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  1. #51
    markbarendt's Avatar
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    Quote Originally Posted by zumbido View Post
    I'm an amateur, but...

    The subject is three-dimensional. So some choice has to be made about not just "the light falling on the subject", but the light falling on certain parts of the subject. Sometimes the subject will be lit evenly but that's rare unless you specifically set out to do so (and do it well). If there's a streetlamp reflecting off a newspaper box and illuminating my subject's rear while I'm taking a picture of their face from the bust up, my "incident" reading will be a lot more useful if it takes into account the light falling on the subject that will actually be in the frame.

    Is that wrong? I realize that semantically this makes it maybe more a consideration of "reflection", in a sense, but... at a fundamental level reflected light is the only thing that matters, since it's the only thing we see. Or not?
    It is not wrong to consider all the tones.

    In the end though you have to pick one setting for the camera.

    Using your example with an incident meter and a reading taken at your subjects nose the meter would automatically place:

    Caucasian skin a stop or so brighter than middle gray, which is normal.

    Dark hair will be darker than middle gray.

    A white shirt in the same light should be white, black shirt, black, blah, blah, blah.

    Incident meters are great for finding the normal exposure.

    Context is important though.

    If you are shooting in a situation where you want the subject's face to be darker than normal, say under a street lamp at night for mood, you would just stop down some. This would be an artistic adjustment to a technically perfect reading.
    Mark Barendt, Beaverton, OR

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

  2. #52

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    Quote Originally Posted by Q.G. View Post
    Not quite true.

    We usually want to have the bit the camera sees, the bit that will be captured on film, to be exposed the way we want it. Who cares about the parts of the subject we don't see?

    So where the camera lens is relative to the subject does indeed matter. It determines what parts of the subject will be on film, which will not.

    They don't say those things for nothing, you know.
    That the metered areas falls within the frame is a given. That you meter for the light falling on a part of the subject that is seen by the lens is also a given.

    Nonetheless, I almost disclaimed anyhow, just because I knew someone would say something. I just got lazy, I guess.

    Also, I simply said "where the camera lens is", not "where the camera lens is relative to the subject". What I meant was that when metering, seeking out the location of the lens for something at which to point your meter is a method that does not make sense at all, technically.

    It is really as simple as: Point the meter at the light you want to measure.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  3. #53
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    Quote Originally Posted by 2F/2F View Post
    This is why I say that the contrastier the light on the subject, the more important it becomes to meter the main light source instead of the "down the middle" average, which is what you get by pointing the thing at the camera all the time.
    All good points you made.

    Averaging could be done without just pointing it at the camera-----it could also be done by taking the reading on the main light source side and then the shadowed side, either way, in natural light when sun and shadow is the case, an averaged reading would seem to afford the best negative, IMO, coupled with wise development.

  4. #54

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    Why would an averaged reading make the best negative? A shot metered for the main light would be correctly exposed, and a shot metered for the average would be overexposed. Which of the two is best?

    Now, if you are talking about purposeful overexposure on negative film (for one or more of the many reasons one might have to do this), that is a special circumstance, and should not be used to guide standard working procedures. Overexposure and altered development is something you'd do to change the contrast of your film, not something you would do in all occasions.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  5. #55

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    Quote Originally Posted by 2F/2F View Post
    What I meant was that when metering, seeking out the location of the lens for something at which to point your meter is a method that does not make sense at all, technically.
    Well, no. That's the point. It does indeed make a lot of sense.

    Quote Originally Posted by 2F/2F View Post
    It is really as simple as: Point the meter at the light you want to measure.
    I wholeheartedly agree.
    The light you want to measure is the light that is illuminating the bits that will be captured on film. The bits your camera lens is seeing.

    See how it makes sense?

    But it is a general rule, and needs to be adapted - fine tuned - for specific situations. Still makes sense even then though.

  6. #56

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    Quote Originally Posted by zumbido View Post
    But wouldn't a corollary be that the light falling on the subject from the direction the camera is viewing is very likely to be the light we want to meter for? Since, after all, that's the light that we'll be viewing the subject in for the photograph.
    As I said, this is true in low-contrast light, and the more contrasty the light, the less it is true. However, when it is true, it is not true because the meter is pointed at the camera lens. It is true only because in that particular lighting situation, pointing the meter at the camera lens will give the same reading as pointing the meter any other direction. This is why I say the location of the lens doesn't matter, but where the light is coming from matters. Your meter doesn't know what a camera lens is. It only knows what light is.

    The "at the camera" method is a rule of thumb that will get printable exposures on negative film. It is exactly the kind of method that instruction books are full of, but that anyone who is teaching more detailed and technically correct methods would not recommend.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  7. #57

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    Quote Originally Posted by 2F/2F View Post
    As I said, this is true in low-contrast light, and the more contrasty the light, the less it is true.
    Yes and no.

