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Thread: Question On Subject Brightness Range

  1. #41

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Stephen Benskin View Post
    Sorry, I spent around two hour writing a post and when I went to upload it, the site had logged me off and I lost 95% of it. All that survives is the bit of intro below. Not really in the mood to redo tonight.

    For any speed or contrast methodology to be relevant, the psychophysical nature of the photography must be considered. This is what Jones did in with The First Excellent Print test. He established a criterion of excellence for the photographic image, and established the definition of exposure.

    Jones concluded negative density is not a practical criteria for determining quality. Contrast is, or more accurately, film gradient. More specifically quality is determinant by the gradient of the toe in relation to the overall gradient of the film. This conclusion came after comparing various speeds methods with the test print judgement speeds under the greatest number of conditions with the greatest number of emulsions and degree of processing to determine the method that most accurately corresponded to the results from the prints judged to be excellent.
    Thanks Stephen, I know how you felt... condensing all that knowledge is a great effort.

    I agree... paper can show 1:100 contray. st, but scenes can have have much more, so the way those gradients are used to take the paper (or monitor) range is critical to get a natural image and depth...


    Perhaps one key issue about shadow detail quality may be flare, I'm thinking that a 3 stops underexposed area may receive flare enough to decrease microcontrast. Perhaps film can record it, but the scene nature and lens flare can damage that shadow gradient quality.

    I'll read about Jones, thanks !

  2. #42

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Bill Burk View Post
    I found a spot meter that has 0.4 flare similar to the camera image, so I agree your meter might already help you integrate flare into your readings. In practice, you might compensate for "already-included" flare by simply placing the shadow reading a stop higher than you otherwise thought, for instance on Zone IV instead of Zone III*. I wouldn't bother over that last third-stop at this point.

    The 3 1/3 stops down to the speed point is sensitometric exposure as opposed to what you get in the camera-image.

    *Maybe the switch in practice from close-up reading with Weston Master meters to camera-position spotmeter readings had something to do with the change from Zone II shadows to Zone III that I noticed between older references and more up-to-date ones. (So if you use a Weston, place in Zone II or III... if you use a spotmeter place shadows in Zone III or IV).
    Now I understand the importance it could had using a probe for metering in the GG, as this metering is TTL and includes flare.

    IMHO placing the SLR in the back of the view camera it will be near the same, this is not perhaps necessary for all shots, but IMHO it is a good way to understand the importance of flare, and learning when it is going to have an impact.

    Perhaps the change from Z-II to Z-III is due to the 1961 ASA speed change, box speed where changed to the double without any change in the product... this would be a factor if comparing pre to post 1961 literature...

    I've a Weston that not works well, but I'll get another one. My plan is uisng the Nikon F5 in the back to make accurate readings and understanding the weston readings, but I feel very pleasing using a weston...

  3. #43

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Pere Casals View Post
    Now I understand the importance it could had using a probe for metering in the GG, as this metering is TTL and includes flare.

    IMHO placing the SLR in the back of the view camera it will be near the same, this is not perhaps necessary for all shots, but IMHO it is a good way to understand the importance of flare, and learning when it is going to have an impact.

    Perhaps the change from Z-II to Z-III is due to the 1961 ASA speed change, box speed where changed to the double without any change in the product... this would be a factor if comparing pre to post 1961 literature...

    I've a Weston that not works well, but I'll get another one. My plan is uisng the Nikon F5 in the back to make accurate readings and understanding the weston readings, but I feel very pleasing using a weston...
    I would like to emphasize Bill's spot meter flare came from a scene with a full luminance range and not from a test target.

    The Zone System didn't change with the change in the speed standard. Even though the older ASA method that used the fractional gradient method and the new ASA method were different, they produced similar speed results. When the standard changed, the results no longer correlated. The change in results naturally lead to conspiracy theories. Many that persist to this very day. When was the last time you read ISO speeds are different than in practice because they are laboratory tested and not testing in a real world situation?
    Last edited by Stephen Benskin; 14-Jun-2017 at 11:49.

