First colour print

[Photo Engineer]

Ed;

Three things you should be made aware of.

First, a change in cc filter does NOT change gamma, it changes relative speed. These two characteristics (gamma and speed) are two different things. One is the slope of the curve and the other is the sensitivity of the layer to light. Only the latter is related to cc filter changes.

Second, in my experience with both Chromega and Beseler heads (I have both and have used many more than those at EK) and my cc filters, I find that depending on filter density a 0.1 change or a 0.5 change takes place with a corresponding fresh filter of whatever sort (CC, CP, Dichro, etc) and gives just about the same result.

When measured, the density and speed change is roughtly equal to the on peak density of the filter as well, regardless of filter. I have measured these on-easel with a spot photometer.

Third, the reason that Ilford gives such data is because the sensitivity of MG B&W paper is quite different than color paper in the green region and therefore responds differently to the magenta filtration factors and blue filtration factors, but color paper has a different response. The CC filters were designed for color paper peak sensitivity.

I have recently posted a wedge spectrogram of Ilford MGIV paper in another thread. If you move the green peak several units to the right on that plot, you will begin to approximate the green sensitivity of modern color papers.

PE

 

[digiconvert]

I've described my setup way too many times-) Do a search. Basically I use Jobo tanks for both film and paper. For tempering I use a picnic cooler with a fish tank heater. To roll the tank I use print motorbase hooked up to a gralab 300 timer. Works just a perfect for paper and film.

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Yes I found your set up when I was considering a TBE - seems a waste of time(TBE not your set up )- and it's one of the things that made me think home processing was a possibility without spending a fortune. So Thank You

As for the other advice thanks a lot - I think I'm going to have some fun !

 

[digiconvert]

I agree, a change of .05 "density change" is supposed to effect a change of .05 gamma...
But that was not what I was saying. The calibration of dichroic color heads ("cc" units) does *NOT* seem to conform to any given standard. As far as I can tell, there is no guarantee that a 5 "cc" change will result in a change of .05 in filter density. Kodak. Leitz, and others do not seem to follow the same linearity - that is why Ilford gives different contrast modification numbers for different enlarging systems.

I can't pretend to understand much of this. I'm a trained lab technician so I always work on the 'suck it and see' methoid - if it works the theory can go hang

 

[Nick Zentena]

If you go the picnic cooler route don't skimp on the cooler. Bigger is better. The downside is it'll take longer to heat up but once it's up to temp it'll hold temp for a long time. Also make sure it's got a drain.

 

[Ed Sukach]

Three things you should be made aware of.
First, a change in cc filter does NOT change gamma...

I feared as much... I did not make myself claer.

The point I am trying to make is that *All enlargers" - more properly, All enlarging fitration systems are not created alike. What serves as 5 cc change in one is not necessarily the same in another.

The example I was thinking about is dervied from the Ilford Filtration Tables, that allow a dichroic head to be used in controlling the contrast of Ilford Mutigrade Paper, from Table 5, in the enclosed data sheet:

To obtain Grade "0" contrast with a Durst (max 170M) head, use 100Y/ 5M as a starting point. For the same contrast, with a Durst (max. 130M) head, use 88Y/ 6M; Kodak, 90Y/ 0M; and Leitz Focomat V35, 105Y/ 12M.
These settings should (~) give light with the same color balance to effect a contrast grade of "0".

In the middle, Grade 2 1/2, Ilford recommends Durst (max 170M), 42Y/ 28M; Durst (max 130M), 35Y/ 31M: Kodak, 32Y/ 42M; and Lietz Focomat V35, 32Y/51M. At Grade 4 1/2, Durst (170M max.), 10Y/ 105M; Durst (130M max.), 6Y/ 89M; Kodak, 0Y/ 150M, and Leitz Focomat V35, 15Y/ 154M.

All these different head settings are calculated to give the *same* mixture of magenta and yellow in the light from the enlarger. The paper itself has little, if anything, to do with it... Which is my point: "All enlarging heads are not equal in "cc" unit correction. My experience, admittedly limited, supports that information. A change of 30 "cc" does not necessarily (in fact, rarely will) result in the equivalent of .30 (one stop) change in the dichroic filters. It will, accurately, in the density control filter of my Omega D5500.