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  1. #151
    Bill Burk's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    The whole meter issue really bothers me. ... Just reading the list of meter modifications (various filters, baffling) was depressing enough.
    Trust one good meter and leave it at that.

    I could wish for a spectrophotometric meter that could be programmed for my favorite film and which also could interpret the effect of black and white contrast filters to predict the Zone System placement. Totally possible with current technology. But that would reduce metering to a "point and shoot" frame of mind, which takes some of the fun (and all the participation) out of it.

    Lately, as I experiment with my Weston Master II and Zone System sticker, I once again "walk in the footsteps" of Ansel Adams. I can walk up to a gray wall, set the meter to V. Point at sky and see needle go up to IX. Point at a green plant and stop to think... The Master II selenium cell is making the plant go to VI but I know it is really still V. Finally learning these tricks that used to drive him and Fred Picker to make these modified meters. But they always dealt with it until the Zone VI modified meter came out.

  2. #152

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    Ok, in the flare example the more I think about what Stephen said I think we can at least remove reflection off the emulsion. So we've removed that element, and removed the diaphragm as a variable by using and ND filter. So the possibility we're left with is simple camera flare. Here is where I'm still unsure - because assuming I don't mask the lens to an image rectangle with projection limited to the emulsion area, the image circle is larger than the film, so indeed additional extraneous light could bounce off surfaces in the mirror box, onto the film and cause increased exposure. Is this reasoning correct?

    If that is correct, the question again would be, given the equivalent image forming units of light in the two exposures (1/60 @ f/2, 1s @ f22), would there be a difference in film density for this relatively low density (actual density or "Zone" not really critical, as long as the net density above FB+f is quite low - say somewhere around 0.1-0.2 above FB+f).

  3. #153
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Ok, in the flare example the more I think about what Stephen said I think we can at least remove reflection off the emulsion. So we've removed that element, and removed the diaphragm as a variable by using and ND filter. So the possibility we're left with is simple camera flare. Here is where I'm still unsure - because assuming I don't mask the lens to an image rectangle with projection limited to the emulsion area, the image circle is larger than the film, so indeed additional extraneous light could bounce off surfaces in the mirror box, onto the film and cause increased exposure. Is this reasoning correct?
    I can't speak with any certainty to camera design and all the elements that contribute to flare, but generally what you are describing are things that could add to the level of flare.
    If that is correct, the question again would be, given the equivalent image forming units of light in the two exposures (1/60 @ f/2, 1s @ f22), would there be a difference in film density for this relatively low density (actual density or "Zone" not really critical, as long as the net density above FB+f is quite low - say somewhere around 0.1-0.2 above FB+f).
    The flare factor is calculated by how much the shadow exposure is affected. I believe the standard practice is to use the shadow exposure 4 1/3 stops down from the meter exposure point of a statistically average scene luminance range. A one stop filter factor means flare doubles the shadow exposure 4 1/3 stops below the metered exposure. If the luminance range is shorter than the statistically average and the shadow exposure doesn't reach down 4 1/3 stops, then there's nothing there to add exposure to. Where the shorter luminance range shadow falls in this example will not experience a doubling of exposure.

    Within the same optical system, the only way to change the flare factor is by a change in the luminance range or change in the portion of dark and light tones in the scene and how they are distributed. Adding or reducing the camera exposure should just move back and forth along the x-axis.

    Currently reading about K in Henry's book. If I didn't already understand what the K-factor is, I still wouldn't know after reading that section. Another example of how he just might not be into theory. Still have the testing for K to get through.

  4. #154

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    Quote Originally Posted by Stephen Benskin View Post
    A one stop filter factor means flare doubles the shadow exposure 4 1/3 stops below the metered exposure. If the luminance range is shorter than the statistically average and the shadow exposure doesn't reach down 4 1/3 stops, then there's nothing there to add exposure to. Where the shorter luminance range shadow falls in this example will not experience a doubling of exposure.
    I'm not following. Did you mean to say a one stop flare factor? Let's assume the two exposures I listed are both 4 1/3 stops below metered and that the film density under zero flare conditions would arbitrarily be 0.20 above FB+f in either case. In the first exposure, the intensity of light entering the camera is high, and so some of this light (from the portion of the image circle beyond the borders of the emulsion) might bounce around, eventually bouncing onto the film and adding some additional exposure. At least I think it might. Maybe the actual film density ends up being 0.23 above FB+f. In the second exposure, a much lower intensity of light enters the camera, but the shutter is open for longer. Would we still expect a density of 0.23? Or would we actually get the zero flare density of 0.20 because the light intensity is not high enough to cause significant reflections in the camera - even though the film is exposed for longer.

