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  1. #11
    Bill Burk's Avatar
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    You can turn down the flash if you like.

    I've tried to find out the meter-candle-seconds of my EG&G but here on APUG, we haven't concluded exactly what I've got. So I don't know the math. In my case I believe that the No. 96 ND filter is a little "yellow" so "sensitometrically" I am getting more density than I calculated. Especially in blue light which film is most sensitive.

    This is why I recommend a physical neutral filter. IC-Racer can show you pictures of what I mean, he has cut some out of acrylic.

    But you don't need the accuracy of illumination to get results that are good enough for process control testing.

    The goal is easy: You want to expose enough but not too much. You want to reduce the light output to the point that the graph drops down near zero (above B+F) in the toe. In case you cannot reduce the light that much, it's OK if your lowest toe reading falls around 0.10 (above B+F).

    To repeat my earlier post, if the flashmeter indicates f/1.0 at ISO 100 - you are pretty close to what you need.

  2. #12

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    The "ready" light comes on in electronic flashes when the capacitor is about 1/2 or 2/3'rds charged. Furthermore, the maximum voltage applied to the capacitor depends on how charged your batteries are; i.e., the voltage of the supply. So for consistency, I suggest (1) waiting at least one minute after the "ready" light lights up, and (2) powering the unit from AC instead of batteries.

    Mark Overton

  3. #13
    Bill Burk's Avatar
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    Quote Originally Posted by albada View Post
    The "ready" light comes on in electronic flashes when the capacitor is about 1/2 or 2/3'rds charged.
    Good advice. With the variable power manual flash setting, if it's well-designed, you probably won't use all the charge per flash.

    For process control purposes... I'd keep the flashmeter handy and test the flash output several times just before you get the film out to test. Do this a few times until you are confident in the flash output stability. Write down what you got (or the average).

    Then do the flash for film test... Later, if something doesn't come out right, you'll have a record of how much flash output you were getting.

    If your light consistency falters, even by a stop, you can still get an idea what your contrast index is for any specific development run.

    Once you setup the "system," it should be so easy to use that you can run a test shot in with every few batches of film you develop -- just to keep tabs on your contrast index (verify that you get what you aimed for).

  4. #14
    polyglot's Avatar
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    Quote Originally Posted by albada View Post
    The "ready" light comes on in electronic flashes when the capacitor is about 1/2 or 2/3'rds charged. Furthermore, the maximum voltage applied to the capacitor depends on how charged your batteries are; i.e., the voltage of the supply. So for consistency, I suggest (1) waiting at least one minute after the "ready" light lights up, and (2) powering the unit from AC instead of batteries.
    Meh. If I measure the output of any of my flashes (Minolta 5600 and Bowens 1000DX), they are consistent shot-to-shot within the 1/10 stop resolution of my flash meter, which is IMHO quite good enough when you're testing against a wedge with 1/2 stop resolution. I'd expect any high-quality thyristor flash to be as good as mine.

  5. #15
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    that is what i do. because according to my lightmeter my strobes are within 1/10stopfrom flash to flash. i spotmeter for the center bars of the stouffer 45and ,and take it from therethe stouffer is taped to a thick milky piece of neutral plastic, and this approach has worked for years, just need to seal against the flash to avoid flare. go for it.
    Regards

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

  6. #16
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by RalphLambrecht View Post
    that is what i do. because according to my lightmeter my strobes are within 1/10stopfrom flash to flash. i spotmeter for the center bars of the stouffer 45and ,and take it from therethe stouffer is taped to a thick milky piece of neutral plastic, and this approach has worked for years, just need to seal against the flash to avoid flare. go for it.
    Ralph, are you contacting the Stouffer to the film? That would be my intention, following the issues I encountered doing the WBM tests, described on another thread. You mentioned that you seal against the flash to avoid flare—are you using a camera or a duplicator? I am not sure why significant flare would occur when contacting. Many thanks.
    Last edited by Rafal Lukawiecki; 09-18-2012 at 07:39 AM. Click to view previous post history.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  7. #17
    RalphLambrecht's Avatar
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    Quote Originally Posted by Rafal Lukawiecki View Post
    Ralph, are you contacting the Stouffer to the film? That would be my intention, following the issues I encountered doing the WBM tests, described on another thread. You mentioned that you seal against the flash to avoid flare—are you using a camera or a duplicator? I am not sure why significant flare would occur when contacting. Many thanks.
    i'm using a self-made slide duplicator, flash from one side and photograph from the other.then, i cover the duplicator with a black cloth to make sue i have no light leaks when photographing into the flash so to speak. i have a picture of the set up somewhere.
    Regards

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

  8. #18

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    Quote Originally Posted by Rafal Lukawiecki View Post
    Unfortunately, my flash meter, L-508, only shows f stop value, there is no readout in lux-sec.
    Make a reading at your box with the flat diffuser. Count the number of stop from f/1.0 for example if it displays 5.6 3 then 5.6 is 5 stops from f/1.0 plus .3 then it's 5.3
    The Lux.second is (2^5.3)*2.5=98 lux.sec

  9. #19
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by Chan Tran View Post
    Make a reading at your box with the flat diffuser. Count the number of stop from f/1.0 for example if it displays 5.6 3 then 5.6 is 5 stops from f/1.0 plus .3 then it's 5.3
    The Lux.second is (2^5.3)*2.5=98 lux.sec
    Thank you! I was looking for the formula, I'm glad it is so simple.

    On another note, I have been testing the repeatability of my flash with a meter, which shows down to 0.1 of an f/stop. It seems to depend on the selected power output. At lower outputs, it is less precise, hitting up to +/- 0.2 f/stop third of the time. At a higher output it is much more accurate, hitting the same level 5 out of 6 times, and deviating -0.1 once in six.

    I wonder if a tungsten bulb controlled by a spare enlarger timer would be still a better choice in the long term, but perhaps I have what I need to complete the re-test now.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  10. #20
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    Quote Originally Posted by Rafal Lukawiecki View Post
    I wonder if a tungsten bulb controlled by a spare enlarger timer would be still a better choice in the long term, but perhaps I have what I need to complete the re-test now.
    The exposure time is generally either too long or too difficult to control exactly. So you either run into reciprocity failure of the film (exposures >1s) or you have inaccuracies due to warmup/cooldown (different intensity and redder spectrum, both of which will have film-dependent effects on sensitivity) of the bulb consuming a significant fraction of the exposure duration (< 0.5s). A very bright tungsten bulb (bright enough that a 0.25s exposure is enough to do your sensitometry) with a mechanical shutter should be a very usable combination though.

    Tungsten bulbs also have a redder spectrum than daylight, to which film is less sensitive (in a very film- and source-dependent manner) so then you have to correct for that somehow. Strobes are a much neater and more-controllable solution.

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