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  1. #71

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    Quote Originally Posted by Ornello
    Yes, but...how does one expose the film so precisely? Using a camera won't work, because of flare, etc. You have to use process control strips....
    Or you can make your own - use a step wedge that has been calibrated and you enlarger. Correct the enlarger to daylight, and then you can measure the exposure with your incident light meter with a flat diffuser (spot could be used, but incident is more direct). Use the look-up table that came with your incident meter to convert incident readings to lux, multiply by exposure time (shoot for 0.4 to 1.0 seconds) and then figure out the exposure of each step on the test neg from the known densities of the step wedge. This will give exposure values in lux-seconds, which I see Kodak uses in their charts.

    Davis covers much of this in the BTZS book (although slightly differently).

    Or, pick up an EG&G sensitometer. I have a friend with one. They show up on eBay occasionally.

    Kirk - www.keyesphoto.com

  2. #72
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    Quote Originally Posted by Claire Senft
    The only reason I believed that a special protracter was necessary was due to Phil Davis's statements in the fourth edition of the BTZS book. It really doesn't matter to me since I find average gradient completely suitable for my needs but much appreciated was the helpful advice that you gave me and the friendly spirit in which it was given.

    How goes the oboe playing?
    My first born son is getting a degree in music from Virginia Wesleyan in May and I am going to join him in his senior piano recital. We will do a movement of the Poulenc oboe sonata. I am furiously making reeds that will allow me to recapture what I once had. It's like trying to get another picture like the one you thought was your masterpiece. Magic reeds don't do it any better than magic paper or film.

    I must have stayed up too late last night. You don't use log-log paper to plot the H&D curve, as you are plotting density against log exposure when you use either the step number or the actual density of a step density wedge.

    As to flare, there are various opinions. You can get a flare-free curve and make some kind of a theoretical correction when you go to use the data in practice, or you can photograph a reflection wedge with the camera you plan to use and find out how flare affects your CI. A lot depends on whether you are doing it for your own use or are planning to pass the data on to others.
    Gadget Gainer

  3. #73

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    Good For You Patrck

    The session with you son sounds as if it will be a very nice event for both of you. Knock their socks off Pat! Geez from reed making to rocket science, you have had some experiences.

    I have the graph paper that I need. I am more than satified in using average gradient. I was interested in finding out if those that were so certain that blank film had a CI thought that a developed film with a single density on it was any use from a practical standpoint. If you read thru the thread from the beginning, as you may alredy have done, you will see that it was not a pretty conversation with a hostility being involved.

  4. #74

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    Quote Originally Posted by gainer
    As to flare, there are various opinions. You can get a flare-free curve and make some kind of a theoretical correction when you go to use the data in practice, or you can photograph a reflection wedge with the camera you plan to use and find out how flare affects your CI. A lot depends on whether you are doing it for your own use or are planning to pass the data on to others.
    Davis in Beyond the Zone System describes a method for testing for flare and applying the data in field use in diverse SBR scenes. And in WinPlotter there is a data entry that allows one to compensate the curve for the value of flare indicated.

    Assuming that you use a very efficient lens hood, a compendium bellows for example, the amount of flare is fairly low with modern lenses in low and medium contrast scenes, say SBR 5, 6 and 7, but can be quite high with SBRs of 9 and higher.

    Sandy

  5. #75

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    You guys probably aren't interested in hearing this, but Stephen Benskin has done some programming that does some really nice tone reproduction graphs - here's a sample of a 2 quadrant graph that he posted on photo.net last year.

    http://www.photo.net/bboard/big-imag...ad_id=17658784

    He can plug in differing levels of flare, as well as different H&D curves for the film. When a 4 quatrand curve is made, you can see how the exposure at the lens is modified as it is recorded on the film, is then transferred to the paper, and then that is compared to the original scene. I find it really interesting.

  6. #76

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    Quote Originally Posted by Kirk Keyes
    You guys probably aren't interested in hearing this, but Stephen Benskin has done some programming that does some really nice tone reproduction graphs - here's a sample of a 2 quadrant graph that he posted on photo.net last year.

    http://www.photo.net/bboard/big-imag...ad_id=17658784

    He can plug in differing levels of flare, as well as different H&D curves for the film. When a 4 quatrand curve is made, you can see how the exposure at the lens is modified as it is recorded on the film, is then transferred to the paper, and then that is compared to the original scene. I find it really interesting.
    The sample graphs you reference appear to be similar to the ones in Stephen Benskin's article on flare in the Jan/Feb issue of Photo Techniques. I read the article when it first came out but the subject was only of peripheral interest to me since it is focused primarily on the problem of flare with the Zone System, while I use primarily BTZS. However, the article appears to be conceptually sound, and is well researched and written.

    The issue of flare itself, whether for Zone System of BTZS application, is an important one, so why not start a new thread on the subject if you like. I would suggest not continuing the discussion in this thread, if for no other reason the fact that the oxymoron "CI of Blank Film" is not an appropriate title for such discussion.

    Sandy
    Last edited by sanking; 04-11-2005 at 08:01 PM. Click to view previous post history.

  7. #77

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    Quote Originally Posted by sanking
    The sample graphs you reference appear to be similar to the ones in Stephen Benskin's article on flare in the Jan/Feb issue of Photo Techniques. I read the article when it first came out but the subject was only of peripheral interest to me since it is focused primarily on the problem of flare with the Zone System, while I use primarily BTZS. However, the article appear to be conceptually sound, and is well researched and written.

    The issue of flare itself, whether for Zone System of BTZS application, is an important one, so why not start a new thread on the subject if you like. I would suggest not continuing the discussion in this thread, if for no other reason the fact that the oxymoron "CI with blank film" is not an appropriate title for such discussion.

    Sandy
    Sandy - Yes, the graphs are similar. I posted the link since some others brought up flare. But Stephen can make some really cool graphs that convey a lot of info that most of us are not used to seeing in a graphical form.

    Actually, I really have no pressing conceptual questions or examples I wish to submit to the unhuddled masses on flare at this moment, so I guess I have to pass on your suggestion. But yes, the affects of flare on exposure is an interesting subject and one that is very often glossed over due to a lack of understanding of the principles behind it, and probably more importantly, lack of hard numbers with which to work. If there is some aspect about it you have been pondering, I would be interested hearing about it in a new thread as well.

    Kirk

  8. #78

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    Quote Originally Posted by sanking
    ... if for no other reason the fact that the oxymoron "CI with blank film" is not an appropriate title for such discussion.

    Sandy
    Please note that the thread was about "CI of Blank Film", not "CI with blank film".

    AS I said before, you cannot derive CI with only blank film, but I was discussing an intrinsic property of a piece of developed film.

    Kirk

  9. #79

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    I will start the thread

    Mr. King, I am also interested in this topic because it seems to me to be the least controllable aspect of the BTZS techniques...and other systems of exposure and development.

    Damned good Idea Sandy.

  10. #80

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    Quote Originally Posted by Kirk Keyes
    Please note that the thread was about "CI of Blank Film", not "CI with blank film".


    Kirk
    OK, I edited the message to read "CI of Blank Film."

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