Westminster fountain at sunset

by Jorge Córdoba

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I know that a real gray card is the best thing to use to determine exposure. But I'd like to know if there are other naturally available features that can be used in a quick and dirty way. Are fields of grass or road tarmac appropriate?

The reason for asking is that I suspect that my new used (manual focus) lens is exposing incorrectly using my camera body. I don't have access to a gray card, but I do have access to lawns and pavements, nicely and evenly lit by a cloudy sky.

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Is the 'manual focus' lens also one with only manual aperture? –  Dreamager May 28 '11 at 13:02
    
@Dreamager: yes, it's actually 2 newly purchased Nikkor lenses from the late 60s, early 70s. Both have been "AI'd" and I set the aperture on the lens. –  gerikson May 28 '11 at 13:07

5 Answers 5

up vote 6 down vote accepted

Grass is generally considered to be 18% grey. I would guess if you shoot in grey scale mode and your exposure is said to be correct, it should come up 18% grey.

There's also the sunny 16 rule, which is on a sunny day, shoot at 1/ISO shutter speed, f16. This should produce a correctly exposed picture. You can check to see if this results in a correct picture.

Both of these were tricks I was taught back in film days.

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Thanks, I would probably have remembered the Sunny 16 rule if it had been, in fact, sunny ;) –  gerikson May 28 '11 at 14:45
    
There's also the lesser-known "Overcast 11" rule, which has a much less catchy name. In general, mid-day light is pretty constant and if you're not dealing with shadows or changing weather, you can tweak your exposure manually and leave it there for a while. –  Evan Krall May 28 '11 at 18:41
    
+1 grass and blue sky (away from the sun) should be close. –  MikeW Feb 29 '12 at 4:50

Do you have a camera bag? A lot of them have a gray interior that's fairly close to what you're looking for, especially if you have dividers you can pull out and use by themself. You may have to tweak the final balance, but it will be in range.

An another approach is to DIY it on a printer. Again, it won't be perfect, but it would be close enough for basic testing to eyeball any adjustments afterwards. If you go this route, in a decent editor, fill an image with 18% gray and then print it. A good photo printer is probably better than a laser, but don't use high gloss paper, it should be mat.

Plain white paper can also be used. This will not be gray, of course, but is a known white. Using that, you can adjust until it is white and then everything else should be balanced.

By the way, shoot raw so that you can make adjustments after the fact.

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This does not seem to answer the question. OP seems to be interested in getting the exposure correct, not the white-balance. –  Jukka Suomela May 28 '11 at 14:25
    
Thanks for the camera bag interior tip, I do have a Domke bag which I would be surprised if it's NOT 18% gray ;) In any case I can compare to a known "good" lens. –  gerikson May 28 '11 at 14:44
    
@Jukka - He asked for alternatives to gray cards, I gave him those... –  John Cavan May 28 '11 at 14:53

Grass (or other leaves), a clear, blue sky, or the palm of your hand -- but it does need to be the palm, not the back or other parts of your skin. Other parts have pigmentation that varies the color, but palms have (almost) no pigmentation.

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You could try using The Zone System if you have objects in your scene that you can relate to a specific zone.

For example, you could use a white piece of paper or a bright cloud (zone 7), and use a +2 exposure compensation, to make sure it remains white. Or you could use

clear north sky; dark skin, average weathered wood

to get a good exposure without exposure compensation.

Just take a look at the Zones as tone and texture section on the Wikipedia page.

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If at any time you do have access to a gray card, meter it, and also meter the palm of your hand. Note the difference: for example, let's say your hand meters 1/2 stop higher than the gray card.

In the future, as long as you have your hand with you, you'll be able to meter it and adjust your exposure by that 1/2 stop.

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