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Add magnification and blowup & reduction sections

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Matt McWilliams 2022-07-26 14:27:58 -04:00
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NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md
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@ -64,14 +64,46 @@ March 1983
An optical printer is a device for photographing the frames of one film so as to make another film. An optical printer is a device for photographing the frames of one film so as to make another film.
**![Graphic depicting labelled components camera, bellows, lens, gate and lamp](#)**
It consists essentially of a camera (C) connected by a bellows (B) to a lens (L) aimed at a film in a gate (G) illuminated from behind by a lamp (I). It consists essentially of a camera (C) connected by a bellows (B) to a lens (L) aimed at a film in a gate (G) illuminated from behind by a lamp (I).
The camera and gate each have motorized intermittant film movements so that any frame of the "original" film can be conveniently photographed onto any frame of the "print" film. The camera and gate each have motorized intermittent film movements so that any frame of the "original" film can be conveniently photographed onto any frame of the "print" film.
The camera can be an ordinary cine camera, less its lens, and the gate can be an ordinary cine projector, less its lens. The camera can be an ordinary cine camera, less its lens, and the gate can be an ordinary cine projector, less its lens.
Ideally they have identical syatems of film registration, as if one were the lens' image of the other. Ideally they have identical systems of film registration, as if one were the lens' image of the other.
The lens can be any bellows mountable lens. The lens can be any bellows mountable lens.
Ideally it is specially corrected for the small and nearly equal sizes of this object and image. Ideally it is specially corrected for the small and nearly equal sizes of this object and image.
The camera and the lens can elide independently to and fro the film gate. The camera and the lens can slide independently to and fro the film gate.
Thie adjusted the magnification and the focus of the photography. This adjusted the magnification and the focus of the photography.
## Magnification
If the lens is (nominally) midway between the films when one is focused on the other, then the magnification is 1.
At `M = 1` (also called 1:1) the whole of the original frame is photographed at a size which fills the whole of the print frame.
**!["M = 1" Graphic depicting two frames with a lens at their midpoint with a lightbulb illuminating from the right](#)**
If the lens is moved closer to the gate, then the camera must be moved back, farther from the gate, to keep the one film focused on the other.
Then the magnification is greater than 1.
At `M > 1` a part of the original frame is photographed at a size which fills the whole of the print frame.
**!["M = 3" Graphic depicting two frames with a lens closer to the right projection source image with the lamp demonstrating an enlargement](#)**
If, starting from the 1:1 setup, the lens is moved farther from the gate, then the camera must also be moved back, farther from the gate, to keep the one film focused on the other.
Then the magnification is loser than 1.
At `M < 1` the whole of the original frame is photographed at a size which does not fill the whole of the print frame.
The remainder of the print frame is filled with a photograph of the gate as it surrounds the original frame (ideally perfectly black).
**!["M = 1/3" Graphic depicting two frames with a lens closer to the left camera image demonstrating a reduction](#)**
For each position of the lens there is exactly one correct (focused) position for the camera.
But for each position of the camera (except the 1:1 position) there are two correct positions for the lens. One gives `M > 1`, the other `M < 1`.
## BLOWUP & REDUCTION
The printer gate may hold 8mm film and the printer camera 16mm, or vice versa.
With a `M = 2` setup an 8mm original frame is photographed onto a whole 16mm frame.
With an `M = 1/2` setup a whole 16mm original frame is photographed onto an 8mm frame.
Conversion between any two film gauges is possible this way, provided the frames have the sane proportions, as 8mm, super 8mm, 16mm, and some 35mm do.