  4. #44

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    Re: Question On Subject Brightness Range

    Yes my example scenario was a full range scene. Really, any meter is useful when you adapt to using it. I get a little tripped up when my Zone sticker falls off though.

    A Weston meter is calibrated to a different color temperature than modern meters so that can complicate comparisons a little. Your SLR is probably fine.

    The flare I see in the meter... I also see by eye. It's really obvious.

  5. #45

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Bill Burk View Post
    Yes my example scenario was a full range scene. Really, any meter is useful when you adapt to using it. I get a little tripped up when my Zone sticker falls off though.

    A Weston meter is calibrated to a different color temperature than modern meters so that can complicate comparisons a little. Your SLR is probably fine.

    The flare I see in the meter... I also see by eye. It's really obvious.
    Something else to keep in mind, the full range needs to be within the meter's field of view (spot meter because it has an optical system to create flare). If you are measuring a small dark area and the highlight is outside the optics of the spot meter, then there's no highlight to flare into the shadows. Also keep in mind, the optics of a spot meter aren't the same as the camera lens, so whatever flare is produced in the meter's optics, isn't representative.
    Last edited by Stephen Benskin; 15-Jun-2017 at 12:57.

  6. #46

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Stephen Benskin View Post
    Something else to keep in mind, the full range needs to be within the meter's field of view (spot meter because it has an optical system to create flare). If you are measuring a small dark area and the highlight is outside the optics of the spot meter, then there's no highlight to flare into the shadows. Also keep in mind, the optics of a spot meter aren't the same as the camera lens, so whatever flare is produced in the meter's optics, isn't representative.

    Haa all these representatives... True the flare I see in my spotmeter is a good "representative" of flare only when my highlights shadows and other tones that I can see in the viewfinder of the spotmeter are distributed in about the same proportions as you might find in the entire camera scene. I thought I had a pretty good test where the result would have been about the same even if I had taken in a wider view. I think the distribution of luminances changed from being isolated to a single dark tone when I was close-up to about average when I stepped back.

    If you fill your spotmeter viewfinder with a single tone, easiest way is to move in close, then you remove the flare from the measurement.

    Likewise, although the spotmeter optics are not the same as the camera, I think the "calibration" of the meter included assumptions about what the camera optics would be (so it was likely designed to be reasonably representative even though not literally a true representative).

  7. #47

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    Re: Question On Subject Brightness Range

    Jones was the first to approach the determination of film speed using psychophysics. Previous film speed methods were generally based on an assumption of a characteristic of the film curve. As photography is about the image, the best way is to work backward starting with images considered to be of high quality. The first excellent print test was an exhaustive test where multiple film stocks were exposed differently and processed in different developers to a range of gradients. Then they were printed with a range of print exposure and grades. The prints were then judged for the best quality. Jones found shadow detail was the most critical component in quality determination.

    The first excellent print was at a point where print quality drops off quickly as shadow exposure moves to the left of that point. On the other hand, quality increases slightly as the shadow exposure moves to the right and then levels off. The limiting factor with increased exposure is mostly dependent on film size and degree of enlargement. As exposure increases, grain tends to increase and sharpness tend to decrease. The smaller the format, the more pronounced the effect.

    Click image for larger version. 

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    The first excellent print represents the extent of the lower limits of exposure that will still produce a quality print. The next step is to find a way to obtain the same results through sensitometrical means. After comparing the predicted results from various speed methods with the print judgement speeds, Jones found the method that came closest to the print judgement speeds under the greatest range of condition is where the shadow gradient is 0.3x the film's average gradient. To be clear, this is not a point of density as the shadow gradient increases and decreases with changes in the degree of development. In fact, Jones states that density is not a measurement of quality.

