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NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md

@@ -124,3 +124,72 @@ An 8mm original blown up to 16mm and projected will appear sharper than the same
 If the blowup optics are good this is even true when the 1:1 printing is by contact.
 Likewise for 16mm to 35mm. 
 (This is all due to the print film being in effect twice as sharp and half as grainy in a bigger frame.)
+
+## PRINTER LENSES 
+
+A lens well-corrected for `M = 1` is less well-corrected for `M = 2` (or `M = 1/2`).
+A lens well-corrected for `M = 2` is
+less well-corrected for ` M = 4` (or `M = 1/2`).
+Etc.
+(Floating elements improve this.) 
+A lens well-corrected for `M = 1` for a larger format is lees than ideal for `M = 1` for a smaller format.
+With such specialization (and expense) in optical printer optics what is the hope for the $50 50mm enlarger lens, optimized for `M = .1` and much too large a format?
+Not bad, provided the sharpest aperture is found and heeded and focusing technique is good.
+Also, for `M != 1` an asymmetrical lens should be mounted the right way, which is usually with its smaller glass facing the smaller image.
+
+A very sharp cheap printer lens is the Canon Macrophoto 35mm f/2.8.
+
+## OPTICAL ZOOM
+
+Optical printers do not use zoom lenses, although they could.
+An optical printer zoom is made by moving the camera and lens each frame, so as to vary magnification while holding focus.
+It is a dolly shot!
+A dolly shot is equivalent to a zoom for a flat subject.
+
+Geometrically this zoom can be identical to a zoom had it been made in the original photography.
+It can also be deviant, by tracking not to the center of the frame.
+
+Pictorially the zoom gets grainy, showing that it was not made in the original photography.
+
+Rather than focus at each frame, camera and lens positions can be precharted for, say, every 10th frame, and the other positions interpolated or computed.
+On the J-K, counting the turns of the lead screw is a means of repeatable
+positioning.
+A follow-focus mechanism is a boon to optical zooms.
+
+The rate and course of zooming is a factor of style, as it is in original cinematography.
+
+## LENS APERTURE
+
+For picture taking the printer lens should be at whichever aperture gives the sharpest pictures.
+This is found in tests.
+If a lens must be stopped down past f/8 to reach optimum it is a terrible printer lens.
+
+## FOCUSING
+
+Printer focusing procedure is different at different magnification.
+At 1:1 the camera, not the lens, is moved for focusing.
+Only at magnifications greater than about 1.4 is it better to move the lens for focusing.
+Near the 1:1 setup lens motion has no focusing effect.
+With the camera fixed in its 1:1 position lens motion: adjusts magnification between about M=.96 and M=1.04 (at f/5.6).
+
+## FOCUSING APERTURE
+
+With all but the best optical printer lenses either (1) focus at the taking aperture or (2) focus at a larger aperture and then shift focus by a pre-established distance before taking.
+This "fudge-factor" is found in film tests.
+
+## FOCUSING PRECISION
+
+Especially when focusing stopped down, focus many times (perhaps 20) and set an average position.
+
+## FOCUSING TARGET
+
+Use whatever target is found easiest to focus on.
+One caution: the fudge-factor is target dependent.
+Very fine resolution targets may require different fudge factors than coarser targets do.
+
+## DEPTH OF FIELD 
+
+At indicated f/5.6 there is already more than enough depth of field for a bipack, at 1:1.
+Also it is unnecessary to refocus when adding the second film.
+Likewise when a single film is reversed emulsion to base.
+At larger apertures and at larger magnifications depth of field is less.