Dichroic Calibration - Worth It?

Discussion in 'Enlarging' started by bvy, Dec 27, 2012.

  1. bvy

    bvy Subscriber

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    I've been making more prints lately trying to get better contrast -- i.e. the darkest blacks possible without bringing down the highlights. I'm not interested in dodging and burning at this point. The literature suggests that a grade 2 or 3 filter will cover most printing needs, but my results with these always seem to be flat. As such, I find myself using the grade 5 filter more often than not. I thought grade 5 was for slightly more advanced techniques -- like spilt-grade printing -- and not really to be used by itself. Even so, I'm not completely satisfied with my grade 5 prints.

    So I've done some more reading and came across some threads and this link about calibrating your enlarger's color head for variable contrast printing:
    http://www.butzi.net/articles/vcce.htm

    It sounds promising -- I expose for the highlights, and then make adjustments to increase the contrast (blacks) while holding the highlights constant (casually speaking). I have an Omega C760 with dichroic head, but I don't have a light meter or step wedge transparency to run the tests. Before I go down this path and buy "more stuff," I'm wondering if anyone can speak to this process. Does it live up to its promise? Is it worth the effort? I understand the concept and I like the idea, but I want to hear that it holds up in practice and isn't just another academic exercise.

    Thanks.

    (I'm using the Ilford multigrade filters with Ilford MGIV RC paper. I'm using the white light setting of my dichroic enlarger and holding the filters under the lens. My paper developer is Ilford PQ 1:9, 60 seconds.)
     
  2. chriscrawfordphoto

    chriscrawfordphoto Member

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    It would be easier for you to produce negatives that print well on grade 2. Develop them longer and you won't need to use grade 5.
     
  3. michael_r

    michael_r Subscriber

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    Probably only worth doing if you want to figure out exactly which settings to use on your colour head to precisely duplicate the effect of each of your Ilford filters. Not sure I'd bother with that unless your process for exposing and developing negatives was already calibrated to the Ilford filters. Based on the first part of your post, that does not appear to be the case. So if you want to switch from the Ilford filters to using your colour head (yellow and magenta), you can download Ilford's recommended magenta and yellow settings, use them as approximations and go from there.

    http://www.ilfordphoto.com/Webfiles/2010628932591755.pdf


    The problem of insufficient contrast is another matter, and will not be solved by moving to using the colour head. If you find yourself always needing high contrast filters, first do some darkroom tests for things like safelight fog or enlarger light leaks, make sure your filters aren't faded, etc. If everything checks out and your paper and developer are fresh, then you're simply not getting enough contrast in your negatives. Try increasing negative development time. Monitor temperatures. Make sure you are agitating enough etc.

    If you increase the contrast in your negatives you won't need to resort to using high contrast printing filters all the time.
     
    Last edited by a moderator: Dec 27, 2012
  4. cliveh

    cliveh Subscriber

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    I would agree with this post and go further by saying that you should (where possible) produce negatives that require no filtration, given your film development procedure and enlarger type/set up.
     
  5. pentaxuser

    pentaxuser Subscriber

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    Ilford filters give the full range of contrasts without the need to calibrate a dichroic head. Based on what you have said dichroic calibration is not the answer to your problem. Do what Chris Crawford has suggested initially.

    If that doesn't solve your problem then it is even possible that your personal film speed is wrong i.e. it is possible to develop longer and still not have good negs that will give a fine print on grades 2-3. Your exposure based on a correct film speed has to be correct.

    However first things first. Develop for longer and see what does does

    pentaxuser
     
  6. MattKing

    MattKing Subscriber

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    The suggestions above are good. Here are a couple of other things to think about:

    1) it would be prudent to check your enlarger's light source. If, for example, the bulb is wrong or there is some cyan filtration that is not moving out of the way when you use the white light setting, there may be too much green light hitting the paper and therefore reducing the contrast;
    2) light sources with dichroic filters are really nice to use, so if you have one that is working well, you may appreciate the flexibility it offers. You don't really need to calibrate the source, unless you are trying to match previous work. What you need to do is use the Ilford link above to get a reasonable idea of the range, and then become familiar with how it performs, so you can use it reliably in the future. The numbers themselves don't matter, it is the correlation between the settings and how you perceive the results;
    3) it is possible that your desire for high contrast relates mostly to how you see the prints - you may prefer something like the "soot and chalk" look as compared to something with fine tonal gradation. If that is the case, you will need both contrastier negatives and high contrast enlargement filters/settings. I looked at the one enlargement you posted in the APUG gallery and its contrast looks fairly normal. Does it look low in contrast to you?
     