    The determination of exposure and film speed is accomplished using this point as a base, not the aim. Any shadow exposure that falls within reason above 0.3x average gradient will produce a quality image. By using the fractional gradient point as the speed point, it's easy to include a constant into the speed equation to have the exposure fall further up the curve.

    The ISO speed fixed density point falls 0.10 above fb+f. The fractional gradient speed point falls approximately one stop to the left, so why wasn't the pre 1960 speed about twice as fast as the post 1960 speed? The ISO speed equation is 0.8/Hm. For a 125 speed film, Hm would equal 0.0064 lxs. The exposure at the fractional gradient speed point would be 0.0032 lxs. Film speed at this point would be 1/0.0032 = 312. Fractional gradient speed is not the pre 1960 ASA speed. Technically speaking, the fractional gradient speed point is the only true speed point. Everything else is an EI. The pre 1960 ASA speed and today's ISO speed is an EI based on the fractional speed point. With the pre 1960 ASA speed, a constant is included in the equation: 1/ (4 * exposure at fractional gradient point). For our .0032 lxs exposure, the resulting speed is 78.

    Why did the speed method change in 1960 if the fractional gradient method is superior? Because of the complexity of determining 0.3X, experimental error was easily introduced into the process. The US and Britain wanted an international standard, but Germany didn't like the fractional gradient methodology. C.N. Nelson and J.L. Simonds found an equation that could identify where 0.3X would fall in relation to the easily us use 0.10 over fb+f. When the now ISO contrast parameters of Δ1.30 log-H and Δ0.80 density are maintained, the fractional gradient always falls Δ0.29 to the left of the fixed density point. Any processing above or below the ISO parameters needs to use the Delta-X equation. The ISO standard uses it too as it is part of the parameters. Without incorporating the fixed density method into the Delta-X equation, "the fixed density criterion tends to underrate films that are developed to a lower average gradient and to overrate films that are developed to a higher average gradient," according to Nelson. The safety factor was reduced because accurate exposure meters were more available and small formats were more prevalent. If the fractional gradient criterion was kept, the reduction of the safety factor could have been done by simply changing the constant in the speed equation to 0.4/fractional gradient exposure: .4/0.0032 = 125.

    So how does the exposure meter work with the film speed to determine exposure placement on the film, especially when the meter needs to work with b&w negative, color negative, and color reversal films?

  8. #48

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Stephen Benskin View Post
    Jones was the first to approach the determination of film speed using psychophysics...
    Very interesting reading... I've been reading it with a lot of interest.

    I found that now we have a new tool in darkrooms: variable contrast paper !

    The great thing about variable contrast paper is split grade printing, so we can burn/dodge when the low or high contrast share is exposed. Also SCIM...

    IMHO the classic technique you describe it's very interesting... because I guess it is linked with the way Karsh used toe...

    Today I see a trend, taking all linearly and then cooking the image in the postprocess, but the way you tell it's very interesting, I'll investigate more about that, thanks for making the effort to write (twice) all that, it has been very interesting to me !

  9. #49

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Stephen Benskin View Post

    So how does the exposure meter work with the film speed to determine exposure placement on the film, especially when the meter needs to work with b&w negative, color negative, and color reversal films?

    Color negative film ISO 5800:2001

    Black-and-white negative film ISO 6:1993

    Color reversal film ISO 2240:2003

  10. #50

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    Re: Question On Subject Brightness Range

    Quote Originally Posted by Pere Casals View Post
    Very interesting reading... I've been reading it with a lot of interest.

    I found that now we have a new tool in darkrooms: variable contrast paper !

    The great thing about variable contrast paper is split grade printing, so we can burn/dodge when the low or high contrast share is exposed. Also SCIM...

    IMHO the classic technique you describe it's very interesting... because I guess it is linked with the way Karsh used toe...

    Today I see a trend, taking all linearly and then cooking the image in the postprocess, but the way you tell it's very interesting, I'll investigate more about that, thanks for making the effort to write (twice) all that, it has been very interesting to me !
    How did Karsh use the toe?
    Bill
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

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