18% gray

Can anyone explain the significance of 18% gray? Where did it come from and why is it the standard in metering for photography? I've read about how to read for 18% gray, but I can't make it work, if I don't understand it... *smile*

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Originally Posted by darkrainfall

Can anyone explain the significance of 18% gray? Where did it come from and why is it the standard in metering for photography? I've read about how to read for 18% gray, but I can't make it work, if I don't understand it... *smile*

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This is a mid tone gray. It's halfway between white and black. I don't know where the 18% comes from.

The basic idea is that the average scene adds up to an overall midtone. The key is knowing when it doesn't and how to compensate. Or, using it to insure the part of the scene you want to be a midtone is.

The color doesn't have to be gray, it just need to be a midtone color. Green grass for example, works well.

Mike

18% gray is what your camera's reflected light meter sees as a middle exposure, not over, not under. If you were to point your camera at at 18% gray, or anything else that reflects the same amount of light for that matter, your camera's meter would show a "correct" exposure for the light that you are in.

Most normal scenes are said to reflect 18% when everything in averaged out. The problem comes in dark and light subjects.

If you shoot a white scene, the camera thinks it's bright not white. So it will underexpose the scene in an attempt to make it closer to 18% gray. Conversely, if you are shooting a black subject, the camera thinks it's dark, low light, not dark as in color. So the camera will overexpose trying to make it closer to 18% gray.

To use a gray card, hold it in the same light you are going to shoot the subject. Note the setting, that is the "correct" exposure for that light. Now regardless of what you shoot as long as it's in that light use the settings given when metering the gray card.

Hope that helps,

Dennis

Oh!! I understand now! *smile* I've been taking pics for quite a while and until now I just never quite understood what was so special about 18% gray. Thanks. *more smiles*

First of all, Tiffany, to clear up your original question, an 18% gray card is called that because it reflects 18% of the light that hits it.

As the other replies here have already mentioned, the card makes a very good metering reference as reflective light meters are calibrated for this gray tone. Still, using the card alone works best only when the overall scene illumination is balanced and average.

The other thing you need to be aware of in a scene is the brightness RANGE, also (as darkman points out) where the tones of the MOST IMPORTANT areas of a shot lie.

These important areas may be getting more or less light than the gray card would indicate. IOW, important areas of a shot may be in dark shadow or bright sunlight. If that's the case, you would use the gray card reading as a STARTING POINT, and make adjustments on your exposure to insure the correct exposure for the other areas.

BTW, these are the basic principals of the ZONE SYSTEM, developed by Ansel Adams as a very precise way of determining film exposure and print development. Do a GOOGLE search to find online resources explaining this in more detail...

One important thing to be aware of if you're shooting digital, is that digital capture actually behaves more like SLIDE film as opposed to NEGATIVE film. So, you always need to be aware of the highlight details and exposure.

If you overexpose a digital image and blow out the hightlights, you cannot get this information back. So I guess my point is it's fine to use a gray card to get a ballpark exposure reading, but make sure your highlights are not being vastly overexposed, unless of course, you're positive you want them that way.

BTW2, don't know if you're aware of it or not, but on your web site, the images on your STOCK page don't load...

Quote:

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Originally Posted by darkrainfall

Can anyone explain the significance of 18% gray? Where did it come from and why is it the standard in metering for photography? I've read about how to read for 18% gray, but I can't make it work, if I don't understand it... *smile*

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Quote:

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Originally Posted by darkrainfall

Can anyone explain the significance of 18% gray? Where did it come from and why is it the standard in metering for photography? I've read about how to read for 18% gray, but I can't make it work, if I don't understand it... *smile*

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18% Gray or Midtone<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>

<o:p></o:p>

Geometric Average of all Reflectance Values<o:p></o:p>

Minimum Reflectance - Black - 3.5%<o:p></o:p>

Maximum Reflectance - White - 92.5%<o:p></o:p>

Average = The Square Root of (3.5 x 92.5) = 18

This is Approximate

hi Steve, is that work the same way if you were shooting in door with the external flash though?

Wrong Steve :) but grey cards are for use with existing light only, not flash. Flash exposure is a whole different world. Tell you what - if you've got some questions about that, start a new thread on it and we'll be glad to help.

oop...so sorry, didn't mean to be rude but I thought it would be similar thread so I just come in and ask. I m still in the process of learning.

No problem, but exposure can be a tricky subject. Flash exposure is so different from ambient light exposure that I think it would really be a lot easier to follow if it was under a separate thread, that's all.

kool, I just want yall all to know that I love this website. It help me alot, my wife toll me why Im in here all the time when not working, not just to post but read all the question and anwers its all greats learning experience...yall all wonderfull