Rosco Gels for Contrast Filters ??

[Worker 11811]

I just got a Beseler 23C enlarger and I am looking for a set of contrast filters for it. I can certainly get a set of them on line but I just had a thought...

I work in a theater. It's both a movie theater and a legitimate theater. Consequently, we have scads and scads of Rosco gels floating around. We have a whole drawer full of scraps we use for small projects and, sometimes, we even throw out gels because we don't have room for all the scraps we accumulate.

That's what got me thinking. Does anybody have a list of which numbered Rosco gels can be used for contrast filters? We also have Lee and Gamcolor filters as well.

We could always order certain colors of gel if we need it but my main thought would be to put some of the stuff we have lying around to good use instead of tossing it out.

 

[Mainecoonmaniac]

You probably could use them if you use the filter above the lens, preferably above your negative because I don't think their of high optical quality. Also you have to figure out the CC value of each gel so you could calculate the desired paper grade. I would invest in a set of filters because it could be too much trouble to figure out the filter values. I prefer Ilford filters. I'm sure Ebay has some on their site. Good luck.

 

[fschifano]

True, you could use them above the lens in a filter drawer. I use the Rosco ND gels to cut down some of the light when my exposure times are too short. They certainly are not made to the standards employed for gels to be used in the imaging path. You may be able to get away with it, but I wouldn't expect to. The biggest problem you'll have is determining the correct mired values to match contrast grades for the particular paper you're using. Since neither Ilford nor Kodak publish these numbers for their filter sets, you're pretty much on your own trying to figure these out. My guess is that you'll waste a heck of a lot of paper doing it - at a cost far more than that of a new 6x6 inch set of Ilford or Kodak variable contrast filters.

You can use these scraps to gel down small on-camera strobes; or, if you have larger sizes, use them on studio type strobes for the same type of effects used in the theater.

 

[Lee L]

Steve Anchell's "The Variable Contrast Printing Manual" talks about VC printing filter sets used by a number of photographers, and includes Rosco gel combinations for different contrasts.

Lee

 

[Mainecoonmaniac]

Hey that's great. What a time and paper saving suggestion.

 

[CBG]

Presuming you can get the right very deeply tinted Rosco (or whatever) filters, you can do very effective split filter printing. There should be a few suitable for your purposes. For split filter printing, you want the strongest blue or magenta gel you have available to get the high contrast emulsion of the paper working. Likewise you want the strongest green or yellow gel you have available to expose the low contrast emulsion in the paper. Essentially one filter is best if it excludes all green light, and the other filter is best if it excludes all blue light. Weaker filters will not give the whole range the paper is capable of.

You'll have to do one exposure with the soft filter, and then a different and separate exposure with the hard filter. Or vise versa, the order does not matter. People will disagree on this, but neither emulsion "knows" what is happening to the other so it does not matter. You have to make two separate timed exposures (unless you want max or min contrast). Just swap filters and reset your timer. With two strong contrast filters, you can't stack the filters to attain an intermediate contrast. An important side benefit is that you can burn and dodge with each filter separately. No single exposure technique offers that.

When you use only the green/yellow filter and no blue/magenta time at all, you have the softest contrast that paper and your yellow/green filter can produce. When you bring the soft filter time down to 0 and use the blue/magenta filter exclusively, you have the hardest contrast that paper and your blue/magenta filter can produce.

I have not tried it, but if your filters are not quite strong enough to max out the hardest and softest contrasts the paper can attain, you may be able to eke a bit more contrast out of the hard filters if you double up two blue/magenta filters on top of each other Ditto the reverse situation with doubling the soft filtration.

There is no reason you should not be able to get all the contrast range the paper has to offer. The only limit is what filters you can scrounge up.

Roscos would not want to be in the image path unless you test and find they happen to exceed their designed specifications. They are not intended to be optically flat They should be above the negative - not just above the lens. Kodak Wratten gels on the other hand are fine in the image path, but will cost more.

 

[CBG]

... The biggest problem you'll have is determining the correct mired values to match contrast grades for the particular paper you're using. Since neither Ilford nor Kodak publish these numbers for their filter sets, you're pretty much on your own trying to figure these out. My guess is that you'll waste a heck of a lot of paper doing it - at a cost far more than that of a new 6x6 inch set of Ilford or Kodak variable contrast filters ...

