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  1. #61
    Bill Burk's Avatar
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    Quote Originally Posted by markbarendt View Post
    Why would we (or a meter or film manufacturer) want to find our exposure settings based on points that should be trusted less?

    It seems to me that the old adage "shoot to the shadows and develop for the highlights" like most simplifications, can lead us a bit astray here.
    I would say underexposing shadows can quickly ruin a negative - so it is often the most important exposure to determine. This applies mostly to scenic/landscape photography.

    Other kinds of photography where a tripod is not used, will be more quickly ruined by slow shutter speeds - so for majority of purposes it is more important to emphasize speed.

  2. #62
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    This model is wrong, because it shows what arrives at the film plane, including the one stop of flare in the shadow.

    So for example a Scene Zone 0 came up to Film Plane Zone I.

    But did a Scene Zone 0 come up to a Meter Zone I? The meter readings are not without flare. Whenever I aim a spotmeter at the darkness under a car for example, a lot of flare influences the meter reading.
    Bill, I'm really curious as to what you see being wrong. We have to be getting our lines crossed somewhere. I'm interested to learn if there is any miscommunication with the way I'm explaining this. I've added Zone markings to the standard exposure model with one stop of flare so you can compare it with your version.

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    Flare does have an effect with the optics of spot meters, but just like with the camera, it's larger in the shadow areas than around the mid-tones. The exposure constant of 8 has already factored flare in. You're answered Mark's question about metering the shadows. Flare is too variable, hard to measure, and impossible to predict for the shadows to be a viable option. The next set of examples are three different flare models: no flare, one stop of flare, and two stops of flare. The exposure around the metered exposure point changes little while the shadow placement varies considerably.

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  3. #63
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Bill, I'm really curious as to what you see being wrong.
    I only mean the diagram I drew was wrong, I didn't want it to be taken as a solution.

    My diagram is too ideal. Zone 0 at the 0.3G, Zone I at speed point and Zone V at the meter point is too perfect to be right - so it's wrong.

    That's all. The rest of this is good.

    ---
    Since spotmeters are subject to flare, could it be (since the sensor of a spotmeter got similar flare to film), you really do get a reasonable prediction of shadow exposure?

  4. #64
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    Quote Originally Posted by Bill Burk View Post
    I would say underexposing shadows can quickly ruin a negative - so it is often the most important exposure to determine. This applies mostly to scenic/landscape photography.

    Other kinds of photography where a tripod is not used, will be more quickly ruined by slow shutter speeds - so for majority of purposes it is more important to emphasize speed.
    I'm not suggesting that anyone changes the exposure point they want to peg. What I'm suggesting is that it could be more reliable finding it indirectly.

    As Stephen suggests the offset to the speed point is a known and any personal preference we may have for exposure offset can be applied to that offset.

    Quote Originally Posted by Stephen Benskin View Post
    So, how do we know the speed point – metered exposure ratio is 1.20 log-H or 16x (15.8) for Zone System testing? It’s right there in the Zone System testing instructions. Meter a card and stop down four stops. Zone I is the speed point and it is at 0.10 over Fb+f. Four stops of exposure is 1.20 log-H.
    This is a relationship, the offset or constant, between meter reading and film speed point is fixed.

    A given reading to a known mid-tone point gives us our shadow.

    I am also not suggesting that measuring the shadow point is without value just that it may be better used as a check and in the SBR determination rather than as the primary reference.

    Because

    Quote Originally Posted by Stephen Benskin View Post
    Flare makes determining where the exposure would actually fall a nightmare. There's very little flare at the metered exposure point.
    Human vision compresses tones in the lower range. We are a lot more sensitive to tonal differences in the middle range.
    Many scenes don't have shadows deep enough to even reach the speed point exposure. You'd be metering at a point where there's no subject luminance.
    And flare again, because it is just that important.
    Our meters and our tone perception work better in the mid-tone range, we can differentiate better and flare doesn't affect mid-tone readings like it does for zone 1 readings.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  5. #65
    Bill Burk's Avatar
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    Quote Originally Posted by markbarendt View Post
    I'm not suggesting that anyone changes the exposure point they want to peg. What I'm suggesting is that it could be more reliable finding it indirectly.
    I'm not going to discourage you from exploring your idea.

    But I have trouble gauging gray. When I meter off what I think should be the gray of my scene, say the middle of an old paved street, I am surprised to find it is my highlight!

    BTZS uses the incident meter to indirectly determine shadow exposure. You are right that there are benefits to using indirect metering.

    But I still think the spotmeter, from camera position, will give a good indication of what will reach the film plane thanks to flare. I just did a check and saw the needle move at least a stop or two between spotmeter from camera position and walking right up to what I was metering. When I was close, the reading was less influenced by flare - so it may have been a more accurate reading of the subject luminance. But at camera position, the spotmeter could have been giving me a good shadow reading.

  6. #66
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    Quote Originally Posted by Bill Burk View Post
    But at camera position, the spotmeter could have been giving me a good shadow reading.
    I agree with you 100%.

    I do my ZS testing with a 4x5 step tablet contacted to the film targeting a white matboard with lens at infinity in uniform shade (I use a Pentax V spot meter), I have yet to be disappointed with my resulting EIs and subsequent shadow placements. I barely give flare a moments worth of thought, except just prior to releasing the shutter, when I try to shield the lens the best that I can. But I still find this thread interesting enough.

  7. #67
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    As Stephen suggests the offset to the speed point is a known and any personal preference we may have for exposure offset can be applied to that offset.

    This is a relationship, the offset or constant, between meter reading and film speed point is fixed.

