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  1. #11
    tih
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    Calibrating RH Designs Analyser Pro for a Meopta color head.

    Enlarger: Meopta Opemus 6 with a Color 3 head.
    Paper: Ilford Multigrade IV RC, glossy.
    Developer: Ilford Multigrade, concentrate diluted 1+9, 60s at 20C.

    Target: to determine filter settings and calibration data that fully
    utilize the available contrast range, with ideally spaced grades, a
    reasonable trade-off between added ND (Y+M) in the middle of the scale
    and added exposure time at the ends, and zones VIII½ and I½ at the
    ends of the grey scale on the analyser (i.e. zones VIII and II at the
    next to last diodes on either end).

    Tools: Stouffer TP4x5-31 transmission step wedge and R2110 reflection
    guide (as recommended in "Way Beyond Monochrome"), and RZ9 zone system
    chart.

    First, I determined the paper's response to the Meopta filters. I
    contact printed the step wedge at 40 filter unit intervals from 200M
    to 200Y, evaluated the densities of all steps on each using the
    reflection guide, and made graphs of the results. From each of these
    characteristic curves I could calculate the ISO grade resulting from
    the use of that filter setting, using the density range from relative
    0.09 to 0.9Dmax, as suggested in the book. A derived graph was made,
    showing this relationship. This turned out quite smooth and not far
    from linear for much of the range, although the graph levels off a
    little bit at the extreme range of yellow filtering, and much more so
    for magenta -- there is some increase in hardness to be gained beyond
    120M, but not very much. My results also show that I'm able to
    squeeze a range of grades out of this set-up that is very close to the
    standard ISO range: I can't quite reach the softness of ISO 00, while
    at the other end, 200M gives me a bit more contrast than ISO 5.

    Next, I calculated the ideal exposure range of each half grade, from
    00 to 5, where the ratio between successive pairs of grades is equal,
    as for the ISO standard grades. Thus, my target grades are all a tiny
    bit harder than the ISO ones, but are correctly spaced, and give me
    the optimum utilization of the available range. These numbers were
    entered into the Analyser.

    I then estimated the needed filter settings, based on my graphs, with
    added neutral density (i.e. overlapping Y and M filtering) taken from
    Ilford's suggested filter settings. Since I'd previously done a
    calibration using Ilford's suggestions, I interpolated initial offsets
    to enter into the Analyser based on that experience.

    Finally, three rounds of calibration and adjustment of filter settings
    and exposure offsets, the first with 1/6th step test strips, the
    subsequent two with 1/12th, allowed me to tweak everything to the
    point where I now hit my idealized grades to within the limits given
    by the imperfect repeatability of filter settings, the 1/12th step
    resolution, and my own limited ability to evaluate the exact densities
    at the dark end of the range by visual comparisons. Along the way,
    the contrast settings in the Analyser were corrected slightly, but as
    a set; they are still properly spaced.

    Here's the resulting data set:

    Grade: 00 00½ 0 1 2 3 4 5
    Magenta: 0 0 0 5 10 25 50 50 55 65 80 110 200
    Yellow: 200 140 110 85 65 50 40 30 20 10 0 0 0
    Offset: 11 5 -1 -4 -8 -19 -21
    Contrast: 172 140 114 93 75 61 50


    Since I also use Ilford's warm tone version of this paper from time to
    time, I've gone through the process of calibrating the Analyser for
    that paper, using the same filter settings as shown above. (I could
    have used separate filter settings especially tailored to this paper,
    but the differences would have been very small.) My settings for MG
    IV RC warm tone glossy and the above filtering are as follows:

    Grade: 00 0 1 2 3 4 5
    Offset: 29 22 14 11 7 -5 -9
    Contrast: 199 161 129 102 85 72 62


    I'm quite happy with my results, although a little bit disappointed
    that Ilford's own developer for their MG IV paper doesn't give me
    quite as deep blacks as I'd like to see. Increasing development time
    doesn't help in this regard, so I plan to experiment with toning
    (probably selenium?) to enrich the blacks without lowering the high
    tones. Improved longevity of the print will be a bonus. :-)

  2. #12
    andrew.roos's Avatar
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    Hi tih

    Thanks for an impressive set of scientific testing on our behalf! I have a couple of questions in order to be able to make the most of your results.

    1) Are these designed to provide equal exposures for different grades? Is any exposure compensation required for the highest and lowest grades, where one of the filters is set to 0 so there is no ND effect?

    2) Possibly a related question: what is the meaning of the "offset" figures you provide?

    3) Do you know offhand whether these same values will work with the Meochrom 2 head of the Opemus Va enlarger?