I don't worry about matching paper grades with split filter printing. I just test for highlights and test for shadow and combine them.

 

[Nicholas Lindan]

The optical quality of theater gels is very good as long as they aren't scratched or wrinkled. To test for aberrations look through the filter while holding it almost edgewise, wiggle the gel around a bit and check that the view stays solid and doesn't wiggle in sympathy. If they pass the wiggle test there will be no problem using them under the lens. You may want to mount filters you use under the lens in cardboard frames to keep fingerprints off the filters and as a measure of scratch protection.

If you look on the Rosco and Lee web sites you will find spectral graphs of all their filter products. You will be able to find deep blue and pure green filters for split grade and a variety of impure colors that will produce intermediate contrast grades. You will not be able to find filters that correspond with the ones in the graded filter set. VC filters don't correspond to CC filters, which are made to match the color sensitizers in color film and color paper. That doesn't stop people from using CC filters, as anything that varies the blue/green light balance will have an effect on print contrast.

The 3x5" filter swatch books in combination with a good 3x3" gel holder can give lots of filtering effects that you can not achieve by using standard photographic filters.

Filters are the most over-hyped and over-priced of all photographic accessories.

 

[Worker 11811]

Well, I know that Rosco #27 can be used for a safelight filter. It excludes just about all light shorter than 550 or 600 nm and it's total transmission is only 4%. IRRC, the Lee Filter equivalent would be #26.

Of course, the usual caveats apply: Not too bright. Not too close and keep the time short.

If I knew the wavelengths that multicontrast paper responded to, I could probably figure out filter sets that would work using Rosco or Lee. I would use the top, above-the-film slot in the enlarger. Call me anal but I just don't feel comfortable putting anything between the film and the paper except the enlarging lens. Besides, I like to keep the lower filter slot available for the safety filter.

I'd like to get that book "The Variable Contrast Printing Manual but there are no bookstores in town which carry any photography books to speak of, digital or otherwise. I might order it some day but, for now, it would be a suboptimal expenditure on my part to buy a book just to get a list of numbers.

 

[Mike Wilde]

Per Anchell's VC Printing Manual, the best blue /green additive filtration suited to split filter printing are Rosco 389 Chroma Green, and Rosco 68 Sky Blue. There will be similar filters available from Lee and GAM.

 

[Mike Wilde]

There are other approaches if you have a cold light i.e flourecsent that produces more blue light.

Anchell provides data from Joe Englander's setup with a cold light head; this same setup could work for you by first including a cinegel colour corrector to shift from your tengsten source to a more daylight response, then experiment with the following setup for more conventional non-split filter printing techniques. As you see, these are mostly cinegel, which is more common in film than theatre, though some theatre lighting designers that do pull from the cinegel line when selecting thier pallet, particualrly in lighting musical theatre for a two colour yellow/blue or green/magenta wash.

3107 ToughY1
389 Chroma Green
3304 Tough Plusgreen (30G)
3315 Tough Half Plusgreen (15G)
3313 Tough Half Minusgreen (15M)
3308 Tough Minusgreen or Roscolus 37 (30M)
3302 Full Bue (80A)
68 Sky Blue

 

[lloyd]

Howard Bond wrote an article several years ago (Photo Techniques) in which he used/tested the magenta and yellow offerings from Roscoe--these work as well,
including under the lens with no degradation.

 

[Worker 11811]

Mike,

You're right. We use mostly Roscolux and, only occasionally, Cinegel.

We've got tons of #68 but none of the others you mention. I suppose I could order the right colors. They only cost about $5.00 per 24" sheet but, at that price, I could just buy the Kodak Polymax filter set and be done with it. Right?

Still, there's no reason I can't try Rosco for the purposes of experimentation.

Is there a place where I can find out what wavelengths of light different multi-contrast papers respond to? With that information I could go through the transmission charts and pick which colors match. If I have a set of filters on hand I could also just go through the swatchbook and find the closest matches and use those as a starting point.

