Telephoto lens makes things look brighter

Sitting in my living room playing with all of this equipment, I've noticed something that I need explained.

I'm shooting the upper right corner of my living room which is paneled in dark paneling and there is no light there. When I shoot with the EF 24-85mm f/3.5-4.5 USM lens on the 20D in P mode and no flash, it's pretty dark. Much like it is when I look at it.

When I shoot with the EF 70-200mm f/2.8L IS USM, it looks like it's freakin daylight over there in the dark corner.

Why is that?

Thank you.

Cliff

It is possible that the 24-85mm is underexposing the image. Another possibility is that the camera is using evaluative metering and so it's getting an overall meter of the area and choosing the correct exposure. The 24-85mm might include more areas that are lighter, tending to underexpose the corner whereas the telephoto has the advantage of filling the frame with the corner with fewer light spots, giving a better exposure. Try reshooting in manual using the exact same settings with each lens at (preferably) the same focal length and you then should get similar results.
Cheers,
Reed

An f/2.8 lens will always make the image look brighter in the viewfinder as opposed to a slower lens. I noticed that when using two bodies for baseball. The camera with the 200L had a brighter viewfinder image than the other body with the f/4 zoom.

When you say 'brighter', Are you talking about what you see in the viewfinder, or the RAW or JPEG images recorded by the camera ?

Theoretically, there shouldn't be a difference. The camera should be finding the proper exposure for you in all modes except for full (M)anual.. Then it's up to you.

Can you post example images with the EXIF info included ?

On the viewfinder. The image on the viewfinder looks brighter when using the telephoto lens.

As liza said above, you are looking through an aperture of f/2.8 with the telephoto and an aperture of f/3.5-4.5 with the 24-85. You are getting less than half the light coming through the 24-85 depending on the focal length you are using.

You should see how nice and bright every thing is looking through the viewfinder through an 85/f1.2L. As compared to my old 28-135/f3.5-5.6.

Remember that when looking through the viewfinder the aperture is at it most open so the most light is being let in. So a bigger aperture (smaller number) is letting in more light.

When you go to take the picture is when the camera stops down the aperture to whatever you or the camera (if in auto modes) have it at to take the picture. But until then it is wide open.