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  1. #21
    gainer's Avatar
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    If the step wedge densities were truly neutral it wouldn't make any difference. When you measure density, you measure the light incident on the wedge and the light transmitted by it and get the log of the ratio. When you use that same wedge to expose film or paper, the color of the exposing light will make a difference. The exposed and developed film may or may not be neutral gray. It certainly will not be neutral if it was developed in a staining developer. This copy of the step wedge will look different to paper than a neutral density copy would. If the purpose of reading the neg with a densitometer is to predict how a print of it will look, the densitometer should have the same spectral response as the paper. The spectral response of VC paper varies with the spectrum to which it is exposed.

    If that is the purpose, test strips are better that a densitometer for determining the printable density range of a pyro neg on any kind of paper.
    Gadget Gainer

  2. #22
    Helen B's Avatar
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    "If the step wedge densities were truly neutral it wouldn't make any difference."

    If... the question of which mode to use would not arise. It appears from Sandy's measurements that some step wedges are not truly neutral. However, I agree with you that they should be neutral.

    Best,
    Helen

  3. #23

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    Quote Originally Posted by Helen B
    "If the step wedge densities were truly neutral it wouldn't make any difference."

    If... the question of which mode to use would not arise. It appears from Sandy's measurements that some step wedges are not truly neutral. However, I agree with you that they should be neutral.

    Best,
    Helen
    But they are not. I have quite a number of step wedges and every one of these has some kind of actinic filtration that results in a lower maximum density in UV mode than in Visual or Blue.

    Sandy

  4. #24

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    Quote Originally Posted by Helen B
    "If the step wedge densities were truly neutral it wouldn't make any difference."

    If... the question of which mode to use would not arise. It appears from Sandy's measurements that some step wedges are not truly neutral. However, I agree with you that they should be neutral.

    Best,
    Helen
    The acetate base exhibits some UV absorption, in my densitometer the readings are uniformly higher by about 0.09 units.

    IMO, one should use the readings that the film "sees", given that panchromatic film is more affected by visible spectra, I use the readings from the visible channel (blue light) when taking readings from the step tablet. I have not seen any difference in using either readings, since using the UV readings means the curve is shifted 1/3 of a stop to the right. If one is to take readings from stained negatives to "fit" to a given paper curve, then IMO one should read with the channel that the paper "sees" and fit the spectra so that the readings from the densitometer are equal to the spectra to which the paper is sensitive. For example, pt/pd actinic response is in the 290 nm range, my densitometer reads in the 390 range, this means my densitometer is less "sensitive" than the paper so I have adjusted the exposures of my negative to give 1/3 more exposure since my densitometer is reading 1/3 less density than what the paper "sees".

    It has worked for me. YMMV.

  5. #25
    Helen B's Avatar
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    Jorge,

    I'm glad that at least one person agrees with me!

    I've also noticed that the base adds a uniform level of difference between the UV and visual readings (UV density being higher than visual, as Jorge's readings) - but this does not, of course, alter the relative exposure values. So in the case where the UV and visual relative densities (relative step to step) are the same, it should not matter whether UV or visual is used - the curve is just shifted along the x-axis. (I couldn't think of a concise enough way to describe this 'relatively neutral' aspect of base plus silver when I wrote my previous posts, so lazily used 'neutral'.)

    In that case (the UV and visual densities of the step wedge being uniformly different) it would not matter which mode was used unless the densitometer was out of calibration. Then it may be better to measure the step wedge in the mode in which you were going to measure the film density because then the calibration error would partially cancel - the curve would be stretched or compressed diagonally, but would maintain the same general shape. Note that the error would not be cancelled entirely.

    So, if your UV and visual density step wedge measurements are different by a non-constant value there is either something wrong with your densitometer or the density steps in your step wedge are not neutral. It is acceptable for the base not to be neutral, as long as it is uniform.

