Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,285   Posts: 1,535,072   Online: 1095
      
Page 10 of 12 FirstFirst ... 456789101112 LastLast
Results 91 to 100 of 120
  1. #91
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    Quote Originally Posted by gainer
    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!
    I got that film factor right in the text, 0.51, but spelled it 0.051 on the figure. The Ilford film factor is about 5 times what Howard Bond found in his experiments, but the shape of the curve is dead on.
    Gadget Gainer

  2. #92

    Join Date
    Jan 2005
    Location
    Boston, MA
    Shooter
    Multi Format
    Posts
    1,416
    Quote Originally Posted by gainer
    The true beauty of this serendipitous discovery is that all B&W films seem to share the same basic variation with indicated time, differing only in one constant for each different film.
    Reciprocity failure occurs because of inefficiencies in producing latent image centers from photoelectrons, and this inefficiency changes depending on the intensity of light irradiation. This phenomenon can be modified by different halide profiles of core-shell structures as well as different doping profiles at different depth of such crystals. Then there are different ways to chemically sensitize the emulsion. Reciprocity failure also varies depending on the crystal size, habit, etc. For example, cubic (100) AgCl tends to have more pronounced high intensity reciprocity failure if not combined with these methods to modify the behavior. It is typically seen as a long shoulder with the same toe. In case of (100) AgCl, a very well known emulsion stabilizing agent can improve the efficiency of latent image formation. After all, even a simple sulfur or gold sensitization can change the reciprocity failure. There are zillions of factors influencing this phenomenon.

    Just because some manufacturer publishes one correction chart for many of their products, it is pretty inappropriate to assume the underlying mechanism is the same.

  3. #93
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    .

    Just because some manufacturer publishes one correction chart for many of their products, it is pretty inappropriate to assume the underlying mechanism is the same.[/QUOTE]

    Ryuji, you could at least be gracious enough to read the article in Photo Techniques, Sept/Nov 2003 called "Reciprocal Trade Disagreement." You will see that I did NOT rely on manufacturer's so-called data, but on experimental determinations of reciprocity correction done by Howard Bond and published the previous issue. Theories are for the purpose of reducing observed behavior to first principles, as Aristotle said. I made no claim to have done that. I found an order in the data that someone might find a theory to explain, but in the meantime, I claimed it to be nothing more than an empirical relationship that fit the available data to within 1/3 f-stop over the range. I used the least-square criterion for the fit.
    Gadget Gainer

  4. #94
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    Quote Originally Posted by Kirk Keyes
    Lee, please do check your Acros - I've also seen mention of it's excellent long exposure properites. I was using an enlarger and step wedge, and I wasn't able to do any longer tests since I didn't have time to enclose the enlarger head to cut down more on the stray light... but I would like to see results from someone that obviously understands the subject.

    Kirk
    Here's a suggestion for anyone using an enlarger for tests where stray light can be a problem. Instead of enclosing the head, build a sort of tent out of matte board from the lens to the baseboard, with a flap so you can change stuff. If you need to change magnification, make the tent flexible. This works pretty well for a lot of cases, and has the advantage that the head will not overheat.
    Gadget Gainer

  5. #95

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Quote Originally Posted by gainer
    build a sort of tent out of matte board from the lens to the baseboard, with a flap so you can change stuff.
    Patrick - I thought of this as well. There are two options, seal up the head to eliminate tray light from the head, or seal up the film to minimize stray light from hitting the film.

    I figured that sealing the head would be better as I didn't want any potential stray light from the lens (i.e. any flare) bouncing back onto the film as it relected off the lens tent. I actually figured I would enclose the head, which really only need to be turned on for a few seconds before and after the exposure, so no need to worry about it overheating, and then a partial "tent" extending from the easal up several inches above the film. More like a fence, than a tent.

    Anyway, that's what I was thinking of.

