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Add Aimframe section

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Matt McWilliams 2022-07-26 15:12:48 -04:00
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NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md
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@ -232,3 +232,43 @@ It helps, after they are set, to gently tap the lens, so it finds a stable posit
The lateral movements of the lens, the to-fro movements of the lens and camera, and a tilting of the camera (if necessary) allow the optical printer to be set for exact 1:1 reproduction.
Then the printed image is the same size and in the same position as the original image.
If the printer lacks a tilt adjustment the camera may be shimmed.
## AIMFRAME
A special frame is made to guide the exact 1:1 setup.
To make an "aimframe" use the optical printer camera (though not necessarily with the optical printer lens) to photograph a target which is especially drawn to contain details exactly coinciding, as seen through the camera eyepiece, with details permanently on the groundglass.
The photograph made while the coincidence is seen is the aimframe.
Every groundglass has some permanent details, even if only its flaws.
The field edge is a poor choice of detail if the mask is thick or if the eyepiece is aberrated at the edge.
Two points of detail are enough for a well~aligned printer, three points for a suspect one.
A reticle made on high resolution film may be attached to the groundglass to add details.
Small patterns of concentric circles and other patterns which self-moiré are ideal.
Also the aimframe can be a negative of the fine-patterned reticle.
For exact 1:1 setup, the aimframe film is registered in the printer gate and the printer camera and lens adjusted to achieve that same coincidence of details, as seen through the eyepiece.
Focusing must be completed before the final adjustment to the aimframe.
It is convenient to incorporate a focusing target in the aimframe.
The aimframe has validity only for the camera in which it was made.
It does not depend on the accuracy of the cameras reflex viewing system, only the stability of the system.
Whenever there is doubt about the validity of the aimframe, such as after a camera repair or because of wear to the film,
The old aimframe can be registered in the printer gate, aimed
on, and photographed to make a newly valid aimframe.
For rotoscoping with primitive contraptions, an aimframe may
be projected and drawn.
This drawing is later used to aim the camera (whose aimframe it was) when photographing the rotoscoped drawings.
The 1:1 accuracy of optical printing with aimframe setups is limited by
1. the precision in the making and then in the use of the aimframe,
2. the precision in the film registration mechanisms of camera and gate,
3. only if the two mechanisms are different, the precision in the film dimensions (perforation and slitting).
Step contact printing, such as by bipacking in the optical printer camera, is a convenient method for making exact 1:1 reproductions.
It must give exposures which are exact 1:1, but there is then some
shrinkage in processing.
Optical printing with the aimframe method compensates for processing shrinkage.
Shrinkage errors are too small to matter with simple printers.