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  1. #1
    JackRosa's Avatar
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    Contrast Achieved with Dichroic Filters

    Anyone out there with a Chromega F (8x10) head who has conducted tests to see what contrast can be achieved at maximum Magenta (170 units)?

    I know I know, … it all depends upon paper and developer.

    The reason I am asking is that using Ilford VC paper and both, Ilford Mutigrade developer and Formulary's PD-130 (1+1) I was never able to come close to the contrast achieved via an under-the lens Ilford Grade.

    Recently, I conducted a test using PD-130 [diluted 1+1] and Oriental paper and wow! … the results are pretty close to what I get with the (under the lens) Grade 5 filter. I am wondering whether the filter has faded; I could not believe me eyes.

    Details: developed paper in PD-130 (1+1) for 1 minute at 70F.

    Has anyone had a similar experience with this Omega head and a paper/developer combo??
    Jack Rosa

  2. #2
    ic-racer's Avatar
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    The first obvious question is to ask if you have the Dichroic head or the older Acetate filter head? If it is the Dichroic head, have you have checked things like light leak around the filter and ensure that the filter totally covers the light when set to 170?

    How are you doing the test? When I checked some Omega D5500 magenta filters from the 1980s and 1990s against the #5 Ilford using a standard 21 step wedge and Ilford MG FB, it was difficult to detect any difference.
    Last edited by ic-racer; 02-12-2014 at 02:02 PM. Click to view previous post history.

  3. #3
    Jim Noel's Avatar
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    You have begun to learn the truth about printing VC papers with dichroic heads.
    When accurate tests have been run most have indicated the maximum achievable contrast range is approximately 1 1/2 - 3 1/2.
    When I was using a head like yours I found these tests to be accurate.
    [FONT=Comic Sans MS]Films NOT Dead - Just getting fixed![/FONT]

  4. #4
    JackRosa's Avatar
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    Different Opinions, I see

    If I am interpreting IC's insight and Jim's insight correctly, IC says max. magenta gives equal results to Ilford # 5 and Jim says max. magenta gets you to only 3.5.

    IC: I am using the newer (dichroic) filters. No leaks, for sure nw I made adjustments) but it is possible I had leaks before. This may very well be the culprit.

    Jim: in the past, max I was able to achieve was 3.5 - 4 (at max. magenta = 170 units). I don't think I had leaks between the lamp and the opening where the filter goes, but it is possible.

    I recently took the Omega F head apart and adjusted everything, top to bottom, left to right, right to left, to make sure there was zero gaps/leaks.

    I also changed the styrofoam liners, just to make quadruple-sure I wasn't losing anything because of a less-than-pure-white mixing chamber.

    Jack Rosa

  5. #5
    RalphLambrecht's Avatar
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    I have no troublegetting anISO grade 5 or more from a Durstdichroic headon Iford or Agfa paper with Dektol1+2and 2-4 min development.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  6. #6

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    If you read Ilford's fact sheet on contrast control, you'll find that Ilford's paper will max out around 4.5 grade with 150M on Omega dicroic heads. As will any other of the Kodak filtration types......

  7. #7
    JackRosa's Avatar
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    Quote Originally Posted by WayneStevenson View Post
    If you read Ilford's fact sheet on contrast control, you'll find that Ilford's paper will max out around 4.5 grade with 150M on Omega dicroic heads. As will any other of the Kodak filtration types......
    JR> Thanks Wayne, I appreciate you taking the time to contribute insight. My personal paper/developer combo is Oriental FB VC and Amidol (1+1). I am not sure the Ilford data would apply.
    Jack Rosa

  8. #8

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    Well, in a way it does apply as it confirms that no your filters are not faded but that the filtration system the Chromegas use has limits with certain papers when used for contrast control.

    Glad to hear that different papers have different sensitivities to the magenta filtration. It never even occurred to me as I just always used Ilford by default and learned to live with the limits when split grade printing with my dicro. Heh.

  9. #9
    JackRosa's Avatar
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    Wayne: I used Ilford FB VC paper (developed in Ilford's paper developer) for a long time and think it is an excellent product. You may want to try Oriental FB VC developed in Formulary's PD-130 diluted 1+1 or Amidol (1+1) … I find the results very appealing.
    Jack Rosa

  10. #10
    David Brown's Avatar
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    Quote Originally Posted by WayneStevenson View Post
    If you read Ilford's fact sheet on contrast control, you'll find that Ilford's paper will max out around 4.5 grade with 150M on Omega dicroic heads. As will any other of the Kodak filtration types......
    Right. I was going to post this, but I'll add that Ilford specifies grade 5 at 199M. Don't know why it's not "200", but that's another issue. There is a lot of thought that a true grade 5 cannot be done with some dicro heads. YMMV

    Even so, you should be able to get a grade 4, if not 4.5. I've never tested my Beseler heads, nor my old Chromega D, since I never print with more than about 50M or I would switch to a condenser enlarger.

    As an aside: I recently purchased the proper blue and green filters, and I plan on doing a little experimenting on the split-grade technique to see if there are any differences between using blue/green and magenta/yellow (using the Ilford 00 and 5). There just might be some differences, but whether they will make any practical difference is another question. FWIW, I only split grade on "difficult" negatives.

    But, I digress ...

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