Contrast Achieved with Dichroic Filters

Discussion in 'Darkroom Equipment' started by JackRosa, Feb 12, 2014.

  1. JackRosa

    JackRosa Member

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    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??
     
  2. ic-racer

    ic-racer Member

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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 a moderator: Feb 12, 2014
  3. Jim Noel

    Jim Noel Member

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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.
     
  4. JackRosa

    JackRosa Member

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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.

    :blink:
     
  5. RalphLambrecht

    RalphLambrecht Member

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    I have no troublegetting anISO grade 5 or more from a Durstdichroic head:wink:on Iford or Agfa paper with Dektol1+2and 2-4 min development.
     
  6. WayneStevenson

    WayneStevenson Member

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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. JackRosa

    JackRosa Member

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    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.
     
  8. WayneStevenson

    WayneStevenson Member

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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. JackRosa

    JackRosa Member

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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.
     
  10. David Brown

    David Brown Subscriber

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    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 ... :whistling:
     
  11. WayneStevenson

    WayneStevenson Member

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    "There is a lot of thought that a true grade 5 cannot be done with some dicro heads."

    I have found I can't. At least as I said, with Ilford papers. Though I did go over that document the other day (I only read it some time ago to figure out filtration). It does mention that the reason is that the filtration in dichroic heads are meant for the sensitivity of colour papers. Not B&W VC. Which in terms of Ilford's sensitivity to yellow or magenta, make sense.
     
  12. WayneStevenson

    WayneStevenson Member

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    Oh, and interested to hear your experience with the filters vs. dichro split filtering. I only tried split filtering with dichro myself. And through a standardized workflow, I tend to split filter pretty much every negative to get a consistency in my body of work that I print in the darkroom.
     
  13. JackRosa

    JackRosa Member

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    Split Grade: Dichroic vs. Filters

    I have tried split-grade printing using both methods: under-the-lens filters and dichroic filtration (max. 170 Yellow & 170 magenta with my enlarger). It has been a while and my memory fails me, but I seem to remember I liked the results a little better with the filters. However, I find it more convenient to use dichroic filtration (turn of a knob vs. handling filters, especially when I'm using the 300mm enlarging lens).

    I concluded that, unless the negative required that I used the under-the-lens filters, I would try using dichroic filtration instead.
     
  14. WayneStevenson

    WayneStevenson Member

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    I find it much more convenient myself as well. Guilty pleasure. :wink: