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  1. #51
    ic-racer's Avatar
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    Do the curves look OK? If you are doing an ASA/ISO test then your numbers are just from two points on the curve, wonder if one of the curves looks funky?

    I have had some curves (done with rotary processing) where the curve takes a sharp spike upward before the 1.3 log H distance, perhaps related to agitation. If the curve looks funny then I don't feel comfortable using the ASA/ISO method.

    Since I spent a couple months of my life making a spreadsheet that calculates the "W" speed, I use that but there are also other methods for specific film-to-film relative speed comparisons.

    I have not tried it yet but it looks like an interesting thing: http://www.freepatentsonline.com/5543883.pdf

    "Furthermore, it is possible using the method of the present invention and a single sensitometer to cross-reference different photographic materials using the same process."


    Even more interesting is the reason I am studying the equation.
    "It is therefore an object of the present invention [equation] to provide a method of calibrating or cross-referencing one sensitometer with another using the characteristic curve for a particular material [film]."

    Basically, using the same type of film and similar processing conditions we all could calibrate our sensitometers to, each other's. As I see it, the equation takes into account variations in both sensitometer light intensity and variations in step-wedges between units.
    Last edited by ic-racer; 07-13-2012 at 11:44 PM. Click to view previous post history.

  2. #52
    Bill Burk's Avatar
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    Quote Originally Posted by Leigh B View Post
    I shoot a step tablet against a neutral gray background, using a camera and a lens.

    I don't take pictures with an enlarger. Why would I test film using one?

    - Leigh
    With a transparent target the range of possible exposure samples is practically unlimited. Not because a typical scene would have it but because you want to see how the film deals with it. You exclude flare, some say that is good.

    With a reflective target you are limited to 1-100% reflection... if you are only taking one shot. You include flare, some say that is good.

    You can take several reflective shots and get practically unlimited exposure samples in-camera by shooting a series of reflective targets at different exposure settings. That's the old classic ZS technique, shoot a gray target placed on Zone 0, I, II... IX, X, XI, etc. Some say that is a flare-free test because there is no bright/dark contrast working against you.

    I've done that, it took about an hour to setup and shoot six sheets of film with the entire sequence. So much work I would be willing to undertake it maybe once every few years. Well I can say I did it once. I may never do it again.

    With an enlarger-based control-strip exposing jig, the time to make a test strip is down to a few seconds.

    Having a jig makes it easy enough to expose the last few frames of an unfinished roll of film or expose a separate sheet and get feedback whether your development results meet your expectations.

    As you can expect, now it is reasonable to perform a family of film curves every year (to get better results because I assume every year I get better in the lab) or when you want to switch developers or try a different film.

  3. #53
    Leigh B's Avatar
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    Yes, the procedure I use is based on the ZS. I have no problem getting a full range of densities this way. It only takes a few exposures.
    This is what happens in the real world, which is also limited to reflectances in the 0% to 100% range.

    I absolutely do not understand this obsession with 'flare'. If you have such a problem, correct it before you do the tests.

    If it takes you an hour to shoot six sheets of film, something is seriously wrong.

    I suppose if you keep changing film and developer, you may need to run tests every year or so.

    I've used Rodinal for over 50 years, and only a couple of different films over that period.
    My results are consistent, and produce exactly the negatives I expect, so why should I repeat the tests?

    - Leigh
    Last edited by Leigh B; 07-13-2012 at 11:45 PM. Click to view previous post history.
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  4. #54
    Bill Burk's Avatar
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    Quote Originally Posted by ic-racer View Post
    Do the curves look OK? If you are doing an ASA/ISO test then your numbers are just from two points on the curve, wonder if one of the curves looks funky?

    I have had some curves (done with rotary processing) where the curve takes a sharp spike upward before the 1.3 log H distance, perhaps related to agitation. If the curve looks funny then I don't feel comfortable using the ASA/ISO method.

    Since I spent a couple months of my life making a spreadsheet that calculates the "W" speed, I use that but there are also other methods for specific film-to-film relative speed comparisons.

    I have not tried it yet but it looks like an interesting thing to do:
    I do not call what I do ASA/ISO because I do not follow every requirement (and I haven't paid for a copy of the standard). For example the D-76 is 3 months old. Small tank, agitation each 30 seconds, 10 minutes development (previously I had hit slightly lower CI at 9 minutes so I added another minute).

    The curves are smooth, straight lines with a nicely tapered toe just as you approach 0.1... There is no detectable fog - I fixed the tail and it measures same as B+F from the developed film. I hit three exposures on the roll of 35mm film and averaged the readings. There was a trend that the last strip (the one on the outermost spiral) had a little more density than the two inner strips. I averaged all three strips. I didn't just get within tolerance +/- 0.05 of the 0.8 rise. I nailed it... within 0.01.

    My speed determining method is simple, I have a graph and a ruler at the top. All my speed determination and CI reading is done by graph. When I feel like I need to move the speed ruler (when I nail the ASA triangle)... I just move it to make it agree with box speed. So now that I nailed a film that used to be ASA 32 as EI 50-64 I am facing a tough call. Do I move the ruler?

