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