  7. bvy

    bvy Subscriber

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    Thanks everyone. Develop longer as in push a stop? For this session, the negative is Tri-X 400 from my Olympus XA4, developed in D76 1:1 for 9:45. Fresh everything.

    I also use the dialed in filtration, and I have the equivalents from the insert that ships with the paper. (I'm using the Kodak line.) I did some tests a while back and found that the results from the physical filters versus the dialed in filtrations weren't always the same. Maybe my filters are faded (?); anyway, it was a casual test.

    Here are some examples. I like the shadow detail in the top print (grade 2 dialed in) but the blacks aren't very black. The bottom print has blacker blacks and good contrast but the shadow detail is gone.

    img665.jpg
     
  8. cliveh

    cliveh Subscriber

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    Try 12.5 minutes.
     
  9. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    I second Michael's recommendation to check your safelight. Please consider using the Kodak test, and not a "coin test" or its variants. It will only take 10 minutes.

    Unsafe safelight that does not fog paper will reduce contrast and it will force you to use excessively hard contrast filtration, in addition to causing other issues with print-to-print consistency. Second to that would be checking your enlarger for significant light leaks.

    I would say that 4 our 5 darkrooms which I have visited had unsafe safelights. All the other suggestions, which you got, are pretty good too.
     
  10. cliveh

    cliveh Subscriber

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    If you don't have a densitometer, what's wrong with the coin test?
     
  11. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    I don't think you need a densitometer for the Kodak test—the results should be fairly visible across the pre-exposed areas.

    The issue with the coin test is that it does not subject the paper to a pre-exposure under the enlarger. The only exposure the paper gets is the safelight exposure. This way, you are testing the safelight exposure on a sheet of paper that has not crossed the boundary of its inertia. A positive outcome of a coin test is always a positive indication that safelight is not safe, but it will often produce a false negative, in my experience, with safelights that are only slightly unsafe, for example with old safelight filters, some LEDs, and so on. They will not fog the paper, but they will depress contrast just as a pre-exposure of the paper would do, which could be the reason OP is not getting the desired contrast.
     
  12. MattKing

    MattKing Subscriber

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    I expect that Rafal is referring to tests which don't involve a slight pre-exposure of the paper when he mentions a "coin test". You can replace the cardboard in the Kodak test with coins and achieve the same result.

    EDIT: he beat me to it!
     
  13. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    That is exactly what I meant, Matt. Thank you for pointing this out, as I should have made it clearer that I was only concerned about safelight tests that skip that important pre-exposure step, which carries the paper over the threshold.

    PS. Also, the cool part about the Kodak safelight test procedure is that it checks both the pre-exposure before and after the safelight exposure, which can yield different results, contrary to intuition. Whoever came up with the test put a lot of thought into a few simple steps.
     
    Last edited by a moderator: Dec 27, 2012
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  15. michael_r

    michael_r Subscriber

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    You don't need a densitometer. The problem with the standard coin test is it doesn't account for the additive effect of safelight and enlarger exposure. The safelight exposure alone might not visibly fog the paper, but it might bring the paper to it's threshold exposure (the same way flashing does), in which case any further exposure under the enlarger, even very minimal exposure through dense highlights, produces tone on the paper. This decreases local contrast, particularly in the upper mid tones and highlights, and can lead to "muddy" looking highlights, even though the safelight didn't produce enough exposure to visibly fog the paper on it's own.
     
  16. cliveh

    cliveh Subscriber

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    I understand the wisdom of what Rafal refers in terms of the inertia exposure, but as Matt points out this can still be done with any opaque material after initial exposure. However, I understand where Rafel is coming from and respect this point of view.
     
  17. Gerald C Koch

    Gerald C Koch Member

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    Multi-contrast papers are designed to produce a grade 2 or 2.5 without any filtration.. If you cannot then you need to develop longer. The problem seems to be with your processing and not with your enlarger.
     
  18. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    Thank you, Clive, from now on, every time someone asks about safelight tests, I will make sure to be precise in pointing out the matter of the necessary pre-exposure while mentioning a coin test.

    May I just add, that it does make a difference to the outcome of the test when the safelight exposure is made after as opposed to before the enlarger exposure that produces the light tone. The Kodak test takes that into account, but I suppose one could modify a coin test to use two rows of coins and to make two enlarger exposures. It is just that I have never seen a coin test comprehensively include all of those important details, while the Kodak test includes them, and it is concise.
     
  19. cliveh

    cliveh Subscriber

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    Rafal, you make a very good point, as I had not thought about applying the coin test to before and after. Exposure inertia is an important factor that I overlooked. Thanks.
     
