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  1. #31

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    In my opinion, there is no better discussion of reflected light metering vs. incident metering than will be found in the Phil Davis book, "Beyond the Zone System". Those who desire a comprehensive, but accessible, discussion of the nuances of both methods might avail themselves to the relevant materials. I would like to add that complicating the issues involved in metering is the fact that, as the late Mr. Davis so elegantly wrote, the "meter cell assumes that the world is bathed in a 5-stop range of uniform, shadowless light, but the calculating dial....assumes that the cell's readings relate to the real world where shade and shadows are ever-present and where 7 stops is the norm". He goes on to point out that there is a discrepancy in "what the cells measures and what the dial does with those measurements"...what follows is a simply way to determine the SBR of a scene, and how to use such information to achieve the "correct" development of one's film ( based upon previous tests of one's own materials ). Mr. Davis does take pains to point out that BOTH metering methods have application and relevance, but both must be used with understanding and insight.

    The quick solution to the conundrum raised by Mr. Porter ( as described by Mr. Davis ) is to decrease the exposure by one stop if one has only a shadow reading, and increase the exposure by one stop if one has only a single highlight reading.

  2. #32
    Lee L's Avatar
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    Quote Originally Posted by markbarendt View Post
    On occasion, when using my Nikons, I will walk up to my subject then turn back toward my camera position and meter the scene with the camera or the sky in that direction. In this case I'm using my cameras "reflective meter" as an "incident meter."
    No, to claim that this is an incident reading is to completely misrepresent what in incident reading is. This method is using the camera in reflective reading mode to read the correct exposure for the scene you're pointing at. An incident reading detects the amount of light falling on the subject, not the amount of light reflected from the camera position as seen from the subject, which is what you're describing. To achieve an actual incident reading with the camera in this way, you need something like an Expo-Disc over the end of your lens to get a proper incident reading. It needs to emulate a gray card through reduced light transmission and proper color balance.

    You also need to watch yourself and test with the matrix metering Nikons (and similar) and an Expo-Disc because they bias exposure based on light levels and contrast, so they may not do that well at low or high light levels using an Expo-Disc. Using spot or center weighted averaging mode with an Expo-Disc should be more accurate than matrix-metering.

    Lee
    Last edited by Lee L; 02-07-2010 at 12:00 PM. Click to view previous post history.

  3. #33
    Lee L's Avatar
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    Agree wholeheartedly with Mahler-one's take on Phil Davis' incident metering methods. Well worth reading just to understand the proper usage of incident meters, even if you don't use Davis' incident zone system.

    Lee

  4. #34
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    Quote Originally Posted by CPorter View Post
    Taking an incident reading in the sun and then the shade could have been done and then expose for the average reading. That would probably be the better use of an incident meter IMO, since it does take into account acutal reflective values at both the dark and the light end of the range.
    Another point for clarity.

    CPorter illustrates a great point here in that it takes judgment to use any meter properly.

    BUT, incident metering NEVER, NEVER, NEVER, takes into consideration the reflectivity of the surface.

    Plain and simple, the meter can't even see the reflective surface because it is BEHIND the meter.

    I'm not saying CPorter's method is not workable, just different.

    CPorter's point is essentially about defining your exposure placement based on what is important to you.

    What is important to you depends on what's next. An example from my world.

    In the situation CPorter presents I would use my incident meter unshaded a foot or two from the wall, pointing the meter's dome at the camera and set the camera with that reading because the setting the meter would suggest there would place that middle gray sat dish exactly in the middle of the exposure.

    So what's next?

    This negative, for say Delta 400, would give me easily about 4-stops of detail on either side of middle gray with the normal manufacturer's recommended development times, temps, and agitation.

    Well I'm not normal except with temperature and I've tested my stuff and tailored my own process to get results I like better.

    To insure I get good shadow detail in shots like this my development time is what others might consider proper for N+1 or a one stop push.

    To protect the highlights and avoid over-development I reduce my agitation considerably. With Xtol that means 1 inversion every 2 minutes instead of 5-7 every 30 seconds.

    What's after that?

    The enlarger and I just didn't get this next point until I got an enlarger. It is why film is soooo flexible.

    I get to make a tailor and control a whole new exposure specifically to get the very best from that negative onto paper.
    Mark Barendt, Beaverton, OR

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

  5. #35
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    Quote Originally Posted by Lee L View Post
    No, to claim that this is an incident reading is to completely misrepresent what in incident reading is. This method is using the camera in reflective reading mode to read the correct exposure for the scene you're pointing at. An incident reading detects the amount of light falling on the subject, not the amount of light reflected from the camera position as seen from the subject, which is what you're describing. To achieve an actual incident reading with the camera in this way, you need something like an Expo-Disc over the end of your lens to get a proper incident reading. It needs to emulate a gray card through reduced light transmission and proper color balance.
    My point for that post was that if you want an incident measurement you have to measure the light falling on the subject not the light at the camera position.

    Your Expo disk suggestion is great BTW, as a quick and dirty emulation of that I defocus as far as possible.

    Quote Originally Posted by Lee L View Post
    You also need to watch yourself and test with the matrix metering Nikons (and similar) and an Expo-Disc because they bias exposure based on light levels and contrast, so they may not do that well at low or high light levels using an Expo-Disc. Using spot or center weighted averaging mode with an Expo-Disc should be more accurate than matrix-metering.

    Lee
    You are absolutely right with your caveats here, this technique takes real thought and a grain-of-salt.
    Mark Barendt, Beaverton, OR

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

  6. #36
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    Quote Originally Posted by markbarendt View Post
    In the situation CPorter presents I would use my incident meter unshaded a foot or two from the wall, pointing the meter's dome at the camera
    What? That's exactly what I did!

    I placed the dome in the shade of the dish while pointing the dome toward the camera. And I placed the dome in the sunlight in front of the wall while pointing the dome toward the camera.

    You somehow think that I pointed the meter's dome toward the wall in that example?

    When I said "incident reading taken here", it means just that, an incident reading.

  7. #37
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    Quote Originally Posted by CPorter View Post
    These are not real good negative scans but the point is conveyed---some examples of this point about incident metering.

    There is obviously more light than dark in this subject. But when composing the third shot, I made sure the center-weighted meter of the camera was influenced more by the dark shaded area. The meter's outer, less sensitive regions were also a factor in determining the exposure, just not as much, but ultimately gave a more satisfying result.

    Taking an incident reading in the sun and then the shade could have been done and then expose for the average reading. That would probably be the better use of an incident meter IMO, since it does take into account acutal reflective values at both the dark and the light end of the range. It actually attempts an average exposure rather than letting the reflective meter alone try and average the scene, which can lead to some pretty poor exposures if the scene is nowhere near average.
    On the third shot, if you had taken an incidence reading agint the siding and then in the shadow behind the dish would the average have been the same as the third, center weighted shot?
    "Generalizations are made because they are generally true"
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  8. #38
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    Quote Originally Posted by CPorter View Post
    What? That's exactly what I did!
    I was not trying to suggest anything otherwise, just trying to keep my thoughts clear.
    Mark Barendt, Beaverton, OR

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

  9. #39
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    Quote Originally Posted by stradibarrius View Post
    On the third shot, if you had taken an incidence reading agint the siding and then in the shadow behind the dish would the average have been the same as the third, center weighted shot?
    Did you say you had a Gossen Luna Pro? Set it to 1/250 at f8 and you'll see there are three stops between the shadowed reading and the sunlight reading.

    The shadow reading was 1/250 at f8 and the sunlight reading was 1/250 at f22. Taking the exact average would be 1/250 at and halfway between f11 and f16 on the dial. So, I guess on my Canon Rebel X, I would have set the average at 1/250 at f13, pretty close. This would have given just a bit more exposure to both the shadow and sunlit area.

    It should be kept in mind though, that this is a very simple scene with basically two main reflective surfaces. Using the incident meter to average the high and the low light levels, while I think is a good way to use it, still does not give you an idea of the many reflective surfaces that makes up most scenes. In that respect, the spot meter is the best tool IMO, to zonies like myself, it affords the greatest amount of control. To others into the BTZS system, the incident meter is the tool of choice I believe.

  10. #40
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    Quote Originally Posted by markbarendt View Post
    Point for clarity here.

    When any meter is pointed at the subject from the camera position, even an incident meter, it is being used to measure reflected light.

    To measure incidental light any meter must be in the same light as the subject and be pointed at the camera position.
    Yes. With the adaptor on the Kodak, you move the camera to the subject and point it at the camera position (the position of the camera before you moved it to take the reading!).


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

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