Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,982   Posts: 1,523,850   Online: 1007
      
Page 8 of 12 FirstFirst ... 23456789101112 LastLast
Results 71 to 80 of 120
  1. #71
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    Quote Originally Posted by cao
    Forgive me if I seem dense, but what is the correction preserving? Without even considering the developer, we could think in terms of density of development sites for a given light in a given time. Are we preserving zone V? How is this site density curve being changed? What I am shooting at is this; I have the niggling feeling that the curve is changed in a way that isn't fully correctable by changing development. If this is the case, then we can stretch tones around by deliberatly exposing so as to create RF, and hence RF can be used as a creative control with the right films. I'm seeking a correction function mapping an site density curve to a different curve in the face of RF. Do we already know this from Gainer's correction?
    The failure of film to obey our elegant law of reciprocity has been known for a long time. The general effect is to change film speed with length of exposure. It is often thought of as having a threshold below which there is complete reciprocity. That is, we can exchange light for time. Less light needs more time in a reciprocal inverse manner. Actually, the failure is there from 0 time on up, but is negligible below a certain exposure time.

    It is as if you put a slower film in your camera for longer exposures. The object of the corrections is first to preserve the shadow detail. Call it Zone I if you will. That is a matter of adjusting exposure time to make up for the loss of film speed. Once that is done, normal development may or may not preserve the desired contrast index. Ilford does not mention any change of development in their recommendations for reciprocity correction, but the change of exposure time they recommend for all their films is almost exactly what my table calculates for a film factor of 0.51 . It is fairly certain that by increasing the exposure time by the amount calculated from my table for those films Howard tested you will obtain a printable negative without change in development.
    Gadget Gainer

  2. #72
    cao
    cao is offline
    cao's Avatar
    Join Date
    Oct 2004
    Shooter
    35mm
    Posts
    188
    I am aware of the meaning of RF; I just hoped there might be a good general theoretic model for how film deviates from a simple integrator of light energy. While I have a math background, I have none in physical chemistry, so I can't do anything but ask questions.

  3. #73
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    Quote Originally Posted by cao
    I am aware of the meaning of RF; I just hoped there might be a good general theoretic model for how film deviates from a simple integrator of light energy. While I have a math background, I have none in physical chemistry, so I can't do anything but ask questions.
    Me too. I thought the standard meaning of RF was "radio frequency" and was wondering how that came into play here.

    I am an engineer by education and nature. Our traditional job is to put theory into practice. Sometimes we don't even have a theory to work on, but still have to find a way to practice something. Other times, theory does not predict nature very accurately and we use empirical equations to fit data. With some degree of experience, we learn to recognize certain general mathematical forms that seem to fit the available data. Every human being does the same thing without knowing it, as when a baseball player learns to chase and catch flyballs. I cannot claim to have or even to know a theory of why my empirical equation fits data, although it has enough arbitrary coefficients to fit many situations.
    The most remarkable thing to me about what I have learned is that the basic RF (have it your way) curve fits all films I have data for with only 1 arbitrary constant for each film. It appears that the only things you need to know are the basic curve or equation which depends only on the indicated exposure but is independent of the film and a film factor which is independent of the indicated exposure time.
    Gadget Gainer

  4. #74
    Bruce Osgood's Avatar
    Join Date
    Sep 2002
    Location
    Brooklyn, N.Y. USA
    Shooter
    Multi Format
    Posts
    2,418
    Images
    44
    Oh, oh....... You mean it's not Range Finder?

  5. #75
    cao
    cao is offline
    cao's Avatar
    Join Date
    Oct 2004
    Shooter
    35mm
    Posts
    188
    Quote Originally Posted by gainer
    Me too. I thought the standard meaning of RF was "radio frequency" and was wondering how that came into play here.
    I've seen reciprocity failure written as RF and RLF. I meant to save typing rather than mislead. I'll be sure to define stuff more carefully now.

