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  1. #1

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    clibrating dichroic colour heads for variable contrast black and white printing

    Hello all, came across this at www.butzi.net Is there a quicker way to match the filters (constant exposure when changing contrast grade) given by the paper manufacturer to your own enlarger? Paul Butzi's graph is a neat idea as it gives you a quick visual reference. I use a Durst ac707 autocolour and wish to calibrate it to Ilford VC papers, any comments appreciated.

  2. #2
    clogz's Avatar
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    I use dual filtration (Y+M) as per instructions that come with the box of paper. Time is constant for grades 0-3, 4 and 5 double time (roughly). See also: www.ilford.com
    Digital is best taken with a grain of silver.

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    This is one area that was a struggle for me. Originally, the Ilford instructions specified dichroic filtration from only *one* source, either magenta or yellow. I tried that, with disappointing results. Next, Ilford brought out "Dual Filtration" recommendations, using both magenta and yellow filtration. Using either, I had been comparing prints made with the dichro filtration to those made with the Ilford MG gelatin filters... and in every case the prints made using MG filtration were superior.

    During this, I noticed that Ilford has a #2, #2 1/2, #3, filter -- and none appeared to be "neutral" - one assumes a #2, or 2 1/2 contrast grade *without* filter - apparently that just wasn't so.

    Next, I placed the Ilford MG filters in the enlarger, and using my ColorStar 3000, proceeded to determine just what dichro filtration would be necessary to duplicate the light modified by the Ilford MG filters. Hah!! Not too close to the Ilford (or Kodak) recommendations... which figures - the sources in the various enlargers vary in color temperature; the light from a 211 incandescent enlarging lamp is not the same temperature as the light from the halogen in the Omega D5500 - and I'm sure that is not the same as a "cold" light source.

    Using that data, I am more than satisfied with VC papers.

    This seems to be like most everything else in this game - the manufacturers suggest, and it is up to each of us to wring things out (e.g. film speed and developer) and fine tune for ourselves.
    Carpe erratum!!

    Ed Sukach, FFP.

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    Ed Sukach's Avatar
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    Quote Originally Posted by bogeyes
    Hello all, came across this at www.butzi.net
    Interesting article ... but I was wondering ... do all these meters read in raw "stops" or f/stop settings? The difference between a reading of f/11 and f/12 is not one stop.. ?
    Carpe erratum!!

    Ed Sukach, FFP.

  5. #5
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    Quote Originally Posted by bogeyes
    Hello all, came across this at www.butzi.net Is there a quicker way to match the filters (constant exposure when changing contrast grade) given by the paper manufacturer to your own enlarger? Paul Butzi's graph is a neat idea as it gives you a quick visual reference. I use a Durst ac707 autocolour and wish to calibrate it to Ilford VC papers, any comments appreciated.
    I don't know if it's quicker, but the method described in Way Beyond Monochrome ISBN 0-86343-354-5 is certainly the best.

    G.
    Last edited by argentic; 11-04-2004 at 04:00 AM. Click to view previous post history.
    Wilbert
    http://www.photovergne.com
    Cours photo en Auvergne

  6. #6
    Ed Sukach's Avatar
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    Quote Originally Posted by Ed Sukach
    Interesting article ... but I was wondering ... do all these meters read in raw "stops" or f/stop settings? The difference between a reading of f/11 and f/12 is not one stop.. ?
    Ooops!! I was faked out by the article comparing the accuracy of Zone IV (? was that the number ?) modified digital spot meters... and whether or not the modifications were worth the cost..
    My bad.

    The article on calibrating Dichroic light sources seems accurate enough, although rather involved. What I did was quite a bit simpler ... noting that the Ilford MG filters produced good results, all I did was to emulate their effect.

    I've now read the *right *article... and I'm taking some time to "digest" it. In the future, when I have more time, I'll give it a shot.
    Carpe erratum!!

    Ed Sukach, FFP.

  7. #7

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    Ed, that is the crux, we all need more time thats why I,m looking for a shortcut. good luck, bogy

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    It doesn't take that long to do. Give it a try, it's not that bad! Gilbert's right about _Way Beyond Monochrome_. It's an excellent book. However, if I remember correctly, it's favored approach requires a reflection densitometer. I've used Paul's approach, and it works very well. Since I recently acquired a reflection densitometer, I'll have to give Ralph's (Way Beyond Monochrome) procedure a try. It'll be interesting to compare results.

    Btw., calibrating my contrast grades has lead to the biggest improvement to my printing that I can remember. I find it more valuable, even, than F-stop printing, although that's great as well.

  9. #9
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    Do you own a relection densitometer? If you do, I will share my method with you (it requires a densitometer)
    Jack Rosa

  10. #10

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    If you could find the CC equivalents for the Ilford filters, then you could match the values with your dichroic head. In theory, at least for my Omega C760, the 0-200 values on the dials are supposed to be CC values.



 

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