BW VC paper contrast control with color head

[Anupam Basu]

I recently got a Chromega 4x5 enlarger and am trying to figure out how to change contrast with it for variable contrast papers. The manual only lists M and Y channel values for grades 1 to 3. Is it not possible to go above or below that with the color filters? I assume the C channel just needs to be set to zero. Is this correct. Also, how does exposure need to change between different contrast grades - my Ilford filter set needs double exposure above grade #3 - is it the same here?

Any info on using color filters for BW contrast control would be useful. Finally, am I better off using plain filters with the head set for unfiltered light?

Thanks,
Anupam

 

[Nick Zentena]

Usually the paper you use will publish a list of settings to get you started.

Two colour numbers [Y/M] are normally speed matched. Single colour numbers Y or M aren't speed matched.

You should be able to get over grade 4 unless the filters are faded.

The colour filters are a lot easier to use once you get used to them. They also make split filtering easy.

Cyan can be used for ND I guess but I've never had a need.

 

[srs5694]

Two colour numbers [Y/M] are normally speed matched. Single colour numbers Y or M aren't speed matched.

In other words, you'll often be able to find two tables from a paper or enlarger manufacturer. One includes both magenta and yellow values for a given grade and the other provides just magenta or yellow filtration (the other is set to "0"). With the first (two-value) filtration, exposure should be constant no matter what the filtration setting, but most exposure times will be longer than with the single-value table. With the single-value table, exposure will change with every change in filtration, but you'll have shorter overall exposure times.

As background and elaboration, B&W filter sets are designed with appropriate amounts of ND filtration to keep exposure constant. When using a color head, if you want constant exposure across grades, you've got to use both magenta and yellow filtration at specific levels to achieve the same effect.

Cyan can be used for ND I guess but I've never had a need.

Actually, cyan filtration (which removes red light) has no effect on a finished B&W print with most VC papers, at least in theory. In practice, the filter might block some blue or green light, or the paper might have some sensitivity to red light; in either case there'd be a (probably very) small effect on the print. For most VC B&W papers, you can achieve ND filtration by increasing both magenta and yellow filtration.

 

[Neal]

Dear Anupam,

Assuming you have a Chromega Dichroic you should be able to obtain a wide range contrast range from a good paper. If you have a Dichroic II, you are in really good shape. Personally, I suggest that you forget about paper grades and simply add magenta to increase the contrast and yellow to decrease.

Enjoy your enlarge.

Neal Wydra

 

[pentaxuser]

These posts have caused me to think again in first principle terms about printing with dichroic heads using the Y and M dials.

I think it is true to say that while in the middle range of grades the dual filter system keeps the exposure much the same, it is not exactly the same. Using a Phillips analyser and keeping the spot reading on the same area of the neg, I noticed that the exposure reading changed slightly at each grade, close to the middle grades but more appreciably the further away from about grade 2.5 you were and indeed at grades 0 and 5 the Ilford tables exclude almost all M at grade 1 and in fact all Y at grade 5 and become the same as using a single filter.

From what one post has said, it would seem that if grade 3 was say 30Y and 40M and you wanted additional exposure, say 1 stop more, then 60Y and 80M would give you this without altering grade.

Have I got this correct?

As VC paper is to all intents and purposes unaffected by C then simply adding C without altering Y and M would also achieve increased exposure. If this is correct then this may be the better alternative to increasing both Y and M by the same factor, in that at higher grades you'd run out of Y amd M if you needed to double exposure whereas you'd have the full range of C available.

pentaxuser

 

[Nick Zentena]

Remember the tables are just a starting point. Personally I suggest going with what Neal stated. Forget grades and adjust until you like.

Just because the table claims X/Y is grade 3 doesn't make it so. You could spend the time testing to figure out the actual grades but for most the grade doesn't matter. The beauty of a color head is if the print looks best with grade 2.75 instead grade 3 or grade 2 no problem.

 

[srs5694]

From what one post has said, it would seem that if grade 3 was say 30Y and 40M and you wanted additional exposure, say 1 stop more, then 60Y and 80M would give you this without altering grade.

Color heads are usually calibrated so that a change of 30 units on all three dials corresponds to a change of 1 stop on color paper. If that relationship holds with B&W paper, it'd mean you'd need to change the magenta and yellow filtration by 30 units to create a 1-stop change in exposure, so if you've got the look you want with 30Y/40M but want to double your exposure time, you'd change that to 60Y/70M.