    Many thanks
    Andrew

  3. #13
    tih
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    Andrew,

    the "offset" and "contrast" numbers are for the Analyser Pro, so they
    won't be useful unless you have one. And no, again because I let the
    Analyser control the exposure time for me, these numbers will not give
    equal exposure times at different grades. You'd have to dial in more
    ND in the middle of the scale to achieve that. The amount I've got
    there is just to smooth it out a bit.

    When I'm next in the darkroom, I'll check how much the Analyser Pro
    actually changes the exposure time when I switch between these
    settings, and post the result.

    -tih

  4. #14
    andrew.roos's Avatar
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    Thanks tih!

    And thanks Maarten for your post #9, which I just saw now. I will try out the two-filter values with my Meochrom II head.
    Last edited by andrew.roos; 03-19-2012 at 06:08 AM. Click to view previous post history.

  5. #15
    maarten m's Avatar
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    pretty impressive study, tih!
    i'm interested what ND settings you need to keep a constant exposure though.

    mm

  6. #16
    tih
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    OK, I've checked what the Analyser Pro does with my data, now. When I change grades, it corrects the exposure so that the highlights in the print stay the same, and the darker areas change their value. Thus, the change in exposure time is what's needed to keep the toe of the curve, where the paper just departs from pure white, in the same place, while letting the shadows burn out to black on the paper when contrast is increased. To achieve that, here's what it does with the exposure times for my filter settings:

    Grade: 00 00½ 0 1 2 3 4 5
    Magenta: 0 0 0 5 10 25 50 50 55 65 80 110 200
    Yellow: 200 140 110 85 65 50 40 30 20 10 0 0 0
    Multiplier: 1.95 1.72 1.52 1.35 1.20 1.13 1.06 1.00 1.00 1.13 1.27 1.52 1.84

    The multiplier shows how much the required exposure time increases to keep the highlights in the final print at the same near-white level, compared to the grade 2½ exposure.

    Now, based on this, it should be possible to create an estimate of how much ND (equal amounts of M and Y) to add in order to get the same exposure time throughout - but it might also be that someone who doesn't use the Analyser Pro would like a more central zone to stay constant with varying grades, and it's not impossible that my filter settings actually do something quite close to that with no correction of exposure. Perhaps someone with a Meopta color head would like to give it a shot, and let us know what happens?

    I'm pretty sure that these filter settings squeeze the maximum contrast range out of Ilford MG4 paper, with even spacing along the ISO contrast scale, so they should be a really good starting point.

    -tih

  7. #17
    tih
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    It just struck me: it's easy to correct the exposure by adding real ND filtration in the Color 3 head. The scale there is: 30 units equals 1 step. So, let's just use the exposure correction calculated by the Analyser Pro, and convert those to Meopta ND filter values. This gives us the following:

    Grade: 00 00½ 0 1 2 3 4 5
    Magenta: 0 0 0 5 10 25 50 50 55 65 80 110 200
    Yellow: 200 140 110 85 65 50 40 30 20 10 0 0 0
    ND: 0 10 15 20 25 25 25 30 30 25 20 10 0

    Once you've found an exposure time, at one of these settings, that places the highlights correctly, you can change settings by following the table, and use the same exposure time, and you'll change the contrast of the print while keeping those highlight details in the same zone.

    Note: I haven't actually tested this. It would be cool if someone did.

    -tih
    Last edited by tih; 03-31-2012 at 09:06 AM. Click to view previous post history. Reason: The ND filter scale is linear, of course, not exponential.

  8. #18
    tih
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    OK, I was a bit confused. Of course the ND scale is exponential, as I first thought. So here's the table again, this time with (rounded) correction amounts in 1/3 and 1/2 aperture steps, and on the Meopta ND filter scale:

    Grade: 00 00½ 0 1 2 3 4 5
    Magenta: 0 0 0 5 10 25 50 50 55 65 80 110 200
    Yellow: 200 140 110 85 65 50 40 30 20 10 0 0 0
    Open by: 1 1 ½ ½ 0 0 0 0 0 0 ½ ½ 1
    or by: 1 2/3 2/3 1/3 1/3 0 0 0 0 0 1/3 2/3 1
    or add ND: 0 5 10 15 20 25 25 30 30 25 20 10 0

    -tih

  9. #19
    maarten m's Avatar
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    thanks, tih!
    so this should keep the highlights in place en shift the darks down.
    i'll try that out next tim i go into the dark ...

  10. #20
    maarten m's Avatar
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    one more question: you say the ND-scale is exponential.
    does this mean that a 10pt shift does not exactly accord to 1/3 stop
    but is different whether it's from 5 to 15 or from 45 to 55?
    i'm getting a bit confused here ...

    mm

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