    They use a dome for incident light metering. Not a flat surfaced diffusor.
    That integrating dome, admitting light from a 180 degree angle, will 'see' the contrast.
    So you get an averaged result automatically, when pointing the dome at the camera lens.

    Quote Originally Posted by 2F/2F View Post
    The "at the camera" method is a rule of thumb that will get printable exposures on negative film. It is exactly the kind of method that instruction books are full of, but that anyone who is teaching more detailed and technically correct methods would not recommend.
    They certainly would. Because it is a sound, valid method.

    They would also talk about fine tuning the method.
    That fine tuning involves deciding what you want to have exposed in what way. Decisions that also determine what you meter.
    Which, by the way, is the same for any metering method.

  8. #58
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    I'm not inclined to answer point-by-point, but here are some factors to consider.

    Very few reflecting surfaces in the real world have either perfectly specular or lambertian reflective qualities. I.e. they don't reflect like a mirror nor do they perfectly diffuse the light striking them over 2 pi steradians. Most surfaces reflect more strongly back toward the light source and more weakly at angles off that axis. So measuring the light striking an object from 90 relative to the camera position is not measuring the amount of light reflected from that object toward the camera. Therefore a measurement taken with an incident dome pointed at a light source 90 degrees from the camera will underexpose to varying degrees, depending on the reflective qualities of the object being photographed.

    With the light meter dome at the subject pointed toward the camera, light from a source at 90 degrees from the camera axis will light half the translucent dome directly, and any light reflected by nearby objects will fill in on the rest of the incident dome. Once the direct light and reflected light enter the incident dome, it will scatter and reflect off the interior surface of the meter dome and back to the sensor cell, so the dome is self-compensating mixing box that sees both the direct and reflected light falling on it. It's designed to be a self-compensating system with the dome pointed at the camera.

    The dome on an incident meter used for 3-D subjects is three dimensional, and by design acts to account for the action of light reflecting off a 3-D object when the dome is pointed toward the camera. For shooting flat art copy work, incident meter manufacturers often supply a flat incident diffuser to simulate a flat surface. For the same reasons of specular/lambertian properties in the object being photographed as mentioned earlier, the flat incident meter diffuser does a better job of simulating the way light reflects from a flat object. Flat diffusers are also very handy for determining lighting ratios in the studio with more than one effective light source (two or more lights, or light + reflectors).

    The reason that you keep seeing the instructions to point the incident meter dome at the camera repeated everywhere is because it is designed to work that way. The meter dome should be placed to account for all of the light that a three dimensional object can possibly reflect toward the camera. If you point the incident meter dome directly at a light source that is 90 degrees from the camera, a large percentage of the light you're measuring can't possibly be reflected toward the camera by a 3D object that's entirely within the field of view of the camera, and you're not metering the reflected light from opposite the main light source that can be reflected back toward the camera.

    Lee

  9. #59

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    Quote Originally Posted by Q.G. View Post
    Well, no. That's the point. It does indeed make a lot of sense.



    I wholeheartedly agree.
    The light you want to measure is the light that is illuminating the bits that will be captured on film. The bits your camera lens is seeing.

    See how it makes sense?

    But it is a general rule, and needs to be adapted - fine tuned - for specific situations. Still makes sense even then though.
    I see what you are saying, of course...but I would say it this way: In general, the direction you point the incident meter will be well within 90 degrees of being pointed right at your camera lens.

    However, there are a few situations in which the light you want to measure is not always the light that is illuminating what is captured on film.

    In all situations, however, the light you should measure for deciding exposure is the light for which you want to expose.

    Sometimes that will be the light that is falling on a part of your subject that does not appear on the film (is not "seen" by the lens).

    The most obvious example is when you have a primarily backlit person and want to expose for the background instead of the person; a classic silhouette.

    Another time I would meter with the dome more than 90 degrees from the camera lens would be simply to get a background reading to see how many stops away from the foreground reading it was. I do this all the time.

    ...and yes, the flat disc is the better tool for this...but the dome works this way just fine.

    ...and no, no instructor whose technical expertise I respect has ever taught me to point the dome at the camera. They have taught me specifically not to do so (obviously).
    Last edited by 2F/2F; 02-07-2010 at 03:25 PM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  10. #60

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    Quote Originally Posted by Steve Smith View Post
    It's not common, especially now, but my Kodak Retina Reflex cameras are fitted with Gossen meters. They came with plastic diffusers to clip on the front to take incident readings.


    Steve.
    That reminds me. My Retina 3c has a built-in meter attachment for incident readings, as does my Rolleiflex T. Both meters are made by gossen and both attachments are a plastic diffuser that snaps over the meter cell.
    Rick Jason.
    "I'm still developing"



 

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