228 lines
11 KiB
Markdown
228 lines
11 KiB
Markdown
---
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title: NOTES ON OPTICAL PRINTER TECHNIQUE
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author: Dennis Couzin
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date: "March 1983"
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...
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\pagenumbering{gobble}
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\newpage
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::: {.indexTable}
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|-----|-----|-----|-----|
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| Magnification | 1 | Fades in Original | 14 |
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| Blowup & Reduction | 2 | Chart C: Neutral Density | |
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| Blowup Sharpness | 2 | and Equivalent Shutter | |
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| Printer Lenses | 3 | Angle | 15 |
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| Optical Zoom | 3 | Image Superposition | 16 |
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| Lens Aperture | 3 | Gamma & Bipack | 16 |
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| Focusing | 4 | Incidentally | 16 |
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| Focusing Aperture | 4 | Exposure Compensation | 18 |
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| Focusing Precision | 4 | Special Originals | 18 |
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| Focusing Target | 4 | Texturing | 18 |
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| Depth of Field | 4 | Multi-Exposure | 19 |
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| Bolex Prism | 4 | Multi-Pack | 19 |
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| Bolex Groundglass | 4 | Natural Superposition | 19 |
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| Defocus | 4 | Flashing | 19 |
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| X-Y Adjustment | 4 | Contrast Adjustment | 19 |
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| Exact 1:1 | 5 | Color Image Superposition | 20 |
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| Aimframe | 5 | Weighted Double Exposures | 20 |
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| Framelines | 6 | Dissolves | 21 |
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| Emulsion Position | 7 | Effects Dissolves | 21 |
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| Time | 8 | Fades from Negative | 21 |
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| Fancy Freeze | 8 | Color Exposure | 22 |
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| Fancy Slow | 8 | Testing | 22 |
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| Diffusers | 8 | CC Pack Reduction | 25 |
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| UV Filter | 9 | High Contrast Prints | 25 |
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| IR Filter | 9 | Hicon Exposure | 26 |
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| Green Filter | 3 | Contrast Building Steps | 26 |
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| Filter Location | 9 | Hicon Speckle | 26 |
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| Exposure | 9 | Tone Isolation | 27 |
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| Exposure Adjusters | 9 | Logic of Mask Combination | 27 |
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| Specifying Exposure | 11 | Image Spread and Bloom | 27 |
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| Film Speed | 11 | Mask and Countermask | 28 |
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| Right Exposure | 11 | Reversal/Negative Fitting | 28 |
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| Generations | 12 | Feathered Masks | 29 |
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| Bellows Formula | 13 | Image Marriage | 29 |
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| Fades | 13 | Mask Blackness | 30 |
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| Log Fade | 14 | Hicons from Color Originals| 30 |
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| Bolex Variable Shutter | 14 | Hicon Processing | 30 |
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| Linear Fade | 14 | Optical Printed Release Prints | 31 |
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| Other Fades | 14 | Ritual and Art | 31 |
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:::
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\newpage
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\pagenumbering{arabic}
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\begin{center}
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\textbf{NOTES ON OPTICAL PRINTER TECHNIQUE}
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DENNIS COUZIN
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March 1983
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\end{center}
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An optical printer is a device for photographing the frames of one film so as to make another film.
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****
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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).
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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.
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The camera can be an ordinary cine camera, less its lens, and the gate can be an ordinary cine projector, less its lens.
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Ideally they have identical systems of film registration, as if one were the lens' image of the other.
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The lens can be any bellows mountable lens.
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Ideally it is specially corrected for the small and nearly equal sizes of this object and image.
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The camera and the lens can slide independently to and fro the film gate.
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This adjusted the magnification and the focus of the photography.
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## Magnification
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If the lens is (nominally) midway between the films when one is focused on the other, then the magnification is 1.
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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.
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****
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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.
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Then the magnification is greater than 1.
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At `M > 1` a part of the original frame is photographed at a size which fills the whole of the print frame.
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****
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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.
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Then the magnification is loser than 1.
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At `M < 1` the whole of the original frame is photographed at a size which does not fill the whole of the print frame.
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The remainder of the print frame is filled with a photograph of the gate as it surrounds the original frame (ideally perfectly black).
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****
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For each position of the lens there is exactly one correct (focused) position for the camera.
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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`.
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## BLOWUP & REDUCTION
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The printer gate may hold 8mm film and the printer camera 16mm, or vice versa.
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With a `M = 2` setup an 8mm original frame is photographed onto a whole 16mm frame.
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With an `M = 1/2` setup a whole 16mm original frame is photographed onto an 8mm frame.
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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.
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## BLOWUP SHARPNESS
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A 16mm picture of a flea can be just as sharp as a 16mm picture of an elephant.
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But a 16mm picture of an 8mm picture cannot be expected to be as sharp
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as a 16mm picture of a 16mm picture.
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Pictures differ from things in having very limited detail.
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The 16mm blowup, even if it preserves all the pictorial detail of the 8mm original, spreads it out, so the blowup is less sharp absolutely than the original.
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Under extreme magnification--a microscope objective could be the printer lens--pictorial detail is diffuse and the underlying natural thing, the emulsion, is all that could be photographed sharply.
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But the grains are too small to be sharply imaged with light.
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Here even the natural thing has been photographically exhausted.
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An 8mm original blown up to 16mm and projected will appear sharper than the same 8mm original optically printed onto 8mm and projected.
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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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## BOLEX PRISM
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It isn't a worry.
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There isn't a distinction between RX lenses and non-RX lenses for most any lens which will be used on a bellows for optical printing.
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## BOLEX GROUNDGLASS
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Only for the best optical printer lenses, which will be used at apertures larger than f/4, does the Bolex groundglass need to be reset from its everyday position.
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## DEFOCUS
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To throw an image out of focus without changing its size, if printing at 1:1, move the camera a distance and the lens 1/2 this distance, in the same direction.
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## X-Y ADJUSTMENT
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Besides its to and fro movement the lens has lateral movements.
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These adjust the position of the original frame's image on the print frame.
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For example, if the lens is raised a bit...
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****
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At 1:1 moving the lens up a distance d raises the viewed field by twice d.
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Likewise for down, right, and left.
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At `M > 1` lateral adjustment effects a scan of the original frame.
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This is not geometrically equivalent to a pan, bad it been made in the original photography.
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On simple optical printers the only lateral adjustment is of the lens (rather than the heavier camera or gate).
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This is geometrically adequate.
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But the J-K adjustments are even too flimsy for a lens.
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It helps, after they are set, to gently tap the lens, so it finds a stable position, and then to readjust if necessary, etc., etc. |