 1, wherein the operational equation includes a reproduction scale term, a diaphragm opening size term and a density value term.

3. A method as defined in claim 2, wherein a correction factor n1 for correcting the reciprocity law failure due to a reproduction scale variation is inserted in the operational equation so as to raise the reproduction scale term to the n1th power.

4. A method as defined in claim 2, wherein a correction factor n2 for correcting the reciprocity law failure due to a diaphragm opening size variation is inserted in the operational equation so as to raise the diaphragm opening size term to the n2th power.

5. A method as defined in claim 2, wherein a correction factor n3 for correcting the reciprocity law failure due to a density value variation is inserted in the operational equation so as to raise the density value term to the n3th power.

6. A method as defined in claim 2, wherein the correction factors n1 and n2 are inserted in the operational equation so as to raise the reproduction scale and the diaphragm opening size terms to the n1th and the n2th powers respectively.

7. A method as defined in claim 2, wherein the correction factors n2 and n3 are inserted in the operational equation so as to raise the diaphragm opening size and the density value terms to the n2th and the n3th powers respectively.

8. A method as defined in claim 2, wherein the correction factors n3 and n, are inserted in the operational equation so as to raise the density value and the reproduction scale terms to the n3th and the n1th powers respectively.

9. A method as defined in claim 2, wherein the correction factors n1, n2 and n3 are inserted in the operational equation so as to raise the reproduction scale, the diaphragm opening size and the density value terms to the n1th, n2th and n3th powers respectively.

10. A method as defined in claims 1,2,3,4,5,6,7,8, or 9, wherein the correction factors for each photosensitive material are stored in a memory.

11. A method as defined in claims 1,2,3,6,8,9 or 10, wherein the correction factors obtained depending on each photosensitive material and each interchangeable focusing lens are stored in the memory.

12. A method as defined in claims 1, 2,3,4, 5,6,7, 8 or 9, wherein correction coefficients to be multiplied to the theoretical value obtained according to the operational equation, are obtained on the basis of the correction factors.

13. Apparatus constructed to carry out the method of any preceding claim.

14. A method for controlling exposure time substantially as hereinbefore described with reference to the accompanying drawings.

15. A system for controlling exposure time substantially as hereinbefore described with reference to Figures 3 and 6 or Figure 7 or Figure 8 or Figure 9.