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  1. #11
    Bill Burk's Avatar
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    Thanks ic-racer,

    I believe this shows all the sensitometers you tried are usable for process control. It's better agreement than I expected.

    The choice of sensitometer makes a difference in the 2nd decimal place of accuracy.

    But if you want to process to a consistent, predictable contrast... Any of these tools will do the trick.

  2. #12
    Photo Engineer's Avatar
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    Note that the exposure with the EG&G gives higher speed due to its being "white" light where the LED types are not truly white. Therefore, part of the energy is missing which leads to slower results.

    The LED sensitometers are good but will give you what amounts to slower speed.

    PE

  3. #13
    ic-racer's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    Note that the exposure with the EG&G gives higher speed due to its being "white" light where the LED types are not truly white. Therefore, part of the energy is missing which leads to slower results.

    The LED sensitometers are good but will give you what amounts to slower speed.

    PE
    Thanks for viewing the thread.

    Don't read anything in to x-axis variables on those graphs. The x values are just "numbers" or "units" not Lux-seconds. The sensitometers all have different intensities and exposure times and I'd consider the relative right-left position of each curve on the x-axis in the graphs to be random. This was not a film speed test. (That is to come, stay tuned!)
    Last edited by ic-racer; 10-14-2012 at 04:44 PM. Click to view previous post history.

  4. #14
    Rafal Lukawiecki's Avatar
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    Do you have a similar, prior experience with a Kodak Process Control Sensitometer? I'm not familiar with any of those, but looking for one.
    Last edited by Rafal Lukawiecki; 10-14-2012 at 06:40 PM. Click to view previous post history. Reason: Corrected Name
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  5. #15
    Photo Engineer's Avatar
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    Quote Originally Posted by ic-racer View Post
    Thanks for viewing the thread.

    Don't read anything in to x-axis variables on those graphs. The x values are just "numbers" or "units" not Lux-seconds. The sensitometers all have different intensities and exposure times and I'd consider the relative right-left position of each curve on the x-axis in the graphs to be random. This was not a film speed test. (That is to come, stay tuned!)
    I fully recognize that the intensity of these instruments may be far different. I should have made that post of mine conditional in that respect. Sorry.

    If you have any degree of congruence in intensity at one selected wavelength or group of wavelengths, then if the speeds differ in the exposed films, then the spectral output of the group of instruments varies.

    Since we see that here, then either the absolute intensity of each device varies or the spectral output varies.

    PE

  6. #16
    ic-racer's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    I fully recognize that the intensity of these instruments may be far different. I should have made that post of mine conditional in that respect. Sorry.

    If you have any degree of congruence in intensity at one selected wavelength or group of wavelengths, then if the speeds differ in the exposed films, then the spectral output of the group of instruments varies.

    Since we see that here, then either the absolute intensity of each device varies or the spectral output varies.

    PE
    Relative speed will be tested within each sensitometer. So, if sensitometer "A" shows 2 stops between two films and sensitometer "B" also shows two stops between those same two films then the response of the two sensitometers will be deemed OK for home darkroom film speed comparisons.

    I know a few posters have shown some interest in absolute sensitometer calibration, but only about 5 of us here care about that, and I'm not going to address that. For everyone else, they just need to know how much faster or slower some oddball film from another continent is, compared to their favorite film that was just discontinued.

    Ideally we'd test a number of films with different spectral responses, but lets see how just two films compare. It could be that the two films response to the LED units are so different that further testing is not needed. If the first test is close, I can keep going with other films.
    Last edited by ic-racer; 10-14-2012 at 09:47 PM. Click to view previous post history.

  7. #17
    ic-racer's Avatar
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    Quote Originally Posted by Rafal Lukawiecki View Post
    Do you have a similar, prior experience with a Kodak Process Control Sensitometer? I'm not familiar with any of those, but looking for one.
    I have no experience, but I'd be surprised if it behaved any different than the others in the first test.

  8. #18
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    I have a lot of information on the construction and method of operation of each of these three units. I'll post more about them when all the results are in. Having said that, I do want to say that the ESECO unit is by far the most sophisticated of the bunch. It actually has photoreceptors in the light chamber that monitor the LED intensity and correct the time based on the intensity. That takes care of any warm up and decay issues with the LEDS. It also addresses any LED intensity changes as the battery ages. As a practical note, the ESECO prints a much nicer step wedge on the film (compared to a Stouffer wedge). The numbers are clearer and it is much easier to align the test patches with the densitometer aperture and still see the wedge number.

  9. #19
    Bill Burk's Avatar
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    ic-racer,

    Not to put you to more work, but can you do a quick Reciprocity study using the EG&G at different exposure times?

    I think it would be valuable to show how different the gradient might be from a home-made "flash" sensitometer used at low light output (for example time might be 1/10,000 second at lowest setting).

    I'd do the test but I don't have the acetate filters to balance the different speeds, and I think you made a set...

  10. #20
    ic-racer's Avatar
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    Quote Originally Posted by Bill Burk View Post
    ic-racer,

    Not to put you to more work, but can you do a quick Reciprocity study using the EG&G at different exposure times?

    I think it would be valuable to show how different the gradient might be from a home-made "flash" sensitometer used at low light output (for example time might be 1/10,000 second at lowest setting).

    I'd do the test but I don't have the acetate filters to balance the different speeds, and I think you made a set...
    Should be easy to do. I think it will turn out OK. The Wejex in the test had an exposure time of 1 sec and the EG&G was set to 1/1000. There was not detectable difference in the way the exposed film responded to development time changes between those two. So, I suspect 1/10,000 would be similar.

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