This is largely theoretical, though. In practice, the filters might not exactly match the sensitivity of the papers' layers, so you might need to tweak these values. I've gotten good results with this as a rule of thumb with my Philips PCS130 with PCS150 control unit, but it's unusual in that it uses an additive system (separate red, green, and blue bulbs rather than a single bulb with cyan, magenta, and yellow filters).

As VC paper is to all intents and purposes unaffected by C then simply adding C without altering Y and M would also achieve increased exposure.

As you say, VC paper is unaffected by cyan filtration; therefore, adding cyan filtration will not affect exposure. Again, though, this is theoretical and based upon assumptions of perfect filters and paper that's 100% insensitive to the light that's being removed by the cyan filter. In practice there might be a small effect, but it'll be small, and I'd expect it would affect the blue- and green-sensitive layers differently, resulting in a slight contrast shift.

If you don't believe me, do some tests. I've done so and found no effect of even massive "cyan filtration" -- that is to say, turning off the red light on my PCS150.

 

[David Brown]

Assuming you have a Chromega Dichroic you should be able to obtain a wide range contrast range from a good paper. If you have a Dichroic II, you are in really good shape. Personally, I suggest that you forget about paper grades and simply add magenta to increase the contrast and yellow to decrease.

I second this suggestion. I have the Dichroic II. With Ilford MG, 5M is gr 2.5, and 25M is gr 3 (IIRC). But, sometimes a negative needs 10M. So there ya are.

 

[Gil]

Anupam,

Here is a guide to help you with the filters.

0 filter( 100y +15m)
1/2 filter( 80y + 20m)
1 filter ( 55y +30m)
1 1/2 filter (45m +40m)
2 filter ( 40y +45m)
2 1/2 filter ( 30y + 50m)
3 filter (25y +60m)
3 1/2 filter (10y +75m)
4 filter ( 05y + 90)
4 1/2 filter (05y +130m)
5 filter (05y + 200m)

Gil.

 

[Maine-iac]

I recently got a Chromega 4x5 enlarger and am trying to figure out how to change contrast with it for variable contrast papers. The manual only lists M and Y channel values for grades 1 to 3. Is it not possible to go above or below that with the color filters? I assume the C channel just needs to be set to zero. Is this correct. Also, how does exposure need to change between different contrast grades - my Ilford filter set needs double exposure above grade #3 - is it the same here?

Any info on using color filters for BW contrast control would be useful. Finally, am I better off using plain filters with the head set for unfiltered light?

Thanks,
Anupam

Why don't you try split-grade printing to see how you like it?

In short, (you can find longer explanations in this forum) you do a test strip in 3 second increments of a well-exposed negative using only the M filtration, set to its maximum. Pick the strip that has the desirable amount of detail in the darkest shadows. This is subjective, of course. Someone else might like slightly less dense or more dense shadows. Let's say, for example, that the darkest shadow area in which you want to see texture/detail is 10 seconds at f/11 at full magenta.

Then repeat the test strip procedure with the same negative on a new sheet of paper, this time, using maximum yellow filtration. Look for the brightest highlight that just barely contains texture/detail. (Remember in both cases, there will be a dry-down effect of 4-8% depending on the paper, and allow for this.) Let's say, for example, that on the test strip 6 seconds at full yellow gives you a bright highlight that has the desired amount of texture/detail.

Now, run a sheet of paper, giving it two exposures, one at 10 seconds full magenta and another at 6 seconds full yellow.

This should give you a work print that is very close to perfect on the first try. You may need to adjust one or both of your exposures to fine tune it, and you may identify areas of the print where you need to burn or dodge using both or one of the two colors.

A rule of thumb, easily broken however, is that if you want to increase or decrease overall density without changing the contrast, burn or dodge proportionately with both M and Y filtration. If you want to change contrast, burn proportionately with one or the other, i.e., for a harder tone, use only magenta when you burn a particular area; for a softer tone, use only yellow when you burn.

It may be a little tricky at first getting your mind around the concept, but when you do, you will be amazed at how easy it is to come up with a good work print on the first try, so long as your paper is the same. Changing papers will necessitate running new test strip prints to establish base times for that paper.

It's a little more time-consuming than a single exposure using a combination of M&Y filters, but it makes the tones more luminous, in my opinion, and is really easy and consistent. I've been doing it for years with excellent results. Les Maclean has some articles on this too. Our techniques may differ slightly, but essentially, we're doing the same thing.

Larry

 

[tleirtro]

Here's a link to an Ilford paper with conversion tables for various enlargers.

Thor Egil