  6. #76
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,239
    Quote Originally Posted by cao
    I've seen reciprocity failure written as RF and RLF. I meant to save typing rather than mislead. I'll be sure to define stuff more carefully now.
    Caught me off guard too. ;-)

    When I saw RF, my first thought was radio frequency, but in the context of photography, I thought rangefinder. I did eventually scratch my head long enough to get RF to fit the context. Sometimes I'm slow on the uptake.
    When talking reciprocity failure I've seen reference to HIRF, for high intensity reciprocity failure (when using that megawatt flash with 1/100,000 second duration) and LIRF, for low intensity reciprocity failure, when you have to go to long exposure times because of low light intensity. I've just not seen RF alone in that context.
    I'm trying to come to terms (mathematically) with calculating the compounding of reciprocity failure when one Zone is adjusted with the Gainer formula and the others are allowed to fall accordingly. Just how much "expansion" (in Zone System terms) does reciprocity provide at given exposure times with a given Bond-Gainer film factor? I believe this is what "cao" is after. I'm not that great at math, but I'll post if I come up with anything useful.

    Lee

  7. #77
    cao
    cao is offline
    cao's Avatar
    Join Date
    Oct 2004
    Shooter
    35mm
    Posts
    188
    Quote Originally Posted by Lee L
    Just how much "expansion" (in Zone System terms) does reciprocity provide at given exposure times with a given Bond-Gainer film factor? I believe this is what "cao" is after.
    Lee
    Yes indeed I am. I also think the expansion might not be uniform across the zones, so you might get different densities from a normal exposure from one corrected out a long time. I see this as a potential creative choice. In my case, I'm shooting some macros of highly polished aluminum objects, and I see a potential for bending the film curve as a way to give different looks to the highlights. That is, I want to use LIRF as a tool rather than something to curse.

  8. #78
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    Quote Originally Posted by cao
    Yes indeed I am. I also think the expansion might not be uniform across the zones, so you might get different densities from a normal exposure from one corrected out a long time. I see this as a potential creative choice. In my case, I'm shooting some macros of highly polished aluminum objects, and I see a potential for bending the film curve as a way to give different looks to the highlights. That is, I want to use LIRF as a tool rather than something to curse.
    I don't recall Howard Bond saying anything that would imply Zone expansion. Certainly Ilford did not over the range of 0 to 35 seconds indicated time which by their adjustment resulted in 200 second exposure. Zone expansion would appear as a reduction of contrast index, which Ilford would surely have pointed out. Perhaps we should think of the zones as influenced only by relative light intensity once the exposure to record Zone I is applied.

    From what I have read, Ansel Adams compared visual zones to audible tones. Both are logarithmic functions, as are many things we can sense. We have seen the term Zones used as if it were a characteristic of film first and then of vision. His object was to get the Zones that he saw to appear on paper, which is manifestly impossible, but has been approximated by artists for centuries.

    I digress, as usual. In the long run, I do not think RF will do this fooling of the eye for us. There will still be dodging and burning of wide range scenes that can when done well make one want to squint at specular reflections reproduced on paper while still being able to see into deep shadows that we could not see in real life.
    Gadget Gainer

  9. #79
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    In case anyone is interested, I have a graph that shows how the equation I found fits the Ilford data as found in www.ilford.com. I'm going to try to attach it. If it works, you will see the curve with numbers on both sides every 5 second of measured time. On the left are the values I measured from an enlarged copy of the graph. On the right are the numbers I calculated using a film factor of 0.51.

    Here goes nothing!
    Attached Thumbnails Attached Thumbnails ILFORD_RF.gif  
    Gadget Gainer

  10. #80
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,239

    Gainer factor for Kodak "standard" film corrections

    And here's a conversion of the ancient Kodak chart for "standard" films to an equivalent Gainer factor, which is about 0.80. See the attached chart for the correspondence. For corrections up through 100 seconds of metered exposure, the Gainer method is within +/- 16% of the corrected Kodak times, about 1/6th stop. If you'd prefer to use the old Kodak standard:

    adjusted time = 2.0124*(metered time^1.3894)

    I got that from doing a curve fit to a set of old data I got in the 1970s. It's essentially a perfect match to the "standard" film reciprocity curve that Kodak still has in all the E-31 Technical data sheets, and the equation fits with an R^2 of 1.0 to the computer printout I have with 1 second increments from 1 to 100.

    Lee
    Attached Thumbnails Attached Thumbnails Gainer+KodakStd.png  



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin