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  1. #1

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    Densitometery and Contrast Index (CI)

    As the new owner of a densitometer, attempting to get a better understanding of how it is used to determine the contrast index (CI) of a negative. Can someone point me to a resource that might help explain how the CI is determined or perhaps offer a little Densitometery for Dummies...

    Thanks,
    Mike C

    Rambles

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    Quote Originally Posted by photomc
    As the new owner of a densitometer, attempting to get a better understanding of how it is used to determine the contrast index (CI) of a negative. Can someone point me to a resource that might help explain how the CI is determined or perhaps offer a little Densitometery for Dummies...

    Thanks,
    Hate to sound like a broken record but the best way to figure this out is to read Phil Davis' book "BTZS".

    Calculating CI or Gamma as Kodak or Ilford does it is somewhat involved and requires strict controls. If you are still curious about how they do it you can read Todd and Zakia'a "Photographic Sensitometry." But it is really dry and overkill if all you want is to use the results to better control your process.

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    Not a broken record at all Jorge, guess just need to go ahead and order the BTZS book and read it...sometimes I think the only dense thing around the house is me

    But...even old dogs learn new tricks sometimes. Main thing is not sure I understood what part of a negative is read when I see posts here about negative of 1.6 or 1.7..
    so I would guess that reading the book should help clarify.

    Thanks....BTW, if I could would ship paper and metal to you just to see some new prints....
    Mike C

    Rambles

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    Quote Originally Posted by photomc
    Not a broken record at all Jorge, guess just need to go ahead and order the BTZS book and read it...sometimes I think the only dense thing around the house is me

    But...even old dogs learn new tricks sometimes. Main thing is not sure I understood what part of a negative is read when I see posts here about negative of 1.6 or 1.7..
    so I would guess that reading the book should help clarify.

    Thanks....BTW, if I could would ship paper and metal to you just to see some new prints....
    You are confusing density range (DR) with CI. Contrast Index, to explain it simply is the slope of the straight part of the H&D curve. The trick, and where manufacturers dont agree is what two points to use to determine the slope. So Kodak does it one one, Ilford does it another way, but they are both pretty close.
    Density range is the spread between the shadow with detail and the highlight with detail as read with a densitometer. For example, if your shadow with detail has a value of .45 and your highlight has a value of 1.9 then your density range is 1.45....

    Thanks for the offer Mike, I might take you up on it and have you help me reship paper, ordering straight from B&S is just too expensive and they refuse not to include an invoice which has shipping charges on it. Mexican customs bases their import tax on the price of the item plus the shipping charge.....what a scam!

  5. #5
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    Quote Originally Posted by Jorge
    . . . ordering straight from B&S is just too expensive and they refuse not to include an invoice which has shipping charges on it. Mexican customs bases their import tax on the price of the item plus the shipping charge.....what a scam!
    Sounds like we need to get a couple of cross-border "underground railroads" going. Take Ilford film north to Canada, return with medications. Take alt-process paper south, return with the really good tequila. And here I thought NAFTA was supposed to solve all of that. (ROFLMAO)
    [COLOR=SlateGray]"You can't depend on your eyes if your imagination is out of focus." -Mark Twain[/COLOR]

    Ralph Barker
    Rio Rancho, NM

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    Aww men, dont get me started with NAFTA.....Mexicans really got suckered with that deal.....BTW, medicines are even cheaper here than they are in Canada....

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    As to a trans-border underground railroad, you're just a bit too late. The customs service keeps finding tunnels which go under the border. Unfortunately, there is better money in drugs and humans than in photographic paper and supplies.

    Jorge, what kind of import duties are you paying down there? "Isn't there some way we can resolve this problem?" tim

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    Quote Originally Posted by photomc
    Not a broken record at all Jorge, guess just need to go ahead and order the BTZS book and read it...sometimes I think the only dense thing around the house is me

    But...even old dogs learn new tricks sometimes. Main thing is not sure I understood what part of a negative is read when I see posts here about negative of 1.6 or 1.7..
    so I would guess that reading the book should help clarify.

    Thanks....BTW, if I could would ship paper and metal to you just to see some new prints....
    Glad you asked the question, Mike. I've been having the same problems. I have read that part of the BTZS book, but don't understand all that it says yet. I'll have to keep working on it.
    Diane

    Halak 41

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    ann
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    check with Lee, i sent him some stuff that Richard Knoppow sent to me, it might help.

    You are not the only one tht stuggles with this lol

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    Quote Originally Posted by Jorge
    You are confusing density range (DR) with CI. Contrast Index, to explain it simply is the slope of the straight part of the H&D curve. The trick, and where manufacturers dont agree is what two points to use to determine the slope. So Kodak does it one one, Ilford does it another way, but they are both pretty close.
    Density range is the spread between the shadow with detail and the highlight with detail as read with a densitometer. For example, if your shadow with detail has a value of .45 and your highlight has a value of 1.9 then your density range is 1.45....
    LOL - Not surprised Jorge, am the first to admit that I am confused.
    But then, just spent the past week in a class on object oriented analysis and design (geek speak) - three semester's in a 5 days..whew!

    If I understand what you are saying, is the DR is you take a densitometer reading of the shadows of the negative (my guess would be the one you metered when you determine the exposure), then read the highlights (same as used for the inital metering) and then do the math to find you DR. Right?
    From what I have read, this is also, how you BTZS guys read a scene to get your SBR - Ok, there is more to it than that, but this is part of it - right?

    Quote Originally Posted by Jorge
    Thanks for the offer Mike, I might take you up on it and have you help me reship paper, ordering straight from B&S is just too expensive and they refuse not to include an invoice which has shipping charges on it. Mexican customs bases their import tax on the price of the item plus the shipping charge.....what a scam!
    Not a problem buddy, would be happy to help out any way I can. Buying materials should not be this much a PIA, no matter where you live.

    Quote Originally Posted by colrehogan
    Glad you asked the question, Mike. I've been having the same problems. I have read that part of the BTZS book, but don't understand all that it says yet. I'll have to keep working on it.
    Thanks Diane, it really helps to know I'm not the only one that is confused.
    But with all the good folks here, I know we will get this down and get on to more serious things like shooting/printing and of course hanging these nice new prints on the wall...after all the main reason I am doing this is so that I can put something up I can really be proud of.


    Quote Originally Posted by ann
    check with Lee, i sent him some stuff that Richard Knoppow sent to me, it might help.

    You are not the only one tht stuggles with this lol
    Thanks Ann, will be visiting with Lee at the DR - with densitometer in hand later this morning, your timing is perfect.


    You know if I did not think this was all worth it, I really would not do it...but have seen enough difference in peoples work here before and after they tamed the process that I firmly believe it is worth the effort.

    Thanks to everyone for you input...
    Mike C

    Rambles

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