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  1. #11
    Nicholas Lindan's Avatar
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    Quote Originally Posted by Krzys View Post
    If I find the exposure time for a print at grade 2 and then want to increase the contrast grade will I then have to increase the exposure time as well?
    If you are using Ilford paper and Ilford filters then you can change contrast with the same time. Obviously, only one shade of grey will remain constant in tone.

    MGIV FB WT #2 -> #3 1/2 will keep a 0.9 OD grey (a bit lighter than ZIV)
    MGIV FB #00 -> #3 1/2 will keep an 0.45 OD grey (ZVI, skin)
    MGIV RC #00 -> # 31/2 will keep an 0.55 OD grey (ZV - ZVI, 18% - skin)

    For other tones you can find the correction from the paper speed charts published by Darkroom Automation http://www.darkroomautomation.com/support/index.htm

    The charts give the paper speed - that is the amount of exposure in stops - for each grade of paper and each zone-system tone.

    For example, with MGIV RC you want to change from #2 to #3 contrast, keeping the shadows (ZIII) the same:

    • For #2 the speed for ZIII is 8.36
    • For #3 the speed for ZIII is 7.89
    • The difference is -.47, or -1/2 a stop
    • If you reduce the exposure 1/2 a stop (divide by 1.4) then ZIII will stay constant as you go from grade #2 to #3.


    Second example, with MGIV RC you want to change from #2 to #1 contrast, keeping the light highlights (ZVIII) the same:
    • For #2 the speed for ZVIII is 5.38
    • For #1 the speed for ZVIII is 5.24
    • The difference is -.14, or -1/8 a stop
    • If you reduce the exposure 1/8 a stop (divide by 1.1) then ZVIII will stay constant as you go from grade #2 to #1.


    The stops table http://www.darkroomautomation.com/su...stopstable.pdf will help with adjustments to time if you aren't using an f-stop timer.

    However, if you are using a color head your filtration and time settings may not match Ilford's filters. A good place to start is with Ilford's suggestions for filtration for 'constant time' printing. If you want to calibrate your system a good approach, if you don't want to use a step tablet, is to make a zone grey scale for each of the contrast grades you use most often http://www.darkroomautomation.com/support/zonestrp.htm
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  2. #12
    Greg Davis's Avatar
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    I don't remember where I read it, but when using a color head with B&W paper, increasing or decreasing the yellow has no change on the time, but the magenta requires a 0.1 second increase for every point added. Try it and see if your results are in line with this.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  3. #13
    Ian Grant's Avatar
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    Quote Originally Posted by Greg Davis View Post
    I don't remember where I read it, but when using a color head with B&W paper, increasing or decreasing the yellow has no change on the time, but the magenta requires a 0.1 second increase for every point added. Try it and see if your results are in line with this.
    It's not as simple as that

    But close to the mark.

    I use a single filter setting, and I fly by instinct, I dial in a bit of extra Magenta, or go Yellow -quite rarely when needed and can guestimate the exposure difference quite accurately.

    But that's years of printing experience, reading other peoples poorly exposed negatives

    Ian

  4. #14
    RalphLambrecht's Avatar
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    Quote Originally Posted by Krzys View Post
    If I find the exposure time for a print at grade 2 and then want to increase the contrast grade will I then have to increase the exposure time as well?
    Krzys

    Take a look at:

    http://www.darkroomagic.com/DarkroomMagic/Darkroom.html

    and scroll down to 'Paper Exposure Compensation'. I hope it's self-explanatory.

    In addition, I recommend:

    http://www.waybeyondmonochrome.com/W...largersEd2.pdf
    Regards

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

  5. #15
    Greg Davis's Avatar
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    Quote Originally Posted by Ian Grant View Post
    It's not as simple as that

    But close to the mark.

    I use a single filter setting, and I fly by instinct, I dial in a bit of extra Magenta, or go Yellow -quite rarely when needed and can guestimate the exposure difference quite accurately.

    But that's years of printing experience, reading other peoples poorly exposed negatives

    Ian
    As I said, I just read it somewhere, but it does give you somewhere to start.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

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