Question about Eyepiece Covers and their function

[LorenHa]

Hi guys,

First post on the forums :)

I just have a question regarding the eyepiece cover that's on my Canon strap for my XT.

For tripod night shots when I use a remote... I compose using the viewfinder (well duh, no liveview) and have my head there and focus and shoot with the remote, this blocks out stray light entering my camera and that's when the camera calculates exposure right, it doesn't need the blockage after the shutter is released? So do I really need the cover for these situations?
What about for AEB shooting when I want to do HDR? Do I need the eyepiece cover then because the camera readjusts exposure for each... exposure or is that all saved during the original shooting?

[iamaelephant]

To be honest I've never used the eyepiece cover, but then I haven't done a whole lot of night photography. I think it seems reasonable that if your head is very close to the viewfinder then not a lot of light will make it in. Regarding AEB, the metering for the whole sequence is done when the first shot is metered so stray light will not affect it. Even if this wasn't true, I doubt there would be enough stray light to affect the exposure in any case.

From my limited reading on the subject I think the cover is mostly useful for extremely long exposures (like greater than 60 seconds), in areas like astrophotography.

[neumanns]

Set your camera on M on a tripod...Adjust for proper exposer, Now move your head back and forth from the eyepiece and watch your exposure meter go wild.

Now assume your not in M on a tripod...if you do not block the eyepiece you meter calculates the exposure including the light coming in from the eyepiece.

The cover is for anytime your eye is not blocking light from entering the eyepiece....It can be much more and occasionaly less but it can easily throw your metering off by a full stop.

But only use it if you want a proper exposere (when your eye is not at the eyepiece)...If you don't care about a good exposure don't hassle with it.

Or you can lock exposure when it is covered....(I sometimes use my thumb)

[LorenHa]

So for a 30 second shot, it only matters if I cover the eyepiece when the camera meters? I don't have to cover it for the entire 30 seconds, if for example, I was lazy and wanted to use my thumb?

[iamaelephant]

No, stray light will still enter the eyepiece during exposure.

[neumanns]

I just use the thumb when I'm trying to compose and focus rather than putting the cover on and off. I shoot flowers a lot and I find it easier to cover with the thumb on short exposures.

[Jon]

No, stray light will still enter the eyepiece during exposure.
However the mirror will have flipped up; in order to affect the image, light would have to get past that. The metering cells are in the pentaprism area, so you need to shield them from stray light with the eyecup while an exposure's being calculated.