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  1. #71
    markbarendt's Avatar
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    Ilford's data on Delta 3200 shows an ISO if 1000.

    http://www.ilfordphoto.com/Webfiles/201071394723115.pdf

    For Kodak this was copied from tech pub f32

    EXPOSURE
    KODAK T-MAX P3200 Professional Film is specially designed to be used as a multi-speed film. The speed you use depends on your application; make tests to determine the appropriate speed.
    The nominal speed is EI 1000 when the film is processed in KODAK T-MAX Developer or KODAK T-MAX RS Developer and Replenisher, or EI 800 when it is processed in other Kodak black-and-white developers. It was determined in a manner published in ISO standards. For ease in calculating exposure and for consistency with the commonly used scale of film-speed numbers, the nominal speed has been rounded to EI 800.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  2. #72
    AndreasT's Avatar
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    Everybody I know in my small world exposes these film at 3200. None of them have ever read the data sheets

  3. #73
    markbarendt's Avatar
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    Quote Originally Posted by AndreasT View Post
    Everybody I know in my small world exposes these film at 3200. None of them have ever read the data sheets
    Sadly, I agree that ignorance of reality is the norm.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  4. #74
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    Sadly, I agree that ignorance of reality is the norm.
    And we should struggle to correct that, not make excuses for its continuation.

  5. #75
    markbarendt's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    And we should struggle to correct that, not make excuses for its continuation.
    Absolutely!
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  6. #76

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    Agree 100%. In fact, in additon to the specific tech publications/instructions for specific materials, both Kodak and Ilford have a variety of very good papers available on their websites about testing, process control, negative contrast, printing etc. I often direct people to these in threads but Ilford and Kodak usually get drowned out!

    Actually given a few other recent threads I'm thinking of posting a thread with links to all these documents. They are excellent resources for people starting out.

  7. #77
    Stephen Benskin's Avatar
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    Quote Originally Posted by AndreasT View Post
    Basically I use a similar method used by Phil Davis in exposing film under an enlarger. Develop five or more testa at differnt times and plot them. I use a more contrasty "standard" to Phil Davis since I find his reults to soft to be practical.
    Davis' BTZS is the closest method to good sensitometry, but it's still a method and while I've never found anything in Davis' book to be inaccurate, he has a tendency to short hand the explanations of some point especially theory. It's been awhile since I've read BTZS, but I believe he mentions how testing with an enlarge doesn't produce an accurate film speed. The color temperature of the lightsource, the lack of precision of most timers, and the difficulty in determining the illuminance of the light source are all contributing factors. The enlarger is a compromise. Isn't it better to know that than to think the results can be as accurate as with a sensitometer?

    It also relates to how the manufacturer gets this ISO rating and what it means. As I understand it and I may be wrong here but the rating correlates to a contrast of 1,5 am i wrong here? or me that is an overcast day in winter. Not a sunny day when many people take their cameras and run on the streets.
    The 1.5 you are thinking about is the log-H range used to determine the average gradient when doing fractional gradient testing. How it relates to how the manufacturer gets the ISO rating is what I'm talking about. By knowing how the details, parameters, and theory on a test, the photographer can better utilize the testing data. There will be a slight difference in the film's responce when testing under an overcast day and sunny day. the ISO speed standard uses daylight color temperature for exposure. When the speed standard changed the color temperature for the film exposure from sunlight to daylight they had to adjust the speed constant from 1.0 to 0.80. But if the photographer is testing using natural light, they are probably using a camera. All the variables associated with camera exposures will tend to obscure and speed change caused by different color temperatures.

    The value of 0.62 for contrast index that you said was standard in most books, I believe came from the contrast parameters defined in the ISO speed standard. The delta 1.30 log-H by delta 0.80 density has a gradient between 0.61 and 0.62; however, it can't be referred to as a contrast index because the use of that term implies a testing methodology. The 1.30 log-H range is intended to define the shadow portion of the curve and not the average gradient.

    Now, a CI 0.62 is perfectly acceptable as a normal. It's just a little high to be considered the results from the statistical average conditions. Most books have aims more around 0.56 and 0.58 depending on the average flare factor - whether it's for a large format lens or medium and 35 mm lens.

    My basic premise is that there is good testing and bad testing. The best possible decissions come from a position of knowledge.
    Last edited by Stephen Benskin; 01-17-2013 at 05:51 PM. Click to view previous post history.

  8. #78
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    I see what you are getting at Stephen, or most of it. I use a enlarger to expose my film but I put in a lens with a shutter so that the times I would suppose is relativly accurate. While there is a strong talk about accuracy here I believe if one is pretty close the parameters should cancel each other out on average.
    Though there may be problems here and there or even false results, by seeing the collected data one does get a knowledge or feeling how ones methods work. This will get us what we want.
    I feel comfortable when I test my materials.

  9. #79
    Bill Burk's Avatar
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    AndreasT,

    I think you don't have misconceptions.

    When you expose a test strip, even if you set aside the whole concept of speed, you can always get a measure of the contrast.

    Photographers could work from box speed, if they used appropriate metering technique (like incident metering). But people meter badly at times. I remember times when I got underexposed shots using the camera on automatic because I included too much sky or backlit situations.

  10. #80
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    All I know now is that I have become confused. I am going to have read up on all this. I feel like I am in a dark forest at night.



 

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