  6. #96
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    This is a general comment on this and other threads as the occasion might arise. Beware of theories. It was said of sigmund Freud that he could explain everything, but could predict nothing. Kurt Godel (There should be an umlaut over the "o") proved that any set of axioms at least as rich as arithmeticis either incomplete or inconsistent. There are limits to our theories. Art is real. Science is imaginary. It is an invention of the human mind which is an invention of nature. The results of experiments are real, always erroneous to some extent, but they are the way we control our environment. We try to find order in them so that we can predict changes in the environment, whether it is the weather or the exposure to give our next photograph. The models we use are usually empirical. When we have a successful empirical model, some among us will try to find a more fundamental basis for it. We eventually arrive at the consequences of Godel's theorem and sit around arguing about which incomplete and/or inconsistent set of axioms is THE one. We are all wrong. Report the observations and the empirical curve fit. Theories are alright, but don't hold them to be infallible. Thanks for having me.
    Gadget Gainer

  7. #97
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    Quote Originally Posted by Kirk Keyes
    Patrick - I thought of this as well. There are two options, seal up the head to eliminate tray light from the head, or seal up the film to minimize stray light from hitting the film.

    I figured that sealing the head would be better as I didn't want any potential stray light from the lens (i.e. any flare) bouncing back onto the film as it relected off the lens tent. I actually figured I would enclose the head, which really only need to be turned on for a few seconds before and after the exposure, so no need to worry about it overheating, and then a partial "tent" extending from the easal up several inches above the film. More like a fence, than a tent.

    Anyway, that's what I was thinking of.
    I was thinking of the long exposures sometimes required for reciprocity tests. Things get pretty hot after 5 minutes or so with the vents blocked. Of course, a little more elaborate head cover could allow ventilation as well as adequate light sealing. My problem was light leaking around the negative carrier where it was difficult to cover.

    I used black matte board with the black side inside to cut down those reflections you are concerned about, but I am pretty well stuck with one head position.
    Gadget Gainer

  8. #98

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    yes - just a box with a baffle for air flow for the head is really all that's needed. I have a Saunders 4500 with a good fan. But, yeah, I forgot about the several minutes thing there!

  9. #99
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    Quote Originally Posted by Ryuji
    Reciprocity failure occurs because of inefficiencies in producing latent image centers from photoelectrons, and this inefficiency changes depending on the intensity of light irradiation. This phenomenon can be modified by different halide profiles of core-shell structures as well as different doping profiles at different depth of such crystals. Then there are different ways to chemically sensitize the emulsion. Reciprocity failure also varies depending on the crystal size, habit, etc. For example, cubic (100) AgCl tends to have more pronounced high intensity reciprocity failure if not combined with these methods to modify the behavior. It is typically seen as a long shoulder with the same toe. In case of (100) AgCl, a very well known emulsion stabilizing agent can improve the efficiency of latent image formation. After all, even a simple sulfur or gold sensitization can change the reciprocity failure. There are zillions of factors influencing this phenomenon.

    Just because some manufacturer publishes one correction chart for many of their products, it is pretty inappropriate to assume the underlying mechanism is the same.
    Ryuji, let me ask an earnest, honest question. I look at the equation that describes the current through a junction diode as a function of the voltage across it. I have used this in analog computing, and it is quite accurate for making a logarithmic amplifier over a considerable range of 3 to 4 decades when I use the collector-base junction of a silicon transistor. The model equation does not fit reciprocity, as it is the kind of eponential equation that plots as a line on log paper, but the fact that Boltzmann's constant and absolute temperature are the factors that shape the response and it is pretty well constant for high and low current diodes. I think the voltage drop across the diode is dependent on the area of the junction (at least). When I read about reciprocity, I see many things that remind me of that diode equation. Why should there not be a similar type of thing here? One part of the equation with its characteristic response and another which describes the magnitude of the response?
    Gadget Gainer

  10. #100

    Join Date
    Jan 2005
    Location
    Boston, MA
    Shooter
    Multi Format
    Posts
    1,416
    Gainer, you are bringing up irrelevant issue here. What you are talking about is forward voltage drop at the pn junction. Reciprocity law failure is mostly due to the loss of the carrier or unstable latent subimage. All these are described on my webpage and references therein in greater details. The former is negligible in the exponential region of the pn junction, and the latter concept does not exist in pn junction.

Page 10 of 12 FirstFirst ... 456789101112 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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