  20. bvy

    bvy Subscriber

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    Thanks Matt. It's funny because I was trying to decrease contrast with that print. I printed that one using a grade 1.5 filter for 5 seconds. Same film/paper and development, but a few things are different since I created that print:
    1. Different camera (Yashica T5 there)
    2. Different enlarger (I was using the Omega B600 then -- condenser head)
    3. Same safelight but I actually pointed it up at the ceiling until recently. Now it points down and provides more light.

    About the safelight, it's an old Premier Safelight fitted with Kodak OC filter. I don't have a densitometer, but I'll check out the links and try to run a test.
     
  21. ic-racer

    ic-racer Member

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    Unless you are totally in control of your scene's illumination, you will likely need dodging and burning.

    Don't trust "the literature"

    Increase negative development by 25%

    You thought wrong.

    See above (Increase negative development by 25% and use dodging and burning).


    That is a good technique, but Ilford already did it for you if you use Ilford papers (see the chart they put in with all their paper packaging). Realize what is going on with the 'calibration.' It allows you to change contrast and keep your exposure for middle grays constant. It does not make your final prints look any different, it just saves some steps getting the exposure correct.
     
  22. nworth

    nworth Subscriber

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    The article is excellent, and it gives a good methodology for doing an approximate calibration. Since enlargers vary and dichro filters age, it may be quite worthwhile if you do much printing. An important part of this calibration is the introduction of neutral density to keep exposure times for the various contrast grades approximately the same. Most people just use the Ilford suggestions and go from there. But the Ilford suggestions do not include neutral density, so you have to adjust the exposure for every change in contrast. There are a set of suggestions from Kodak out there that do include neutral density. Many people like to make small adjustments in filtration (usually by changing the magenta) to get the contrast just right, but these small adjustments (up to a third of a grade) usually don't affect exposure that much. Finally, it should be noted that VC papers vary a lot, and a given filtration will not give the same contrast on two different kinds of paper. The differences can be enormous. The calibration technique assumes you print (at least mostly) on one kind of paper. If you switch papers, you can use the grades established for your favorite paper as a point of departure for the new paper, but it probably will not behave in quite the same way. Finally, nothing has been said about the correspondence between density ranges and paper grades. There are some differences between manufacturers here as well, despite some more or less standards. Here is a table from an old Kodak B/W Photographic Papers pamphlet (G-1, 9-71GX):

    Grade Paper Log Exposure Range Negative Density Range
    0 1.40 to 1.70 1.40 or higher
    1 1.15 to 1.40 1.20 to 1.40
    2 0.95 to 1.15 1.00 to 1.20
    3 0.80 to 0.95 0.80 to 1.00
    4 0.65 to 0.80 0.60 to 0.80
    5 0.50 to 0.65 0.60 or lower
     
    Last edited by a moderator: Dec 27, 2012
  23. RalphLambrecht

    RalphLambrecht Subscriber

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    yes, worth it, very much so. you will be able to fine-tune contrast like a master printer. i typically adjust contrst to 1/8gradefor a fine-art pint made for sale. try it and enjoy the power!
     
  24. cliveh

    cliveh Subscriber

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    Perhaps we should just look at the picture to assess it?
     
  25. Bill Burk

    Bill Burk Subscriber

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    bvy,

    You got a lot of good advice, I see nothing to contradict...

    Your shot of the wheel in the garage, it looks like that might be a flat scene in the first place. If you could have known at the time to develop for approximately 12:30 minutes it would have helped this shot. Other scenes, in full sun, may print at Grade 2 with 9:45 minutes of development.

    You develop the print for 1:00 minutes. I used to develop prints for 1:30 minutes, but lately I develop them for 3:00 minutes (Ilford Galerie in Dektol 1:2). Longer print developing will deepen the blacks.

    The safelight test, as has been explained, is better if you print a photograph in the test. Then you see how degraded the highlights become if your safelights are not safe. The Kodak test was a still-life Siamese cat sculpture with polished silver pots and pans. When you see the shine next to the dull thud, it is convincing evidence that a little unsafe light is bad for prints.
     
  26. BMbikerider

    BMbikerider Member

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    As far as I am aware and have seen nothing that disproves it, dichroic filters do not fade! According to the latest times for D76 at 1-1 at 68Deg is the times you are using. Is your camera meter accurate? Is the film speed adjusted right?

    If you are not happy using Ilford Multigrade, change your paper to the Kentmere version. It is made by Ilford after a company buy-out a couple of years ago and it is at least 1 grade harder and at least twice as fast. (Also about 20% cheaper in UK too!) I gave up Ilford MG a long while back because of similar problems to yourself. with no filtration you are supposed to get Grade 2, I estimate comparing it against a non multigrade paper it is about 1 grade softer.
     
    Last edited by a moderator: Dec 28, 2012