Alley in Pisa, Italy

by Lars Kotthoff

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A rubber viewfinder cover is connected to my camera strap. What's it for, and when do I use it? What happens to a photo if I don't use it?

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I have been trying to figure out what that little rubber thing is for months! –  BBischof Dec 7 '10 at 6:41
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1 Answer 1

up vote 16 down vote accepted

The viewfinder cover is for when you take long exposures on a tripod. You only want light to come in via the lens, not through the viewfinder. Normally your eye covers the viewfinder and keeps stray light from entering the camera that way.

You really only need to use the viewfinder cover if there is bright light behind the camera. The mirror folds up and cover most of the prisma, so if there is as little light behind the camera as in front of it (as you are making a long exposure) it should not be a problem.

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Specifically, stray light coming in through the viewfinder can cause incorrect metering. –  Reid Jul 17 '10 at 2:37
    
there's a good way to visualize this. supposedly, you take a ~30 sec exposure with the lens cover on and point a light at the viewfinder...you get to see the damage it does to the photos. –  JoséNunoFerreira Mar 30 '12 at 15:35
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