From 2d9a88cc73147862fdf76a176d0a1a482f016792 Mon Sep 17 00:00:00 2001 From: mattmcw Date: Tue, 26 Jul 2022 14:54:17 -0400 Subject: [PATCH] Added several more sections, no graphics --- NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md | 69 +++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) diff --git a/NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md b/NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md index acb0961..1a138e1 100644 --- a/NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md +++ b/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.