  5. #55
    Bill Burk's Avatar
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    Quote Originally Posted by Leigh B View Post
    Yes, the procedure I use is based on the ZS. I have no problem getting a full range of densities this way. It only takes a few exposures.
    This is what happens in the real world, which is also limited to reflectances in the 0% to 100% range.
    Well there's the 0-100% in shadow and another 0-100% in full light. So a real scene has more range than flat copy.

    Quote Originally Posted by Leigh B View Post
    I absolutely do not understand this obsession with 'flare'. If you have such a problem, correct it before you do the tests.
    In practice, flare takes what I spot and place on Zone II up to Zone III. Not a deal breaker but annoying.

    Quote Originally Posted by Leigh B View Post
    If it takes you an hour to shoot six sheets of film, something is seriously wrong.
    I was shooting Minor White's two-tone target, one sheet of film with about a dozen increasing exposures to cover Zone 0 to XIII. Nothing seriously wrong, just a wonderful concentration exercise that teaches the concept of each step double the previous.

    Quote Originally Posted by Leigh B View Post
    I suppose if you keep changing film and developer, you may need to run tests every year or so.

    I've used Rodinal for over 50 years, and only a couple of different films over that period.
    My results are consistent, and produce exactly the negatives I expect, so why should I repeat the tests?

    - Leigh
    I come from a pre-press graphic arts background where running test strips is routine, so perhaps it is a comfort zone for me to throw in a test strip every few runs.

    I'm not all over the place with film. For 4x5 I only shoot TMY-2.

    For roll film, I like slow fine-grain traditional film... Panatomic-X is my favorite... I have experimented with other slow films looking for a replacement.

  6. #56
    Leigh B's Avatar
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    Yes, I know a real scene has more range than flat copy. That's why I use multiple exposures to cover the full range.

    If you have a full stop error due to flare, there's a problem that needs to be corrected.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  7. #57

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    Quote Originally Posted by Bill Burk View Post
    I do not call what I do ASA/ISO because I do not follow every requirement...
    ...
    So now that I nailed a film that used to be ASA 32 as EI 50-64 I am facing a tough call. Do I move the ruler?
    Hi Bill, I don't think you have things nailed down well enough to know anything for sure. (Unless you happen to know the actual power output of the sensitometer.) You can't count on the film response (out of date, right?) or the developer condition, so everything is a moving target.

    The film and developer are what they are, and you should be able to assign a specific EI for them based on a sensitometric test. To me, the main problem is that you really aren't sure (that I know of) that the sensitometer still meets light output specs. Or maybe your attenuators aren't right, if you even have them.

    The best cheap way I can think of for (roughly) checking the sensitometer is to expose sensi wedges on some fresh high-grade C-41 film, such as Kodak Portra, then have it processed in a place you know, where the process is well within spec (this is confirmed by process control charts or data, based on Kodak control strips). Preferably they will also run a process control strip simultaneously with your film. The control strip is really the only feasable way to confirm that the process was right. Then you use the color negative (for still pictures) method to figure the speed. You need a color densitometer (I think it's status M) to measure results. Check on the details, but you need to measure all 3 dye layers and probably average the exposure values.

    If this test confirms the manufacturer's ISO speed, then your sensitometer is probably reasonably close. I think that personally, I'd just use the sensitometer to establish best development times/film response, etc. Then use an actual shooting test to establish the best EI. Good luck!

  8. #58
    ic-racer's Avatar
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    Quote Originally Posted by Bill Burk View Post
    (when I nail the ASA triangle)
    That is what I was curious about, but if you have nice curves that is of course a great method.

    In terms of that Pan-X you have, the neat thing about exposure determination for pictorial subjects is that the gold standard is always right out your window! If you make some pictures with the Pan-X exposed so many stops less than TMY based on your sensitometer results, are the prints acceptable? As you know the speed methods are all traceable back to Jone's et al 'panel of observers' rating prints.

    In fact most of my sentitometric data concerns finding out what exposure and development worked for negatives that are known to print well. Subsequent sensiometric testing of 'unknown' films saves me from having to make a bunch of prints and get an opinion form my wife on which pictures looks better...
    Last edited by ic-racer; 07-14-2012 at 06:59 AM. Click to view previous post history.

  9. #59
    ic-racer's Avatar
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    I also think that one of home sensitometeric testing's most important roles is to share information over the internet between the remaining wet darkrooms out there.

    A world-wide forum like this is truly a miracle in human communication; too bad it is frequently used just to quibble over opinions and preferences..."you can't have Yellow as a favorite color because..." or "you can't like the 'New Topographics' because..." or "your method of producing outstanding prints is faulty because..." etc.

  10. #60
    Photo Engineer's Avatar
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    Bill;

    The release test for films used D76 straight and not 1:1 IIRC. That is one difference.

    The second is that these films are daylight balanced and the speeds are measured with a given light temperature. Any deviation from that temperature will affect speed.

    Just some thoughts for you to consider while wandering in the ASA triangle.

    PE



 

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