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  1. #31
    ic-racer's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    I don't know if anyone has heard of the Gamma-Lambda effect. I did a little research into this sometime ago. Average gradient is affected by the wavelength of light. Blue light tends to decrease the gradient while green tends to increase the film gradient. Red and white light tends to fall somewhere in between. My tests confirmed this. I tested nine films using tri-color filters with my EG&G. Hold times were identical and the film was processed together in a dip & dunk. The differences weren't great but there were differences.

    This is an example from the those tests.

    Attachment 58487
    That effect was not tested here.

  2. #32
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    Stephen;

    I made a post that described the effect of illuminant on film response as a function of wavelength. This is exactly what you describe and is well known in the industry. I did not reference your paper. I was using facts from my own background.

    This is a general problem when one uses a narrow band illuminant to test a film or paper. It gives results that vary as much as you show in your graph or even more.

    This error can lead one quite far astray.

    PE

  3. #33
    Stephen Benskin's Avatar
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    Ron, my snarky response was meant to point out that I was presenting additional information to the discussing and even if it was no more than to re-emphasis a point someone has made previously, I don't feel anyone has the right to discourage discourse.

    As for the issue of the importance of the wavelength of the illuminance, I could agree with you more.

  4. #34
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    Stephen;

    The graph you offer, as I noted above is an excellent emphasis of this point. It is very important, as a picture is worth 1000 words. Right?

    PE

  5. #35
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    Final speed test comparison.

    This graph shows that the measured speed difference between Tri-X and FP4 was about the same percentage (arithmetic speed, not DIN), irrespective of sensitometer's type of light, intensity, color or duration.



    Graph label text "ISO" is to indicate these are percentages of "arithmetic" speed and does not imply the tests were done under strict ISO conditions.
    Last edited by ic-racer; 10-16-2012 at 06:55 PM. Click to view previous post history.

  6. #36
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    I have not used FP4 for many years, but this shows me that I can expose it in my camera with about 45% less exposure than what I have been using for Tri-X and expect to get good results. So, for me that would be an exposure index of 90 based on prior in-camera testing and establishing a personal exposure index of 200 for Tri-X.
    Last edited by ic-racer; 10-16-2012 at 06:52 PM. Click to view previous post history.

  7. #37
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    I tried editing the second graph on post #6 in Photobucket, now the image gives an error when I try to retrieve it. This is a repost of the image. It is very small, so I'll have to re-do the entire graph.

  8. #38

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    So what densitometer should I buy for B&W film testing?

  9. #39
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    Quote Originally Posted by Dismayed View Post
    So what densitometer should I buy for B&W film testing?
    For the two tests mentioned here, it does not matter they all work equally well. I might go for the LED one, but really whatever you can get for less than $100. Even an enlarger will work. These ESECO units list for $750 but we got them for $25 on ebay.

    For "Beyond The Zone System" testing; I don't know. You have to buy into that system and it involves (from what I gather) matching paper to negative with the curves. I'm not a fan of that method of working but that is not to say it is not a good system or that people should not use it. I have used multigrade paper and variable filtration since 1974 and prefer working the negatives up as I print them with trial and error. Also, I don't have the workbooks or software for the system, so I can't test it with these sensitometers.

    If I were to take a guess, I'd say that none of these units will work with that system because some of your photographs will be at exposures longer than 1 second or shorter than 1/1000 second. None of these 4 units duplicates how your film in your camera responds to daylight scenes one might photograph. Again, that is just my guess and someone should test how that system responds to different sensitometers. Of course the reflection densitometers used for reading the paper will be a whole other can of worms. I don't own a reflection densitometer and have turned them down when offered to me for free. I don't think they are very reliable at reading the glossy photographic papers I use. They are designed for the graphic arts industry.
    Last edited by ic-racer; 10-21-2012 at 09:18 PM. Click to view previous post history.

  10. #40

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    Quote Originally Posted by ic-racer View Post
    Of course the reflection densitometers used for reading the paper will be a whole other can of worms. I don't own a reflection densitometer and have turned them down when offered to me for free. I don't think they are very reliable at reading the glossy photographic papers I use. They are designed for the graphic arts industry.
    Actually, a great number of reflection densitometers were made specifically for photo papers. Remember, every processing lab that used standard "process control" methods had to do this for both film AND paper. I can assure you that older machines, at least Macbeth and X-rite, did a fine job on photo paper, glossy or otherwise. I think there is just less need for these things, with respect to a regular photographer (as opposed to a lab operator, or researcher, or the like).

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