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  1. #61
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    Quote Originally Posted by Stephen Benskin View Post
    My favorite is the rumor that Alan Ross has discovered a negative density range of 1.45 for normal. That one always makes me laugh. If there's nothing else I've gotten out of studying theory it has to be a pretty good BS meter.
    "Discovered" a negative density range? Where did you determine that? That sounds good to say I guess, but is baseless, IMO.

    Criticism only has merrit if your facts are right, wouldn't you agree?

    It is, from what I can tell, simply an idea he has of considering calibrating a "normal" development time by targeting a Zone IX density of 1.45 rather than at a Zone VIII density of 1.3 for the reasons that you can laugh at here; but please, do tell where you can prove a discovery is being proclaimed. I've no idea if he ever followed through with it, but I would find it interesting to see his results.

  2. #62
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    The subject of the sentence was about how rumors and hearsay are sometimes presented as information. That is the funny part, not Ross. The use of the word "discovery" was used in a humorous way.

    To seriously address the substance of the rumor, see posts 1,7,9,10,11,13,16, and 18.

  3. #63
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    To be fair to Alan Ross, he's not claiming a density range of 1.45. He's claiming a target upper density of 1.45

    The lower end of his density appears undeclared but if I guess it is around Zone II, 0.3 - this would lead to a density range of 1.15 only .1 more than the normal 1.05 we've been talking about.

  4. #64
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    Quote Originally Posted by Bill Burk View Post
    but if I guess
    Is that anything like assume?

    I'd like to get back to why finding out the reason for the differences between the value of C in the older standards and the value in the current standards. I knew that the average illuminance couldn't have changed, so there had to be another reason for the lower value. But was it something having to do with the physical properties of the exposure meter or how the exposure meter is used? Finding out that the earlier testing was done with the flat disk (cosine) receptor means there is a consistency of agreement over time. That most of the real differences in the value of K and C can be attributed to the conditions under how the meters are tested.

    Another interesting tidbit of information from the paper is that the value of C can change with the thickness of the receptor. Here's a graph from the paper Comparing the photographic performance of various light receptors for incident light method of exposure determination. The bottom axis is the angle of the sun in relation to the direction of the camera. The exposure meter is placed in front of the subject pointed toward the camera.

    Click image for larger version. 

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    The findings:

    "From the curves shown, it would appear that the flat pick-up does demonstrate an error in exposure determination which increases progressively. For the pick-up with constant 35 the meter indication give reasonably near correct exposure for frontal lighting and become progressively more in error towards over-exposure as the angle of incidence increases, whilst the pick-up with constant 22 give under -exposure for frontal lighting progressively tending towards over-exposure for back lighting.

    For both receptors the error is appreciable at 180 degrees, that is, for back lighting.

    It will be observed that the pick-up with cardioid type characteristic gives approximately the same error in exposure at all angles of incident illumination and further that when the constant is about 35 to 38 reasonably nearly correct exposure is obtained."

    The conclusion:

    "...the results of the test as summarized in in the curves of Fig 1 demonstrate that the receptor with cardioid type pick-up characteristic can give satisfactory exposure determination by means of a single reading for any angle of incidence of the maximum illumination on the subject.

    For this condition to be met, the photographic constant C as defined and determined in standard ASA Specifications must be about 35 to 38, whilst a tolerance of +-5 is permissible on the figure adopted.

    The flat plate type of receptor an be seriously in error when the angle of receptor is over about 90 degrees but may give reasonable results for angles less than about 90 degrees."


    The ability for the cardioid receptor to produce acceptable results in in all conditions was probably why it was adopted as the primary value of C. The next question is why the difference between the recommended value of 35 and the adopted value, in the ANSI 1971 standard of 30. Interesting enough, that standard appears to switch from the cosine value of C to the cardioid value instead of keeping the value for the cosine receptor and creating a separate value for the cardioid receptor.
    Last edited by Stephen Benskin; 02-11-2012 at 01:54 AM. Click to view previous post history.

  5. #65
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    Quote Originally Posted by Bill Burk View Post
    To be fair to Alan Ross, he's not claiming a density range of 1.45. He's claiming a target upper density of 1.45

    The lower end of his density appears undeclared but if I guess it is around Zone II, 0.3 - this would lead to a density range of 1.15 only .1 more than the normal 1.05 we've been talking about.
    The print is very small, but on the graph it states that the Zone I density target is .09.

  6. #66
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    Alan Ross has talked of placing shadows on Zone III (or IV, I can't find the reference right now). But keying highlights at 1.45 is not a bad idea for 4x5 and larger negative film. It may be bad for 35mm (if minimizing grain and maximizing other attributes is critical for you). But landscape, pictorial, black and white on a tripod is not hurt at all by placing exposure higher than the minimum.

    I also think you are onto something thinking earlier meters had only a flat disk. Possibly the "engineering" developments and early meters were used for architectural lighting/illumination work where the meter is aimed to the light source.
    Last edited by Bill Burk; 02-11-2012 at 12:57 PM. Click to view previous post history.

  7. #67
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    Quote Originally Posted by Bill Burk View Post
    To be fair to Alan Ross, he's not claiming a density range of 1.45. He's claiming a target upper density of 1.45

    The lower end of his density appears undeclared but if I guess it is around Zone II, 0.3 - this would lead to a density range of 1.15 only .1 more than the normal 1.05 we've been talking about.
    I found it at http://www.alanrossphotography.com/c...emandmetering/

    You're right. It's hard to read. And it’s not about an idea for a new negative density range, but a different set of points to determine contrast. Ross was having problems with negatives from scenes with longer than normal luminance ranges. He found that by adjusting point where the contrast is determined, the resulting negative contrast produced tended not to block up.

    This is definitely an important issue. I attempted to create a discuss it in a recent thread, “Average Gradient Methods.” The goal of any method of contrast determination is for the area of the test to agree with the area of usage. As the area of usage changes the ideal method would change with it as well as take in various factors such as flare.

    The method that has good agreement between the testing results and the results from use in the greatest range of situations is considered the optimum approach. Almost any method will produce good results under more specific and limited conditions. Generally this tends to fall around the statistical average conditions. The further away from this situation, the greater the degree of error.

    A discussion on the strengths and weaknesses of the different methods of contrast determination could be a worthy one.

    There's something about Ross's examples that falls under hiding in plane sight, the Zone indicated steps along x-axis. They are all equally spaced? The two example don't incorporate flare into the testing.
    Last edited by Stephen Benskin; 02-13-2012 at 12:51 AM. Click to view previous post history.

  8. #68

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    I'm often working under extreme contrast conditions and agree the area of usage is a key concept, often missed by people when they talk about extreme contractions, targetting paper grades etc. It is why when I do my speed and development tests I plot out to around 10 stops over metered. I think we got into this discussion back in the CI thread, which was interesting.

  9. #69
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    I think we got into this discussion back in the CI thread, which was interesting.
    We did. It didn't go into as much detail about the strengths and weakness of the different methods as I would have originally hoped.

  10. #70
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    Quote Originally Posted by Bill Burk View Post
    Alan Ross has talked of placing shadows on Zone III (or IV, I can't find the reference right now).
    I can't find the reference because I don't think there is any. Alan Ross didn't talk of placing shadows high. I believe I confused him with John Sexton. Apologies. I can't say where Alan Ross places his shadows, and I didn't mean to put words in his mouth.



 

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