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  1. #11
    gainer's Avatar
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    Quote Originally Posted by Deckled Edge
    How about using a different piece of hardware for densitometry--a scanner? I have not done anything like formal testing, but I use SilverFast software when scanning prints. If you use the straight line algorithm when scanning, with no manipulation, you should get an accurate representation of your print. SilverFast SE 6.0.2 has a densitometer. I have played with this, and it seems useful. Does anyone have experience using a scanner to formally analyze your dried-down prints?
    I have done this with limited success. The response of the scanner is not logarithmic if you read the values as they show on screen. It is possibly, but not essentially, that it is a linear scale. You can test that by scanning a reflection step wedge and plotting the values on semilog paper or by plotting the logarithms of the values on linear paper. If you are lucky the result will be a straight line. You will see that the readings are integers, so the resolution of density will get poorer toward the shadow end of the step wedge.

    The numbers I get from any of several programs including the Photoshop LE range from 0 to 256, which is only 8 bit precision. This is sufficient at the upper end but pretty poor in the shadows.
    Gadget Gainer

  2. #12
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    Quote Originally Posted by Deckled Edge
    How about using a different piece of hardware for densitometry--a scanner?
    [...]
    Yep --- I've read a few accounts of folks using a scanner to do what I want to do. I'd just rather not have to start a project on a computer every time I want to read a print density.

    Although I also want to measure dynamic range on finished prints, the specific thing that got me started on this is that I'm trying to get into a mode where I replenish my developer tray rather than dump it each day -- especially when I have several days in a row where I print. The thought of dumping developer that's still got a lot of capacity left, said developer being one of the major costs of a printing session, was starting to be a disincentive to doing a short print session.

    I switched from a powder-based (Dektol) to a liquid concentrate (Ilford MG IV) developer, then filled up a 4x5 sheet film box with pre-exposed contact prints of a 21-step test wedge. I keep the first of these "test strips" developed in that chemistry as a benchmark, then at the end of each session, I cover the developer and fixer by setting a sheet of freezer paper on top, keeping most of the air out.

    At the beginning of each session, I test the fixer with Hypo check and do a film clearing test, and I process one of my canned test strips. As the developer begins to get exhausted, the set of dissernable steps starts shifting to the left. At that point, I'll add 10-20 ml of and run another strip to get the scale back to the benchmark. (I use big 16x20 cement mixing tubs instead of trays, and use about 3L of solution in the developer and fix tray, and 4L of solution in my cheap-as-dirt single-use citric acid stop tray).

    Right now, I'm just visually comparing the strips, but I'd like to get to the point where I can get the gamma from each one, plot trends and have a real controllable process. Yeah, I'm trying to reproduce what I used to do with roll film processors when I was in the Navy.

    -KwM-

  3. #13

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    I see what you are saying--256 is 2 to the 8th. Therefore, the difference between Zone 8 and Zone 9 is 128, but the difference between Zone 1 and Zone 2 is only 2. On the other hand, this gives a reproducible, recordable number, while the analog meters have many more variables (and, while they are set up logarithmetically, they suffer most inaccuracies at the near and far ends of the scale).
    Question: Did you buy or make your reflectance step wedge? We are all familiar with the Kodak transmission wedges. I think mine is half-toned and would be of limited usefulness, even scanned as a transparency, in this setting.

  4. #14
    lee
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    maybe kevin you might like me to come up and bring my densitometer? I have a little portable job that if you are not using a staining developer will make your life easier. This is only for film as it is a transmission only unit it is an X-Rite.



    lee\c
    Last edited by lee; 11-30-2004 at 01:16 PM. Click to view previous post history. Reason: add info

  5. #15
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    Quote Originally Posted by lee
    maybe kevin you might like me to come up and bring my densitometer? I have a little portable job that if you are not using a staining developer will make your life easier. This is only for film as it is a transmission only unit it is an X-Rite.

    lee\c
    Hey Lee,

    Wonderful offer & I might take you up on it when I get around to doing curves on film. Right now, though, I'm focused on trying to find the best way to read my step wedge contact prints.

    Thanks very much,

    -KwM-

  6. #16

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    Quote Originally Posted by kwmullet
    Hey Lee,

    Wonderful offer & I might take you up on it when I get around to doing curves on film. Right now, though, I'm focused on trying to find the best way to read my step wedge contact prints.

    Thanks very much,

    -KwM-

    If you want reflection density readings, I will read them for you. IM me off post if you are interested.

  7. #17
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    Quote Originally Posted by Donald Miller
    If you want reflection density readings, I will read them for you. IM me off post if you are interested.
    Thanks Donald, but my project right now for reflection densitometry is to read test strip prints I make before each printing session as a guide for how much I should replenish my developer tray.

    So far, the most workable thing I've heard is the suggestion to scan it. Once I pull my test strip print from the fix and give it a quick hot wash, I can dry it in 40 seconds in my microwave and scan it on my scanner. I was resisting the idea of pulling a computer into my process for anything but music and reading APUG during dead time, but it's beginning to sound like scanning is my best option. I realize the accuracy won't be all that great, but for the purposes of doing process QC, the scans need only be consistent with each other, not with any kind of real-world benchmark.

    (side issue -- how does one actually measure drydown? Surely, people aren't putting wet prints on their densitometer. Is it strictly by eyeball?)

    Besides, I'd end up doing my control charts in excel anyway.

    Later on, I'll get a real densitometer to do real sensitometry. After several visits to eBay, I'm drawing the conclusion that two cheap/old single-purpose (one transmission and one reflection) densitometers would probably be cheaper than one dual-mode densitometer.

    cheers,

    -KwM-

  8. #18

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    Quote Originally Posted by kwmullet
    John,

    Great article recommendation. I'll certainly go through it in more detail when measuring negs, but in this particular instance, I'm looking for a way to do REFLECTION densitometry of a print, not TRANSMISSION densitometry of a negative.

    -KwM-
    KwM - that article has all the info in it you need to do this. But instead of backlighting a negative to get transmission values, front-light your control strip prints and then read them. This will give you the data you need to calculate reflection densities.

    And for what you are trying to do, you don;t need to worry about a fancy bracket to hold the meter. Just using your hand-held meter will get you there. A close-up filter may be nice, to get the focus right, but if your print areas are large enough, that may not be necessary either. As to flare, you can block out extraneous light from your subject and meter to minimize that too.

    Kirk - www.keyesphoto.com

  9. #19
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    Quote Originally Posted by kwmullet
    Later on, I'll get a real densitometer to do real sensitometry. After several visits to eBay, I'm drawing the conclusion that two cheap/old single-purpose (one transmission and one reflection) densitometers would probably be cheaper than one dual-mode densitometer.

    cheers,

    -KwM-
    I bought my Gretag reflection densitometer for $ 40,- on a photo fair. And with a little patience you can find one that cheap on Ebay. I wonder now why I put up with my BTZS modified spotmeter-densitometer for so long.
    Wilbert
    http://www.photovergne.com
    Cours photo en Auvergne

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