    A given reading to a known mid-tone point gives us our shadow.
    Mark,

    That's exactly right. I was worried that nobody was going to appreciate the significance of the speed point-metered exposure ratio.

    I also hope the idea that the speed point isn't an arbitrary target density didn't go unnoticed. That the process of determining the speed point also defines important aspects of the film curve. With b&w film it's the relationship with the minimum useful gradient point or 0.3G. Keeping that in mind, the 0.3G point tends to change in relation to the 0.10 speed point with changes in development. It's only has a exposure difference of around one stop when the ISO contrast parameters are followed. With increased or decreased development, the one stop relationship on longer exists which means the important connection between the 0.10 speed point and the lower useful end of the film curve is lost as well as the direct correlation connecting the exposure to the quality of the practical picture results of the first excellent print tests.

    There is a fix which still enables the continued use of the 0.10 speed point. It just requires using an equation that is in the ISO standard but is built into the ISO contrast parameters. Because the 0.3G point has an inverse relation with the film gradient, it tends to shift to the right with extended development and to the left with decreased development.

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    This tends to mute the degree of speed change in regard to development comparied to just using the 0.10 speed point without the “fix.” This fix is known as the Delta-X Criterion.

    Another concept that I hope came across was that if the photographer is doing sensitometric film testing, it’s better to test using well determined speed methods such as the ISO standard, fractional gradient, or Delta-X and to either adjust the meter’s EI or the speed constant, to change the speed point-metered exposure ratio, if more or less exposure is desired.

  8. #68
    markbarendt's Avatar
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    Quote Originally Posted by Bill Burk View Post
    But I have trouble gauging gray. When I meter off what I think should be the gray of my scene, say the middle of an old paved street, I am surprised to find it is my highlight!
    Bill you make "my" point perfectly.

    I use a Beseler PM2L to set enlarger exposure and when measuring negatives I constantly get surprised on where I find the darkest and lightest points.

    But alas it's not really "my" point. It's a point that I finally "got" when reading Dunn and Wakefield's, Exposure Manual, and that point has been reinforced by Stephen and others and in practice.

    Finding or putting a "known" of some type into the scene is key to finding camera settings in a quick, reliable, and repeatable manner.

    And it's not an incident vs spot meter thing. Dunn and Wakefield teach that they are fully interchangeable.

    An incident meter brings along it's own "known" target but we still need to know what we are reading. The first question with an incident meter should be, is the reading being taken in the same light as the scene/subject? If not, an adjustment needs to be applied, the same exact adjustment as a spot meter would need for a known target in that same light.

    Knowing "What point/zone are we reading" is always key.

    Cute story. Time has passed so the details may be remembered differently by others but I attended a workshop with Jim Galli and Per Volquartz and a bunch of great guys a few years back and one of the things we did was a portrait of Per in the Goldfield NV court room.

    During the initial set up there was a scramble by everyone around to grab their meters and most were spot meters. This was followed by lots of readings and fun discussion of the minutia and Maths.

    Yes my incident meter was among the fray.

    In the end, even though there was a bit of variation individually the consensus of the spot meter reading group matched my incident meter reading exactly.

    Jim Galli was one of the guys stepping up to the plate to take a shot after all the fuss over metering.

    He used an old barrel lens with two dark slides as his shutter. http://www.apug.org/forums/forum44/2...ll-please.html

    Truly a case of measure with a micrometer, mark it with a crayon, and cut it with an axe.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  9. #69
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    It's a point that I finally "got" when reading Dunn and Wakefield's, Exposure Manual, and that point has been reinforced by Stephen and others and in practice.

    Finding or putting a "known" of some type into the scene is key to finding camera settings in a quick, reliable, and repeatable manner.

    And it's not an incident vs spot meter thing. Dunn and Wakefield teach that they are fully interchangeable.
    I suggest anyone who owns Exposure Manual to take another look at Appendix B. Much of it is exactly what has been discussed on this thread. Figure 8.1 shows the relationships between the fractional gradient speed point, the 0.10 density speed point, and the metered exposure among others.

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    Under the heading (i) Scene Luminance, Film Speed, and Camera Exposure Relationships, Dunn writes:

    "Thus when an exposure meter which meets the quoted standard specifications is used to measure the reflected light from the simulated "average scene" gray test-surface in daylight, and the computer dial of the meter is used in conjunction with the rated speed of the film to determine the camera settings, the resulting exposure Hg, on the film for that scene element is expected to be 10 times greater than the exposure Hm involved in the sensitometric derivation of the film speed.

    The ratio Hg/Hm is important because it indicates the level of exposure which will be obtained by the use of the rated speed with a calibrated exposure meter in normal daylight photography...This is the situation at the time of writing, and it may be regarded as wholely satisfactory as after the removal of the larger safety factor included in earlier days it is now left to the photographer himself to apply any safety factor he may consider desirable for the work he is doing. Using a large format camera he can, if he wishes, play safe and revert to a safety factor of 2 or even 4 without endangering print quality. If on the other hand he is working with a 35mm camera and is seeking negatives capable of big enlargement he can follow his exposure meter intelligently with only such modifications as may be suggested by unusual scene contrast or unbalanced luminance distribution."
    Last edited by Stephen Benskin; 01-15-2012 at 12:58 PM. Click to view previous post history.

  10. #70
    markbarendt's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    I suggest anyone who owns Exposure Manual to take another look at Appendix B.
    I'd suggest that anyone who is really interested in understanding the how's and why's of exposure and metering should get and read as late an edition as they can find, if they don't already have it.

    It is not just another "Zone System" knock off.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

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