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Optical printing - base or emulsion?


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#1 John Lightfoot

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Posted 06 November 2005 - 06:23 PM

I?m working on an Oxberry optical printer, reproducing shots onto kodak 7234 from older, often very scratched up films and getting very mixed results. Hopefully somebody here has some advice?

My question is, is there a preferable side of the film to have facing the camera lens on an optical printer to minimize scratches? The tests I?ve shot (with the base side facing the camera) have so far looked like the scratches had been accentuated - a lot. These are old films so I know to expect a little surface wear, but what I'm getting seems extreme.

Would the level of diffusion on the light source effect this as well?

Any suggestions, help or advice? Thanks?
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#2 Charles MacDonald

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Posted 06 November 2005 - 08:09 PM

My question is, is there a preferable side of the film to have facing the camera lens on an optical printer to minimize scratches? The tests I?ve shot (with the base side facing the camera) have so far looked like the scratches had been accentuated - a lot.
Would the level of diffusion on the light source effect this as well?


I think this is where the concept of "liquid gate printing" come from.

If the scratches are on the base, and you are shooting from the base, you are shooting THROUGH the scratched film. I would (AS a still photographer mind you) expect that if you could shoot from the emuslion side, and use a VERY WIDE lens opening, you might get the emuslion in focus, and try to get the scratches OUT of focus, and out of the picture. If you can provide a disfusion light source, you may also be ahead. IN stll enlargers the colour heads which are disusion sources, are knon to show fewer negative defects than Condensor heads.

For stills you used to be able to gte "edwal no scratch" which is a liguid with an index of defraction simlar to film base. The Liquid gate idea uses the same idea by immersing the film in dry cleaning fluid.
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#3 Dominic Case

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Posted 06 November 2005 - 09:23 PM

The emulsion orentation in optical printing will determine the geometry of the final image. The correct position (emulson or base facing the lens) depends on the material you are printing from, and what you are producing. It's about A-type or B-type geometry (often called A-wind or B-wind). This is more critical than scratches.

Original negative is B-type (it reads correctly with the base towards you). When you make a contact print, it is A-type (reads correctly with base away from you, emulsion towards you).

If you have an A-type print or fine-grain pos, then you would need to have the emulsion facing the lens to make a B-type neg. If you turn it round, the resultant neg would be A-type and you would not be able to cut it in with other camera material etc).

Regardless of which way the film is in the gate, you must focus on the emulsion side of the film. Scratches on the base side will be marginally out of focus, but if they scatter light, they scatter light.

Optical printers work with specular light, so scratches will indeed be emphasised compared with contact printing. The best way to mimimise the effect (barring wet gate, or applying a laquer of the sort mentioned) is to use as much diffusion in the light source as possible. Unfortunatley this will cut down the brightness and probably slow you down - but that's the trade-off.
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#4 John Lightfoot

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Posted 08 November 2005 - 11:22 AM

Thank you for the responses. The base/emulsion and A wind/B wind options kind of make my head spin, but I think diffusion will really help. I recall that JK Optical printers generally use a piece diffused glass between the projector and camera. I haven't been using one on the Oxberry, however. We'll see how it looks when I get the next batch of tests back from the lab.

Thanks again.
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