tri-color photography with oneshot camera: exposure?

[Havoc]

So I now have 2 oneshot tricolor cameras. And I really would like to use them (at least once to prove it can be done). So I'd like to get a sensible idea about exposure for this.

The camera splits the incoming light in 3 paths going to 3 negatives: each one gets 1/3 of the light so that is (1 + 2/3) stop loss. Correct?

Each negative has a filter (25, 47B and 58) and those have a factor of 2.5-3. Again this gives a loss of (1 + 2/3) stop. Correct?

So as a start I should compensate my measured exposure (3 + 1/3) stop or multiply exposure time by 8 to 9. Correct?

I know this is probably only a very rough approximation but I do not have much film in the size needed, I need to get started somewhere.

[EarlJam]

Curtis recommended 1/100 at F7 for daylight exposure with Super XX. If my math is correct, that's roughly minus 2 stops from "Sunny 16", so your estimate of 1-2/3's stop seems correct. I made a PDF of a 1947 Curtis price list, which has quite a bit of information on the process, and will send you a copy if you like; PM me with your email address if interested.

[sanking]

So I now have 2 oneshot tricolor cameras. And I really would like to use them (at least once to prove it can be done). So I'd like to get a sensible idea about exposure for this.

The camera splits the incoming light in 3 paths going to 3 negatives: each one gets 1/3 of the light so that is (1 + 2/3) stop loss. Correct?

Each negative has a filter (25, 47B and 58) and those have a factor of 2.5-3. Again this gives a loss of (1 + 2/3) stop. Correct?

So as a start I should compensate my measured exposure (3 + 1/3) stop or multiply exposure time by 8 to 9. Correct?

I know this is probably only a very rough approximation but I do not have much film in the size needed, I need to get started somewhere.

I would suggest about +3 1/3 stops for the Red and Green negatives, and + 1 2/3 stops for the Blue. Develop the R and G negatives for about the same time, the B negative about 50% more.

Including a neutral tone reference, say a B&W step tablet, would be useful in gray balance later in processing.

Sandy

[Drew Wiley]

Are these new filters or original? And what film will you specifically be using? It makes quite a difference. And are any ND filters also involved? Correcting via lens stops will give you different depths of field, so another solution would be preferable. If you have correctly identified your three respective filters, the blue will be much more dense than the other two. One interesting trick is to use TMax 100 for red and green, but TMax 400 for the blue, since the curves are similar even through deep separation filters, though you might have to cut your own sheets to proper size. Super XX hasn't been made for a long time now, and it was grainy, and did have quite a problem developing enough blue contrast per se.

[Drew Wiley]

It takes quite a bit of work and a fair amount of film to learn how to get a balanced set of negatives. If the filters are original, some fading is inevitable and will make things a bit trickier. You didn't state which size camera you have, but Ilford FP4 might be available in your size and is their best product for color separation use, though it too will need extra exposure as well as longer development for the blue filter.

[Havoc]

I was thinking on just using the original filters just in order to know everything more or less works. If that is the case I would replace them by LEE color separation filters as they are damaged. No ND filters unless there are some inside the camera. But I doubt that is the case.

I would correct with the exposure time. But I need a startpoint for the exposure.

Camera is a Devin 6.5x9 so I have to cut 4x5 sheets. I have at the moment only FP4+ around.

But I came to the conclusion that there is a problem with the film holders. One of them is a 6.5x9 but the others are 2.25x3.25... So I first have to source another set of film holders.

[Drew Wiley]

Freestyle has 2.25X3.25 FP4 in stock right now, but it's hard to say how much longer it will be available until Ilford starts up again after the virus hiatus. I'd just stick with FP4 rather than try to learn multiple films. If you do need to replace filters, don't use any of the bottom-tier Lee polyester ones - they're optically poor.

[Duolab123]

I love this. A lot of what is so beautiful about analog photography is the incredible technology.

Every now and then I will spot a real Technicolor film on TCM, I just can't imagine what these productions involved. Mind boggling.

One shot 3 negatives. :o

[Havoc]

Freestyle has 2.25X3.25 FP4 in stock right now, but it's hard to say how much longer it will be available until Ilford starts up again after the virus hiatus. I'd just stick with FP4 rather than try to learn multiple films. If you do need to replace filters, don't use any of the bottom-tier Lee polyester ones - they're optically poor.

Only issue is that 6.5x9 isn't 2.25x3.25 so I would need 2 different sizes of film right now. It will have to wait until I can get 3 identical 6.5x9 film holders. Cutting film in the dark is one thing, managing cutting 2 sizes and 2 sizes holders is another (read: far above my ability).

What filters would you advise then? I got the LEE polyester tri-color set. https://www.leefilters.com/index.php/camera-directory/camera-dir-list/category/tricolour Advantage is that I can get them new from almost any shop.

Problem is they are only 100x100 so a little too small to replace those in the National-Photocolor camera (3.25x4.25).

[Drew Wiley]

Well, you could use that set just to fool around with. But like I already hinted, polyester filters are not optically ideal by a long shot. Also, if 25 red and 58 green are employed, the logical complement would be 47 blue, and not 47B blue, which is distinctly denser and would require more exposure.

[Havoc]

The original filters are indeed marked 47, not 47b. As it is a one-shot, I can not give blue more exposure than the others unless I start adding ND filters in the red and green path.

Ok, let's take this a bit further. Right now the filters are some non identified material that is sandwiched between 2 glass plates. Don't know what happened to it, it looks like it is delaminated (which sounds plausible after 70+ years). I guess it is a gelatin filter. The LEE filters are thin polyester ones, so I'll need to make a support for them. Right now I was thinking of making a little frame to clamp them between. Another idea was to glue them to a thin glass plate but only a single one. No idea how I'm going to avoid bubbles in that case. I'd like to find a way not to have to glue to the filters.

IF I could find massive glass filters I'll take them but so far I haven't been able to find any. I cannot even find massive polycarbonate ones.

[Drew Wiley]

How much exp per filter is going to be directly related to the specific film involved, the differential length of exp if recip failure set in (at long exp), and the fact that in every case, the blue separation will need significantly more exp than the R&G due to the blue filter being significantly denser. Some kind of ND option has to be in place either on the pellicles or along with the filters to get a balanced set. People who have refubished these cameras have gotten custom coated glass filters from Hoya. There are other options too, but all of them relatively expensive. You could get a filter twenty feet across if you knew where to look and had enough money. Even old Wratten gels were made in 6 inch squares.