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  1. #41
    ic-racer's Avatar
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    I calibrate mine with name-brand film (of course this is a 'quick and dirty' calibration). But think about it, film is cheap and available and has extremely hight quality control for it's light sensitivity. And, with respect to speed, all I really want to know anyway "is this new film/developer combo faster or slower than Tri-X in D76 processed to a .7 gamma"

    Also, I don't post my H&D curves with the calibrated axes.
    Last edited by ic-racer; 03-26-2010 at 09:46 PM. Click to view previous post history.

  2. #42
    ic-racer's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    With the 10-3 compensator, the exposure for 10-2 was 20.3mcs. I then used ND filters to adjust for the different film speeds. I used .6 NDs. They brought the exposures down to 4.78mcs for 100 speed films, 1.18mcs for 400 speed films, and 0.28mcs for TMZ and Delta 3200.
    I have also done that mis-matching of the compensators to help fit the film range to the wedge with the limited ND filters I have.

    I really like the concept of those compensators. They will be almost as stable throughout time (unless the plexiglass yellows or something) as a carbon filter, at an order of magnitude less in production cost.

  3. #43
    ic-racer's Avatar
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    Here is the Wejex sensitometer I wrote about earlier in the thread. I did not have a digi camera when I had it apart, so no pictures to post. But it is night-and-day different inside compared to the EG&G:


  4. #44
    Stephen Benskin's Avatar
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    Quote Originally Posted by ic-racer View Post
    I really like the concept of those compensators. They will be almost as stable throughout time (unless the plexiglass yellows or something) as a carbon filter, at an order of magnitude less in production cost.
    The compensators are on film or acetate. The lines are clear but not cut outs. Mine haven't yellowed yet.

    Greg Davis: This is the most accurate method of getting the characteristic curve of your film or paper.
    The idea is to make it knowable, repeatable, and produce the smallest number of variables. That way you are confident the results reflect what you are testing for. Contacting eliminates flare. Optical conditions can be integrated into the interpretation of the data later. The color temperature of the light source represents daylight balance, and the repeatable exposures guarantees that any difference you see in density between samples is the result of the processing or film and not the exposure. If you are using film samples from the same batch, then you know you are testing mostly for the processing. A calibrated step tablet guarantees knowable densities. Most commercial densitometers are accurate to +-0.01 or +-0.02. The possible degree of error with combining the variance in the confirmation of the densities of the step tablet and the variance in the reading of the resulting film densities can be fairly large. A calibrated step tablet eliminates one of the variances. If I know the amount of light falling on the step tablet and the density of the different steps, I am able to know the about of light striking the film at each of the steps. This allows for actual log-H values instead of relative log-H and speed is calculated using actual log-H.

    Interestingly, the EG&G sensitometer isn't acceptable for use in ISO testing. The standard requires a "non-intermittent illuminance-scale type". EG&G uses a flash unit. It appears that one person's accurate is another's not-so-much.

    Steve

  5. #45
    ic-racer's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    The compensators are on film or acetate. The lines are clear but not cut outs. Mine haven't yellowed yet.
    Ok, I see. Mine did not come with any, so I made them based on the [poor] pictures in the manual. Mine did come with one clear plexiglass plate with a black painted border, so I figured the others would also have been clear plexiglass with black paint.

    I'll have to post some pictures of my home-made filters. I used trial and error to scrape lines in the paint until I had a similar 'speed' from the film at each of the 3 settings. I know that is not the way they were supposed to be calibrated. The original filters were calibrated to intensity, and small differneces in film speed were then ascribed to high-speed reciprocity failure.

  6. #46

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    [QUOTE=ic-racer;969940]Here is the Wejex sensitometer I wrote about earlier in the thread. I did not have a digi camera when I had it apart, so no pictures to post. But it is night-and-day different inside compared to the EG&G:


    In addition to a Mark VII I also have a Wejex. The basic exposure of the Wejex is about 2.5 seconds and you must adjust with ND filters. If I were calibrating film for long time exposures the Wejex would be a better choice than the EG&G.

    Stephen, how did you make the mcs readings with your EG&G?

    Sandy King

  7. #47
    Bill Burk's Avatar
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    This is a good discussion for me because I have to make (or buy) line filters or ND filters for the EG&G that Steve sold me.
    Seems to me a good test would be to flash same piece of film twice (work and turn) at the same (10-2) setting - one with and one without the line filter that I'm making. Then the displacement of the curves between "with" and "without" would be the density of the filter. I could scritch away until I hit a reasonable whole log value.

  8. #48
    Stephen Benskin's Avatar
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    [QUOTE=sanking;970188]
    Quote Originally Posted by ic-racer View Post
    Stephen, how did you make the mcs readings with your EG&G?
    I just find the transmitted light using

    Transmittance = transmitted light / incident light

    Transmittance is the reciprocal of Opacity and Opacity is the antilog of Density. I find the step tablet density that I want to find the mcs for and calculate the Transmittance of that density and plug it into

    transmitted light = Transmittance * incident light

    Fortunately, I've incorporated it into my program so I don't have to do the calculations by hand every time.

    Or you were wondering how I got the initial values for the different settings. That was done by EG&G. I sent them the NDs too so they could do the tests with them. I figured there would be some light loss from reflection and absorption within and between the filters. I also make sure that the filters are stacked in the same order each time I test to assure consistency.

    As a side note, those using sensitometers should also take the hold time for latent image keeping into consideration. All the accuracy and repeatability of the sensitometer would be worthless without a consistent hold time.

    Bill,

    That idea strikes me as brilliant.

    Steve
    Last edited by Stephen Benskin; 03-27-2010 at 01:54 PM. Click to view previous post history.

  9. #49

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    Quote Originally Posted by Stephen Benskin View Post
    Interestingly, the EG&G sensitometer isn't acceptable for use in ISO testing. The standard requires a "non-intermittent illuminance-scale type". EG&G uses a flash unit. It appears that one person's accurate is another's not-so-much.

    Steve
    Interesting.

    And by extension the EG&G sensitometer would not be useful in film testing where exposures get into the reciprocity failure range.

    Sandy King

  10. #50
    Stephen Benskin's Avatar
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    Quote Originally Posted by sanking View Post
    Interesting.

    And by extension the EG&G sensitometer would not be useful in film testing where exposures get into the reciprocity failure range.
    Actually, I think that's the one area it has the advantage over the other types. The Mark VII has two settings that appear to be practical only for short exposure reciprocity testing.

    This is only a guess, but I believe the reason why intermittent sensitometers aren't preferred is partly because of short exposure reciprocity failure. I also think it's because of the inconsistency of the light over the period of discharge. You know, build up and fall off from peak intensity and any possible shifts through color temperature as that happens. I remember reading something about having the non-intermittent light source on for a few minutes before testing so that the color temperature and intensity fluctuations equal out. The timing device for the exposure for this type of sensitometer is a rotating pie wedge.

    Steve



 

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