    The preferable way to avoid errors caused by the possible non-neutrality of the step wedge is to have a calibrated densitometer, and to measure the step wedge in the mode that most closely resembles the way the film will be exposed (usually visual) then to measure the image of the step wedge on film in the mode that most closely resembles the way in which the paper (or next stage in the process) will be exposed.

    How does that sound?

    Best,
    Helen

  6. #26

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    Quote Originally Posted by Helen B
    Jorge,

    I'm glad that at least one person agrees with me!

    I've also noticed that the base adds a uniform level of difference between the UV and visual readings (UV density being higher than visual, as Jorge's readings) - but this does not, of course, alter the relative exposure values. So in the case where the UV and visual relative densities (relative step to step) are the same, it should not matter whether UV or visual is used - the curve is just shifted along the x-axis. (I couldn't think of a concise enough way to describe this 'relatively neutral' aspect of base plus silver when I wrote my previous posts, so lazily used 'neutral'.)

    In that case (the UV and visual densities of the step wedge being uniformly different) it would not matter which mode was used unless the densitometer was out of calibration. Then it may be better to measure the step wedge in the mode in which you were going to measure the film density because then the calibration error would partially cancel - the curve would be stretched or compressed diagonally, but would maintain the same general shape. Note that the error would not be cancelled entirely.

    So, if your UV and visual density step wedge measurements are different by a non-constant value there is either something wrong with your densitometer or the density steps in your step wedge are not neutral. It is acceptable for the base not to be neutral, as long as it is uniform.

    The preferable way to avoid errors caused by the possible non-neutrality of the step wedge is to have a calibrated densitometer, and to measure the step wedge in the mode that most closely resembles the way the film will be exposed (usually visual) then to measure the image of the step wedge on film in the mode that most closely resembles the way in which the paper (or next stage in the process) will be exposed.

    How does that sound?

    Best,
    Helen
    Yep, sounds good to me, agree with all you say here....

  7. #27

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    Quote Originally Posted by Helen B
    Jorge,


    The preferable way to avoid errors caused by the possible non-neutrality of the step wedge is to have a calibrated densitometer, and to measure the step wedge in the mode that most closely resembles the way the film will be exposed (usually visual) then to measure the image of the step wedge on film in the mode that most closely resembles the way in which the paper (or next stage in the process) will be exposed.

    How does that sound?

    Best,
    Helen
    Helen,

    I still believe that if the step wedge has different readings in UV and Visual mode it is the UV readings that should be plugged into the WinPlotter program if that is the mode that is used to measure the densities of the second generation step wedges. And my reasoning continues to be that if you use the Visual reading densities the log density units will be of unequal length in the graphing on the x and y axis.

    And there is more than the logic. When I actually tested the same film test using both values the result was exactly what I had anticipated and predicted. So there is no question but that the actual values used make a difference in plotting. Your question as to which results are right is a valid one, but I find it very compelling when a logical principle is tested and the results validate the premise.

    I have posted a message about this to the btzs forum to see if Phil Davis will comment on the question. If there is a fault in my reasoning I am sure he will identify it.

    Best,

    Sandy

  8. #28
    Helen B's Avatar
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    Thanks Sandy. I'll be interested to hear his reply.

    Regards,
    Helen

  9. #29

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    This has been a very interesting thread..Thanks to everyone. One thought occurred to me is it possible that the step-wedge is coated or incorporates some type of UV filter to protect the steps from fading? This would make some sense, because over time would UV light not cause a change in the step-wedge?

    Since I do not own a step wedge (on the list of things I need to get) and not a practitioner of BTZ, I could be off base...just wondering though. It would explain the results reported I think.
    Mike C

    Rambles

  10. #30

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    Quote Originally Posted by Helen B
    Thanks Sandy. I'll be interested to hear his reply.

    Regards,
    Helen
    Helen,

    You can see Phil's response at www.btzs.org. Go to Forums, then Plotter, and then to Phil's answer to my question.


    Sandy

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