 

[fschifano]

That's the problem, ok. No one releases those numbers for the consumer, or at least I haven't seen them and I can understand why. Those data are probably a closely guarded industrial secret, much the way a chef will not release his seasoning recipes for the speciaties of the house. Aside from detracting from sales of VC filters, the whole thing will get very complicated very quickly. For starters, I don't think that the hard and soft contrast emulsions are exclusively sensitive to blue and green light respectively. I think it's more like the hard contrast emulsion is primarily sensitive to blue light and to a lesser degree sensitive to some green light, while the soft contrast emulsion is primarily sensitive to green light with a lesser sensitivity to blue light. So now you're faced with determining the blue/green ratio for the hard and soft emulsions, and mind you this will be different from one paper to the next and maybe even from batch to batch of the same paper. After that it becomes a balancing act to determine the ratio of blue to green light you'll need to achieve a given contrast grade. If you could find the numbers, it wouldn't be too hard to cobble together something yourself. Without the numbers you'll likely be on a quest for the Holy Grail. Oy! The whole thing makes my brain hurt just thinking about it. Better to just get a set of variable contrast filters and be done with it. Either brand is ok, but I'd probably want to go with the Ilford standard now. The Kodak standard was fine for Kodak papers, and they do work with every paper I've tried. But I think most, if not all, paper manufacturers today adhere to the Ilford standard and you might find them easier to work with.

 

[Worker 11811]

Well, at this point I am thinking strictly in terms of experimentation.

I will buy a set of contrast filters. Probably Ilford. I just automatically think "Kodak" when I think of film products. It's a function of upbringing.

Once I get them I plan to compare them to the Rosco, Lee and Gamcolor swatchbooks just to see how they measure up.
I wonder if I could put them on my scanner and use my computer to make a comparison.

 

[Nicholas Lindan]

...soft emulsion... ...hard emulsion...
​

Ilford (and Kodak's late Polymax) all use 3 emulsions. The emulsions have the same intrinsic contrast, though different DMax's. All three emulsions are equally sensitive to blue. The 'cyan' and 'green' emulsions are equally sensitive to cyan light. The 'green' emulsion is additionally sensitive to green.

See the application note on VC paper on the Darkroom Automation web site.

(please email me if you are seeing a whacked-out font in the above app note.)

 

[Worker 11811]

So variable contrast paper works in a way that's analogous to CMY printing. Right?

Whereas printers use cyan, magenta and yellow inks which, when combined, will produce a gamut of different colors, variable contrast papers use emulsions sensitive to blue, green and cyan which, when combined, will produce a gamut of different levels of black.

Therefore, just as it is possible to mix cyan and yellow ink to produce the color red it is also possible to mix amounts of blue, green or cyan light which will produce a certain density on the paper when it is developed. It's only a matter of discovering what colors the emulsions are sensitive to and feeding them what they want to "see" in order to produce a given result.

Yeah... I know... Easier said than done.

But somebody has to know this or else you couldn't use an enlarger with a dichroic color head to print on variable contrast black and white paper. How do enlarger manufacturers figure it out? (Rhetorical question, really.)

If you haven't already guessed, this is the kind of thing that really makes the gears turn inside my head. Even if I don't figure this out to my total satisfaction, there is knowledge gained. Even if I learn nothing else, I now have a better understanding of how variable contrast paper works. Hopefully, that will translate into me being able to produce better results in the darkroom.

 

[ic-racer]

No need to do two exposures. Rosco sells CalColor filters in Magenta and Yellow CC grades. So, for a complete set pick up 90M, 60M, 30M, 15M and 15Y, 30Y, 60Y 90Y.
The difference between that set, and the Ilford set is that with the Rosco set, you exposure will be different with each filter. So, I don't know if its worth it to you. I'd just pay the extra $ and get the Ilford set.

 

[Worker 11811]

At $5.50 per sheet that comes out to $45.00 for a complete set but you would end up with 12 sets of 6 inch filters or 48 sets of 3 inch filters, leaving you with a net cost of about $3.75 or $1.00 per set, respectively.

You can't beat that with a stick!

For my first few times out of the gate I'll do things by the book and get the Ilford filters. Then when I am ready to experiment I'll get the Rosco.