    Perhaps there is no definite answer. Here's another way to think about the same example. You take a picture of a bright, uniform, featureless mid day sky and expose it to produce an expected net film D of 0.20. In the evening you take a picture of a middle grey, uniform, featureless evening sky and expose it to produce a net film D of 0.20 (so obviously this would be a significantly longer exposure than the picture of the mid day sky). Assume some camera flare in the first exposure leads to an actual net film D of 0.23. Would that occur in the second example too, even though the intensity of light entering the camera is lower? I'm thinking there would be less, or zero flare in the second exposure. Not sure.

    Keep in mind this question concerns an in-camera film test with as little flare as possible (aside from some degree of lens flare which cannot be totally eliminated). The aim is to use a brightly lit white card for the entire series of exposures. In actuality, the lens is masked to restrict the projected image to within the borders of the emulsion. In other words, there should be no camera flare. But even though I would be using this mask anyway as an extra precaution, I'm wondering if it is necessary. So my example above would be the equivalent of not masking the lens.

    Sorry again for repeating myself. I just want to make sure I really understand this.

    Regarding the K-Factor discussion in Henry's book, as it happens I re-read that very section today, and I came away just as little understanding as when I first read the book. I wish he had started by explaining what the K-Factor actually is before getting into the ranges, calculations, standards etc. I still don't get what the K-Factor is. The only thing I think I understand is that it is not what Adams said it was. When you read Adams you come away thinking it is just a safety factor built into the meter.

  5. #155
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    I'm not following. Did you mean to say a one stop flare factor? Let's assume the two exposures I listed are both 4 1/3 stops below metered and that the film density under zero flare conditions would arbitrarily be 0.20 above FB+f in either case. In the first exposure, the intensity of light entering the camera is high, and so some of this light (from the portion of the image circle beyond the borders of the emulsion) might bounce around, eventually bouncing onto the film and adding some additional exposure. At least I think it might. Maybe the actual film density ends up being 0.23 above FB+f. In the second exposure, a much lower intensity of light enters the camera, but the shutter is open for longer. Would we still expect a density of 0.23? Or would we actually get the zero flare density of 0.20 because the light intensity is not high enough to cause significant reflections in the camera - even though the film is exposed for longer.
    Same scene, same luminance range, and say shot at two different f/stops should have the same flare. And sorry about the "filter factor" typo. It was supposed to be flare factor.

    Perhaps there is no definite answer. Here's another way to think about the same example. You take a picture of a bright, uniform, featureless mid day sky and expose it to produce an expected net film D of 0.20. In the evening you take a picture of a middle grey, uniform, featureless evening sky and expose it to produce a net film D of 0.20 (so obviously this would be a significantly longer exposure than the picture of the mid day sky). Assume some camera flare in the first exposure leads to an actual net film D of 0.23. Would that occur in the second example too, even though the intensity of light entering the camera is lower? I'm thinking there would be less, or zero flare in the second exposure. Not sure.
    If the featureless sky takes up the entire frame, it's the same as shooting a target. It's virtually a flare free situation, or to put it more accurately, free of the effects of flare.

    Keep in mind this question concerns an in-camera film test with as little flare as possible (aside from some degree of lens flare which cannot be totally eliminated). The aim is to use a brightly lit white card for the entire series of exposures. In actuality, the lens is masked to restrict the projected image to within the borders of the emulsion. In other words, there should be no camera flare. But even though I would be using this mask anyway as an extra precaution, I'm wondering if it is necessary. So my example above would be the equivalent of not masking the lens.
    You're keeping stray light from entering the camera. The exposure of the white card shouldn't be affected either way. Even with an average luminance range the effects of flare at the point of the white card is inconsequential.

    Click image for larger version. 

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    Regarding the K-Factor discussion in Henry's book, as it happens I re-read that very section today, and I came away just as little understanding as when I first read the book. I wish he had started by explaining what the K-Factor actually is before getting into the ranges, calculations, standards etc. I still don't get what the K-Factor is. The only thing I think I understand is that it is not what Adams said it was. When you read Adams you come away thinking it is just a safety factor built into the meter.
    With Adams you come away thinking it's a conspiracy. You should read the stuff I wrote n the K-Factor thread. Here's a page.

    Click image for larger version. 

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    Henry talks about the various values of K, but he doesn't explain what it is or how it relates to exposure. In Henry's book you come away thinking it's an arbitrary decision by the manufacturer. BTW, he never really defines exposure (or from what I've read so far). I like that he has a bibliography, but he could take the level down a notch and include the titles of the papers. The book isn't for scientific publication.
    Last edited by Stephen Benskin; 01-26-2013 at 08:29 PM. Click to view previous post history.

  6. #156
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post

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    Michael R 1974,

    Yes Stephen made a tiny typo, he meant Flare factor.

    But look at this chart again. Now imagine doing a single-tone film speed test where you meter Zone V and stop down 4 stops (or 4 1/3 stop if you prefer).

