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07-07-2010, 12:15 PM   #1
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grey card question

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I am trying to see how much to adjust my metering in manual mode when I meter off my hand. I am doing this by metering a grey card and then meter my palm to see how much ev compensation I should apply when metering off my palm.

So my question, I don't have a grey card....is it legit to meter off of an 18% grey from wikipedia on my computer screen? I am not sure if this is even accurate or not. I am trying to do this without having to go to the store or buy a grey card

07-07-2010, 12:18 PM   #2
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Is this even possible? I mean each monitor has different brightness and contrast. How can you tell how bright is the right setting? A quick dirt way I can think of is to spot meter off a piece of white paper, +2EV on the camera then you should have a rough guide.
07-07-2010, 12:25 PM   #3
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You're overthinking it a little.

In manual mode, and with center-weighted metering, I lock my metering on a part of the scene that I feel is closest to 18% grey, and then recompose.

It's not like I'm going to use an 18% grey card in the field, and after a while, you learn to identify 18% grey among the colors that you see.
07-07-2010, 12:55 PM   #4
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For the gray card metering to be meaningful, the gray card has to be reflective, and is in the same light as the object to be photographed.

The problems with the computer screen are (1) it's not reflective (it emits light thus you still can see it in the dark), and (2) it's unlikely to be in the same light as the object to be photographed.

Also, there is no magic in the 18% gray card. It just represents the reflectivity of an "average" scene. When the scene is not "average," e.g. a black cat, or a snowman, you'll need to make adjustments.

07-07-2010, 12:57 PM   #5
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I would hesitate about the computer screen.

grey card metering is about reflected light not light generated by a source. A 18% grey surface on the computer is too variable, aside from the screen's luminiscence, but also dependant on calibration of the screen.

Assuming the printer is calibrated, it may be better to print the image,

BUT

what I do, is I meter off something I think is about 18% grey, like a tree trunk, or paved roadway and set the metering with that.
07-07-2010, 06:35 PM   #6
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QuoteOriginally posted by trevorgrout Quote
Hi
I am trying to see how much to adjust my metering in manual mode when I meter off my hand. I am doing this by metering a grey card and then meter my palm to see how much ev compensation I should apply when metering off my palm.

So my question, I don't have a grey card....is it legit to meter off of an 18% grey from wikipedia on my computer screen? I am not sure if this is even accurate or not. I am trying to do this without having to go to the store or buy a grey card
Meter the palm of your hand and then +1.
Facing away from sun, clear blue sky = correct exposure.

Last edited by SpecialK; 07-08-2010 at 11:35 AM.
07-08-2010, 07:07 AM   #7
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You can also take a reading off of green grass or the blue sky away from the sun.
07-08-2010, 07:10 AM   #8
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QuoteOriginally posted by SpecialK Quote
Meter the palm of you hand and then +1.
Facing away from sun, clear blue sky = correct exposure.
That is exactly the method I have used for years. Palm in sun - +1; palm in shade - actual reading. When metering your palm in the sun make sure it is angled so you aren't metering glare.

07-08-2010, 11:06 AM   #9
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Note that metering the sky gives you an reading appropriate for a scene that is in full sun, but will be way underexposed for a scene that is *not* in full sun. The same is basically true of metering a grey card, of course - the reading is only valid if the scene you shoot is in the same light, so pay attention to whether you're in sun or shade. The difference between sun and shade varies from practically nonexistent on a mostly overcast day to more than 3 stops on a bright sunny days where the setting is such that the shade doesn't get much light from the sky (eg, a forest).

Last edited by Marc Sabatella; 07-09-2010 at 09:53 AM.
07-08-2010, 10:11 PM   #10
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Quick rules of thumb are great, however, Michael Freeman wrote a whole book (Perfect Exposure) about evaluating a scene compared to meter readings. Ansel Adams made his zone system famous and numerous books have been written about that. If you want to learn some variation of the zone system you can get to the point where you evaluate a scene against your meter and can come very close to spot on.
07-13-2010, 08:54 AM   #11
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Metering off your hand as a reference for a scene is making a BIG assumtion about a persons skin color.
07-13-2010, 10:50 AM   #12
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QuoteOriginally posted by tuco Quote
Metering off your hand as a reference for a scene is making a BIG assumtion about a persons skin color.
Yes. There is an assumption about the person's skin color.

But the assumption is not that big. The color of the palm (inside) does not vary from person to person as much as the back of the hand.
07-13-2010, 12:21 PM   #13
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QuoteOriginally posted by tuco Quote
Metering off your hand as a reference for a scene is making a BIG assumtion about a persons skin color.
It doesn't matter. If you meter off of your palm you are determining the correct exposure based on the EV of the scene. What is in the scene is irrelevant. It is no different than if you use a grey card or an incident light meter. Correct exposure is correct exposure.
07-13-2010, 12:46 PM   #14
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Read "Perfect Exposure" by Michael Freeman
07-13-2010, 12:46 PM   #15
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QuoteOriginally posted by tuco Quote
So if a scene has 15+ stops of light in it, what is the "correct" exposure when limit what you can capture is less?
This is not a fair question. You bring up the issue of dynamic range, which is not the point here. You'd face with the same problem no matter what method you use.

The point of Parallax's post (pardon me, Parallax, if I'm wrong in speaking for you) is that you use a constant surface (your palm) to measure light reflecting off it, overtime you will know how much to compensate to get "correct" exposure.

Even with the problem of dynamic range, you still can determine the "correct" exposure. Put your palm in the same light of whatever you want to capture, knowing other parts of the scene may be washed out or pitch dark, then measure of your palm, compensating as needed.
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