Tripod Use + Optical Viewfinder ?

[Yarin]

I've got a simple question:

When shooting from a tripod how important is it to cover up the viewfinder with the rubber cover to prevent light from entering and under(?)exposing a shot? I know that comparing covered to uncovered I see a difference of a few stops.

What what are the effects of not using this cover aside from light metering? From what I understand it seems as though letting extra light in through the viewfinder will underexpose a shot. Does the mirror flip up to prevent light from being captured by the CMOS sensor?

Just trying to understand a little more. Thanks

[Tapeman]

That depends on several factors. 1 length of exposure. 2 The amount and direction of light around the camera. 3 ISO setting? 4 If you can find that little rubber thing. When in doubt use it (one of the features I like on my 1v is a built in shutter on the eye piece.)

[Phil Hall]

Both the 1D and 1Ds have a lever to close off the light from the eyepiece. I have never noticed any difference and so hardly use them. If direct sunlight were shining into the eyepiece, there may be some difference.