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  #1  
Old 5th February 2009, 08:57 PM
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Default Colour head or under the lens filters?

I have an enlarger with a colour head but use under the lens filters.Is there any differnce in the contrast achievable? The under the lens filters are Ilfords.
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Old 5th February 2009, 09:06 PM
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I don't think you can be sure without doing some side by side tests of the two methods. Other factors may come into play such as paper and developer. I use a colour head, so I guess I'm biased, others here prefer under lens filters.
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Old 5th February 2009, 09:06 PM
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You will usually get a higher maximum contrast with under-lens filters. My LPL C7700 for example can manage a maximum contrast equivalent to about a grade 4 Ilford filter. Minimum contrast is about the same for both systems.
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Old 5th February 2009, 09:53 PM
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John, also bare in mind that not all VC papers will give you a true grade 5. Foma MG for example will only go to grade 4. Ilford papers will stretch to 5.
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Old 5th February 2009, 10:26 PM
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John, I use both.
The Colour head on my Meopta Magnafax and under the lens filters on my smaller Kaiser enlarger.
There are pros and cons to both, with the colour head I like the small changes in contrast (with a little practise) you can achieve. With the filters they are quick and easy to use but lack the constantly variable grade changes available with the colour head.
A good point was made about maximum contrast for any giben paper, colour heads can't always manage G5 especially with a diffuser head.
Good luck

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Old 5th February 2009, 11:17 PM
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YES and NO. The resulting contrast of VC paper is dependant not only on the filters used but also on the contrast of the negative being printed. In the real world there are three parts to the equation and not two which a lot of people seem oblivious to. And if you take paper developer into the equation, there are four parts. In the theoretical world, there are only absolutes and people measure resulting contrast by using a static negative contrast and comparing the effect of dichroic filters compared to discreet filters. Doing that, you may mistakenly come to the conclusion that dichroic filters can't achieve G5

However, in the real world, if you calibrate your film dev to give enough negative contrast to allow a low enough setting of dichroic filtration to achieve G2 on paper, then you have sufficient extra dichroic filtration available to allow 3 full extra grades on paper from that same negative assuming the paper is capable of it. Print that same negative using an Ilford G5 negative and you would get around a G6 on paper if the paper was capable of it which it probably isn't.

Using Dursts figures for Y+M filtration for G2 gives about 1 contrast grade less than ilfords filters do. But calibrating the neg development to suit the durst Y+M figures for G2 allows a full 3 grades extra contrast on paper and does achieve G5 on paper with ilford papers.
And because of the extra neg development required to calibrate to ilford Y+M figures for G2, you also get better film speed so using dichroic filters is probably a better option unless you are doing split grade printing where ease of changing from max yellow to max magenta may make under the lens filters more appealing.
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Old 6th February 2009, 09:11 AM
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"Grade" has always been a somewhat confusing term since different manufacturers historically used different systems for specifying paper contrast. There is now an ISO standard for paper grade which specifies the range of contrast (measured in ISO(R) units) corresponding to a particular grade. There are 30 ISO(R) units per stop of contrast, or 100 ISO(R) units per 1.0 log.D of density.

It is therefore possible to compare colour filtration systems directly by printing a step wedge onto the paper in question using different filtration. If you do this for Ilford Multigrade IV FB, then a true ISO grade 5 is achievable with Ilford under-lens filters, but most colour heads (including mine) cannot manage much more than a true grade 4. The filtration settings that Ilford publish for use with colour enlargers match their under-lens filters reasonably well when used with Ilford papers, but may not when used with other papers.

The only way to find out what "grade" of contrast you actually get at any particular filter setting and with any particular paper is to test it by printing a step wedge. Negative contrast does not affect absolute paper contrast at all, but what it does affect is the contrast you'd get on a print made at any specific filter setting. Variable contrast paper allows you to match the paper contrast to that of the negative, rather than the other way round (which was why the Zone System and similar were invented, because paper contrast was pretty much fixed so you had to adjust the negative to fit it).

Whether you choose under-lens filters or the filters in a colour head really comes down to convenience. Dichroic filters are continuously variable so if a negative requires a "grade 2.8" for example, you can get that by adjusting the filters whereas with under-lens filters you're limited to half-grade steps. Or you can have the best of both worlds by using under-lens filters and dialing in a wee bit of Y or M on the colour head if required to fine tune the contrast. That way you get your true grade 5 as well - if your negs are soft enough to need it .
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Old 6th February 2009, 10:19 AM
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Wandering off topic slightly, but it’s always puzzled me why, after spending good money upgrading our camera lens from the standard bottlebase normally supplied, and buying the best enlarger lens man can make; we then resort to waving a piece of coloured gelatine in the lightpath to our print.

Sorry John.
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Old 6th February 2009, 10:25 AM
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The filters are thin enough and sufficiently out of focus to have negligible, if any effect. I've certainly never noticed any deleterious effects using them.
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  #10  
Old 6th February 2009, 10:28 AM
Dave miller Dave miller is offline
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Quote:
Originally Posted by RH Designs View Post
The filters are thin enough and sufficiently out of focus to have negligible, if any effect. I've certainly never noticed any deleterious effects using them.
Is that because of the bottlebottoms you print through? Point taken.
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