JPS6118173B2 - - Google Patents

Description

[Detailed description of the invention] In photography, if the appropriate exposure time is T ₁ when the imaging magnification is m ₁ , then the appropriate exposure time T ₂ when the imaging magnification is changed to m ₂ can be calculated theoretically from the following formula. You can ask for it.

T ₂ = (1+m ₂ ) ² / (1+m ₁ ) ²・T ₁ ………(1
) In plate-making cameras, actual size photography is often used as a standard, so if the appropriate exposure time at this time is T ₀ , then from equation (1), the appropriate exposure time T at any magnification m can be calculated as follows: It can be derived as follows.

T=(1+m/2) ²・T ₀ ......(2) However, when actually using a prepress camera, the value of T obtained from equation (2) is not appropriate for the following reasons. It is difficult to obtain accurate shooting results.

In other words, the amount of exposure to a photographic photosensitive material can be expressed as the product IT of the intensity I of light irradiated onto the photosensitive material and its irradiation time T, and for an ideal photosensitive material where the reciprocity law holds, IT is constant. If so, I
Alternatively, the same exposure result can be obtained regardless of the value of T.

However, in actual photosensitive materials, the reciprocity law does not hold if I changes over a relatively wide range. This phenomenon is called reciprocity failure, and differs depending on the photosensitive material.

Furthermore, in actual cameras, in addition to the original imaging light, some flare light reaches the photosensitive material, which also impedes proper exposure.

The following experimental formula is available as an alternative to formula (2) for determining T after correcting the reciprocity law failure and flare described above.

T=(1+m/2) ^2P ·T ₀ (3) (However, P...correction coefficient) Alternatively, it has been confirmed through experiments that the following equation may be used as an approximate equation.

T={2+(m-1)α}/4・T ₀ ………(4) (However, α…correction coefficient) The attached Figures 1 and 2 show the gray screen on commercially available plate-making film. When using 150L, the curve obtained by experimentally determining the P value of equation (3) under each photographing condition for each photographing magnification is compared with the theoretical curve of an ideal photosensitive material with P = 1.0. It shows.

However, in conventional photography, corrections for reciprocity failure and flare mostly depend on the photographer's experience, so when the photographer changes, etc.
In addition, when proper exposure cannot be obtained, and when a plate-making camera is used for general purposes, there are many types of photosensitive materials used, so exposure management to correct reciprocity law failure for each photosensitive material is extremely troublesome. be.

The present invention relates to an exposure control method for a plate-making camera, which eliminates the above-mentioned drawbacks and makes it possible to easily obtain the appropriate exposure even if the photographer changes or the photosensitive material changes. This will be explained in detail based on the drawings.

3 and 4 show a vertical plate-making camera for carrying out the method of the present invention, in which 1 is an original picture rack;
2 is a lens rack, 3 is a photographic rack, 4 is a photographic film frame, 5 is a focusing glass frame, 6 is an operation panel installed in the front of the photographic rack 3, and 7 is a reflective illumination lamp.

The original picture rack 1 and the lens rack 2 are raised and lowered by operating a magnification setting button on the operation panel 6, and are automatically focused at a predetermined magnification. Lenses 8, 9, and 10 are attached to the lens rack 2.

As shown by the arrow in FIG. 3, the film frame 4 on the photographing rack 3 can be moved to the right, and the focusing glass frame 5 can be swung between the photographing rack 3 and its upper left. can be done.

Reference numerals 11 and 12 are receiving frames for the film frame 4 and focusing glass frame 5, respectively.

A suction port 3 is protruded from the center of the upper surface of the film frame 4, and this suction port 13 is connected to a suction device (not shown), so that the photographic film (not shown) can be
It is held by suction on the film frame 4.

The above is the same as a known plate-making camera, but this plate-making camera has buttons on the operation panel 6 that allow you to
A large number of P values corresponding to various photosensitive materials and other conditions are stored via the interface 14,
Additionally, a central processing unit (hereinafter referred to as CPU) 15 is provided which can output a required P value as required.

To photograph the original picture on the original picture rack 1 onto the film in the film frame 4 using this plate-making camera,
A large number of required P values are stored in the CPU 15 in advance.

When photographing, select and output the P value according to the photographing conditions by operating the buttons on the operation panel 6.
Next, when the photographing magnification is set, the original picture rack 1 and the lens rack 2 move to predetermined positions as described above, and the shutter (not shown) is set to the appropriate exposure time T corrected with the P value. .

Next, when an exposure operation is performed using a button on the operation panel 6, the illumination lamp 7 is turned on, and after the shutter is opened and closed to perform proper exposure, the illumination lamp 7 is turned off.

As described above, according to the present invention, once a large number of required P values are stored in the CPU 15,
The photographer does not need any experience or skill, and can simply and easily perform appropriate exposure according to the various types of photosensitive materials used by operating buttons.

In addition, when performing exposure using the flash lamp built into the lens rack 2, in order to obtain constant illuminance on the film surface, conventional methods have been used to
It required special equipment to adjust the voltage, but
In the present invention, the output of the CPU 15 can be used to automatically adjust.

In addition, in the above explanation, the P value in the above equation (3) was used to correct the exposure, but almost the same effect can be obtained by using the α value in the equation (4) instead. I can do it.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between imaging magnification and exposure ratio under various imaging conditions when the same photosensitive material is used at low imaging magnification, and Figure 2 is a diagram showing the same at high imaging magnification. 3 is a front view of a vertical plate-making camera for carrying out the method of the present invention, FIG. 4 is a side view thereof, and FIG. 5 is a block diagram showing the same operation. 1...Original picture rack, 2...Lens rack, 3...Photography rack, 4...
Film frame, 5... Focusing glass frame, 6... Operation panel,
7...Lighting lamp, 8,9,10...Lens, 11,12
...Receptacle frame, 13...Suction port, 14...Interface, 15...CPU.

Claims (1)

[Claims] 1. An original picture rack, a lens rack, and a photographing rack are arranged in this order, and the original picture on the original picture rack is projected onto the photosensitive material on the photographing rack at variable magnification depending on the relative distance of each rack. When changing the magnification, based on the appropriate exposure time T ₀ determined in advance for the original size magnification, the relational expression for calculating the appropriate exposure time T of the projected image that has been changed by m times the original size magnification is expressed as T=(1+m/ 2) In a plate-making camera with ²・T ₀ , the appropriate exposure time T=(1+m/2) ^2P・T ₀ , including the exposure correction coefficient P for the reciprocity law failure of various photosensitive materials and the camera's unique flare. The value of P in the equation for calculating is experimentally determined in advance and stored electronically in the central processing unit, and before the start of photography, the exposure correction coefficient P corresponding to the photosensitive material used and the photography conditions is selected, An exposure time control method for a prepress camera, characterized in that the exposure time is automatically corrected and set using a selected correction coefficient by a shooting magnification setting operation.