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  1. #1

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    I don't think I understand incident metering after all

    So I was out in the field yesterday shooting, and I was messing around with both incident and reflective metering. My understanding is that, if I point the meter in reflective mode at an 18% grey card, and then take an incident reading in the same lighting, I should get the same reading.

    However, it just doesn't seem to work that way: almost invariably, when I feel like I'm pointing the reflective meter at an "average" scene, putting the dome on in the same lighting drops the reading (i.e., calls for more exposure) by one to two stops.

    I can think of three explanations:
    1) my estimate of "average" is one to two stops off;
    2) something is peculiar about my meter, causing either me to operate it wrong or it to read wrong; or
    3) I don't understand how incident metering works after all.

    The meter is a Luna-Pro SBC and I'm pretty sure it's in good repair---it's served me admirably as a reflective meter. So I think something is wrong with me, be it in my sense of what makes a "correct" reflective reading (#1), operating my meter (#2), or understanding the whole point (#3). Help?

    -NT
    Nathan Tenny
    San Diego, CA, USA

    The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
    -The Little Technical Library, _Developing, Printing, And Enlarging_

  2. #2
    2F/2F's Avatar
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    It is simple if you think about it like this: Reflected meters place whatever they are pointed at as a middle gray. Incident meters place middle gray as middle gray. That means that dark things end up dark, middle-toned things end up middle toned, and light things end up light. With a reflected meter, whatever it is pointed at ends up as a middle tone, regardless of how dark or light it is in reality.

    The dome needs to be pointed at the right thing, of course.

    And no; assuming the same value is used for middle gray with both meters, a gray card reading should not match an incident reading. You should have to open up 1/2 to 2/3 of a stop from a gray card reading to match an incident reading. And the gray card takes the place of the dome, so should be placed where you would place the dome.

    Assuming both meters are calibrated properly, I would trust the incident. It is far more likely that the reflected meter is telling you to underexpose than it is likely that the incident meter is telling you to overexpose.
    Last edited by 2F/2F; 07-23-2011 at 06:51 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."

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  3. #3
    David A. Goldfarb's Avatar
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    First off, are you pointing the dome in the right direction, which is the opposite of the direction for taking the reflective reading without the dome? In other words, the same light falling on the grey card should be falling on the dome for making an incident reading.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
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    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  4. #4
    Rick A's Avatar
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    Hmm... Lets see, when you take a reflective reading, you must decide which zone you want that reading to be in, and set as necessary. You may want to take several readings and average then to get shadows and highlites to both be included as much as possible. You can also take readings of thnge that are similar in reflectance to a gray card and use that setting.

    When you take an incident reading, you stand in front of the subject and point the light dome toward the camera lens, and thats the setting you will use. If it isn't convenient to do that, place the meter in approximatly same lighting and take a reading. If your main subject is in shadow, creat a shadow that resembles the one surrounding subject and take the reading. It really doesn't get any easier than that.

    Anyway, thats how I do it.
    Rick A
    Argentum aevum
    BTW: the big kid in my avatar is my hero, my son, who proudly serves us in the Navy. "SALUTE"

  5. #5
    2F/2F's Avatar
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    I would add that you don't have to use the reading on the incident meter to make the shot. If you know that the scene is high in brightness range, and you want to fit it onto your printing paper more easily, you can overexpose and underdevelop. You can also do the opposite in the opposite situation. With an incident meter, you will get best results if you pay close attention to brightness range and make these changes as needed. So, they are not completely idiot proof...but definitely much more so than reflected meters.
    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)

  6. #6

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    My guess is that you pointed the meter in the wrong direction when making the incident readings. Your 1 to 2 stops less light than a reflective reading tells me that.

  7. #7

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    Quote Originally Posted by 2F/2F View Post
    The dome needs to be pointed at the right thing, of course.
    I'm uncertain whether this means "towards the camera" or "towards the sky" (in outdoor full sun)---I can see an argument for both. In this setting it didn't make too much difference; the sun was *extremely* bright ("sunny 22" conditions) and there was a lot of reflection from a light-colored landscape, so as long as I didn't throw an actual shadow on the dome I got pretty consistent readings in all directions.

    And no; assuming the same value is used for middle gray with both meters, a gray card reading should not match an incident reading. You should have to open up 1/2 to 2/3 of a stop from a gray card reading to match an incident reading.
    I don't understand this part. Isn't the idea that the dome looks to the meter like a gray card?

    Thanks

    -NT
    Nathan Tenny
    San Diego, CA, USA

    The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
    -The Little Technical Library, _Developing, Printing, And Enlarging_

  8. #8
    Rick A's Avatar
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    You point the dome at the camera lens for an incident reading.
    Rick A
    Argentum aevum
    BTW: the big kid in my avatar is my hero, my son, who proudly serves us in the Navy. "SALUTE"

  9. #9
    2F/2F's Avatar
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    Quote Originally Posted by ntenny View Post
    I'm uncertain whether this means "towards the camera" or "towards the sky" (in outdoor full sun)---I can see an argument for both. In this setting it didn't make too much difference; the sun was *extremely* bright ("sunny 22" conditions) and there was a lot of reflection from a light-colored landscape, so as long as I didn't throw an actual shadow on the dome I got pretty consistent readings in all directions.



    I don't understand this part. Isn't the idea that the dome looks to the meter like a gray card?

    Thanks

    -NT
    This is a can of worms. Not sure if you really want the discussion going on in this post. Check the archives. Points have recently been made arguing a variety of methods.

    The skinny of it: The worst you can do by always pointing the dome at the camera is to overexpose in cases in which the lighting is uneven. Most people do not notice this with negative film. But it definitely happens, and can be fatal to the shot with transparency film.

    Personally, in ratio lighting in which I want to preserve the ratio as lit, I always point the dome at the source of light for the brighter side of the subject.
    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. #10

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    Here's my understanding, and my reading agrees with this method.

    Let's say you have a camera and you are pointing your camera at a gray card at some distance.
    1) Set your meter at reflective mode. Stand at where your camera is, and point your meter to the gray card.
    2) Set your meter at incident mode. Stand at where your gray card is, and point your meter to the camera.

    You should get the same reading. When you do this, be VERY careful your own shadow does not obscure the sensor on the meter. I am also assuming you have a SPOT meter with just enough coverage to JUST read your gray card. If it reads more, your bets are off. You'll have to get closer to the card.
    Develop, stop, fix.... wait.... where's my film?

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