Make a center filter using photoshop

[Paul Schilliger]

Clive, your idea is not bad, but I think the layer of gelatin will act as a soft ening and diffusing filter and produce some interesting effects. Maybe it would be worth trying the other way around (c lear center), this would perhaps produce an interesting portrait and still life filter! Just a thought... never t ried. The best way of going around a center filter is by using a Photoshop technique after the scan, but a center fil ter, when needed, is a worthy investment. They not only produce an even illumination of the film, but they als o protect the lens, from the stray light and parasite reflexions that occur inside the lens with very wide angles i n bright light.

[Clive Kenyon]

Paul, I take your point - but if you can project light through a negative to give sharp results on an enlarger, then why will it not work on a camera?

Answers on a postcard please.

Clive

[Paul Schilliger]

Clive, industrial films have extremely even and accurate layers and even so, the y would produce a diffusion effect if put in front of a taking lens. Older enlargers were equipped with sets of optica l condensers to direct the light and minimize the diffusion effect and produce sharp images. The paper's contrast wil l also reduce the diffusion effect. I am not aware of any modern standard glass plate films available on the market, s o making them yourself by painting a sheet of glass with photosensible emulsion would be far from the standards of a good optical filter, without underminding your skills! But as I said earlier, it could be worth a trial. Why don't you shoot a grey card on a B&W negative, use the neg as a neutral density filter and report here of your findin gs? (Was that too long?)

[Sal Santamaura]

T-max 100 4x5 glass plates are available at around $12.00 each.

[Clive Kenyon]

Well, that's me done folks. I supplied the idea - it's up to you now!

Clive

[Mike Parrish]

Has anyone tried the following:

1. Expose a piece of film against a blank wall with the lens at infinity and f/22 to get the proper pattern. *The formula used to calculate light fall-off may not be very accurate with modern lens formulas.

2. Scan the processed film.

3. Blur the image just enough to kill any grain or noise.

4. Adjust contrast and density as needed.

5. Use an inkjet printer on a blank or UV Wratten gel filter.

6. After testing for accuracy, sandwich the gel filter between optical glass with the proper cement. *I believe many high quality filters were made this way in the "early days", just not center filters... until now :-)

[Paul Butzi]

"Paul, I take your point - but if you can project light through a negative to give sharp results on an enlarger, then why will it not work on a camera? Answers on a postcard please. "

It won't work the way you expect because the sharp results you get when enlarging are the image of the film focused on the paper, and not a point source simply shining through the negative. That's why you need an enlarging lens.

Take a duffer piece of film, fix out all the silver, and dry it. Or, just look through the thin part of one of your negatives. Does it seem like you're looking through clear glass, or some frosted material?

[Mike Parrish]

Ouch...

Actually, gelatin filters carry the very best optical characteristics. Heliopan/B&W sandwiches/glues gel filters between optical glass for many of their very expensive filters even today. So quality isn't the issue unless optical anomolies are introduced by the ink from the printer or if the alignment/gluing are poorly done.

If there is a printer with black ink of optical quality, this should work. That's all I really meant to say. If anyone out there is aware of such a beast please let me know.

I've seen the highly prized Heliopan center filters made in this manor, though I don't know how they make the graduated center. It makes you wonder, doesn't it?