"Fogged" 4x5 as ND filter?

[poco]

So I've got some old techpan in 4x5 and I was thinking of exposing a few sheets to uniform light, developing to different densities and holding the result in front of my taking lens as different grades of neutral density filters. Is this a totally hare-brained idea? I regularly shoot through Ilford multicontrast filters as replacements for yellow and red filters and am satisfied with the results, so I don't see why shooting through the fine grained techpan shouldn't work. Or...?

[Louie Powell]

I guess I would need to be convinced that the fogging would be truly uniform before I would be willing to use fogged Techpan as an ND filter.

But I would not be at all hesitant to fix out the undeveloped film, wash and dry it, and then use it for dye-dodging negatives.

[poco]

Thanks, Louie.

I think if I throw a long lens onto the camera to guard against fall-off and shoot unfocused onto a piece of mat board, uniformity should be adequate. Then it's just a matter of even processing.

I'll give it a shot, anyway.

[Mark Sampson]

Tech Pan is discontinued, and being slow, should be good well past the expiration date. It might be easier just to find some Wratten ND gels on ebay and make pictures with the film.

[Helen Bach]

Here is what Kodak say in the Photographic Filters Handbook:

“Photographic film, uniformly exposed and processed, makes a good and relatively inexpensive attenuator for visible and infrared use. Because scattering is rather high, you cannot use this type of attenuator in an image-forming beam.”

Best,
Helen

[poco]

"“Photographic film, uniformly exposed and processed, makes a good and relatively inexpensive attenuator for visible and infrared use. Because scattering is rather high, you cannot use this type of attenuator in an image-forming beam.”

"cannot?"

Hmmm... sounds like a challenge to me.:p

Gonna try it with a couple sheets anyway and see what I get.

[C. D. Keth]

It works. I made a set of vignetters to fit a 4x5 mattebox on a film camera this way.

[Helen Bach]

"cannot?"

Hmmm... sounds like a challenge to me.

Yep, sounds like it to me as well.

Chris,

Was there any degradation in the darkened parts of the frame with your vignetter, or didn't it matter?

Thanks,
Helen

[roteague]

ND filters are cheap. Why go through this effort?

[poco]

Robert,

"Cheap" is relative to one's means. Besides, worst case is I'll learn something or other by trying it.

[Jim Jones]

The problem of scattering when using photographic film as a ND filter is lessened when the filter is very close to the film plane. You might even load the filter, emulsion to emulsion, in the film holder. If the filter is exposed to an evenly lit subject with no detail or texture, and developed to a gamma of about 1, it might serve as a center filter.

[Nathan Potter]

Helen and Jim are right about the scattering from film based NDs'. As the silver grain size dimensions come within the range of the wavelength of visible light each grain scatters the incoming rays to some degree so the contrast of the image on film will be reduced. Also depending on the size distribution of the grains the blue part of the spectrum will be scattered more than the red part, esp. for fine grain film like techpan. Thus the film ND filter can become slightly reddish and no longer strictly neutral. This can be measured using a visible light spectrophotometer. But maybe its' not too bad for your purpose. An experiment is worth a thousand words. There is a bit more detail in the reference below.

W. Thomas Jr.(Eastman Kodak Co.), "SPSE Handbook of Photographic Science and Engineering", John Wiley and Sons, 1973, See pp. 951 and 952

[Uusilehto]

Robert,

"Cheap" is relative to one's means. Besides, worst case is I'll learn something or other by trying it.

That's if you buy glass filters from the likes of Hoya and B+W. I think Robert was talking about gel ND filters. A lot cheaper and not that big of a burden to use when you're already lugging around a large format setup.

[Brian Ellis]

Robert,

"Cheap" is relative to one's means. Besides, worst case is I'll learn something or other by trying it.

Good attitude, the history of photography is riddled with things learned by mistakes. We wouldn't have solarized photographs if Man Ray hadn't accidentally dropped his film on the darkroom floor while the lights were on. On a more mundane level, we wouldn't have Heico if the guy who created it hadn't washed his film in salt water while stationed on a Navy ship. Who knows, maybe you'll come up with images that turn out to be wildly popular, you can call them "Pocographs" and become rich and famous.

[poco]

He he.

I was calling my photos Lightleak-o-graphs, but pocographs sounds better.

[C. D. Keth]

Yep, sounds like it to me as well.

Chris,

Was there any degradation in the darkened parts of the frame with your vignetter, or didn't it matter?

Thanks,
Helen

In my tests there were some sharpness problems due to scattering, but the effect was essentially null because the image was too dark to make the call by the time you could notice a loss of detail.