    When you stop down, you move everything down.

    In the middle of the graph, Zone V, the meter point... you see the exposure+flare (realistic exposure) curve practically rejoins the theoretical exposure (45-degree theoretically perfect) curve. So a test exposure is not influenced much by flare.

  7. #157

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    I think I'm getting closer to really understanding this.

  8. #158
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    Quote Originally Posted by Michael R 1974 View Post
    I think I'm getting closer to really understanding this.
    You've got me doing some thinking.
    Last edited by Stephen Benskin; 01-27-2013 at 05:58 PM. Click to view previous post history.

  9. #159

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    Makes me feel a little better about repeatedly asking questions that should probably be basic. I appreciate you not giving up on my flare effect questions. Thanks to Bill also. I understand what non image forming light is, where it can come from, and it's effects on the characteristic curve. But I'm often less clear on assessing a specific situation (my in-camera/white card scenario for example). I'm prone to doing these sorts of "thought experiments" - call it scenario analysis - to see if I truly understand how to apply a concept. That is, can I look at a photographic situation and figure out if it is at least high or low flare. And actually I find film testing scenarios/setups more difficult to assess than most real photographic situations.

    The concept of flare is usually not taken that far in photographic texts (including Henry). I wish most texts went beyond the effects on the curve and gave some practical examples/scenarios. Then again, no information is probably better than bad information. The Book of Pyro, for example, contains some flare rules of thumb I'm not sure are accurate at all. As much as I am a fan of Adams, I think the subject of flare is a real shortcoming of The Negative. It is mentioned in little more than a cursory way, but can be a major source of distortion in Zone System testing and applications. It seems like something that should be given a full explanation even if we can't control it.

    Apologies again for pausing the thread on this particular variable.
    Last edited by Michael R 1974; 01-27-2013 at 07:08 PM. Click to view previous post history.

  10. #160
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    Quote Originally Posted by Michael R 1974 View Post
    As much as I am a fan of Adams, I think the subject of flare is a real shortcoming of The Negative. It is mentioned in little more than a cursory way, but can be a major source of distortion in Zone System testing and applications. It seems like something that should be given a full explanation even if we can't control it.
    Just my thoughts here, nothing critical. My views are geared more toward practicality, which the newcomer or first-timer parusing these threads must never, never, ever lose sight of, in the midst of all this theory.

    Your're right, it is not mentioned to any appreciative manner that even remotely resembles the type of discussions that occur here, yet his work speaks for itself, how important was it to him, I don't know, just asking. It begs the question, in my mind, as to just how important it really is in practical film testing for EI and N-times. It makes for discussion, and I do follow it, but just how important is it? This is not to imply that I think it has no affect, only that it's affect, has got to be so dependent on "degree" as to not warrant much consideration in the intellegent use of the Zone System.

    From The Negative, Appendix 1, regarding testing (I'm sure you've seen it, but it makes my point): "Choose a film and developer you use often, and be sure to use the same camera, shutter and lens throughout. Your exposure meter, lens diaphragm, shutter, and darkroom thermometer must be reliable----calibrated by a technician if possible. Once this "system" has been tested, any variations introduced by a change of equipment (such as the possible difference in aperture calibration or flare introduced by changing lenses) should be quite apparent if they are significant. For a change in film and/or development, of course, new tests must be conducted."

    So, essentially, flare, if significant, should be apparent with intelligent use of the ZS or any system and in that respect I fail to see any distortion in testing or application. I consider myself a competent ZS user and I simply have not been able to make a determination that flare is "apparent" in my "system", even though I'm fully aware that the tests I carry out (an in-camera contacted step tablet, exposed to Zone X to an evenly and diffusely illuminated single tone test target) are flare free. I make a decision before releasing the shutter as to what measure I may take to deal with possible flare influences, it is a negative by negative consideration and I rarely do anything different, and when I do, it is usually a -1/3 to -2/3 reduction in exposure. When compensating for it or not, the desired print is always obtainable as envisioned, flare has not seemed to affect the end result. If I had an older uncoated lens and switched from my new Nikkor to it, well then, it would be "apparent", even before exposure, that flare is going to affect my "placement".

    So I disagree with your statement, but given the spirit of the discussion I understand why you make it. In keeping with the OP, I would say to those wishing to carry out film tests for themselves for the first time, to just do it. Find a source i.e., BTZS, The Negative, Schaeffer, Lambrecht----follow it, and it only, to the "T" and be careful of outside advice, it is sure to trip you up. As one understands the concept of "expose for the shadows and develop for the highlights"----which the ZS and BTZS are simple vehicles toward that end, then one already has all they need to know to know how to deal with flare. At that juncture, flare in testing for EI becomes a mute point and you are assured that flare in actual photographing is intelligently dealt with.

    Just my opinion folks.



 

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