> I know F4 is F4. I also know that If I project a slide on a
> wall 5 feet
> away it is much brighter than if the wall is 20 feet away.
> Same amount
> of light spread out. Magnification does dim the image.
This is true if the focus screen itself was physically larger.
But since the focus screen remains fixed it doesn't matter what
the magnification of the viewfinder eyepiece is.
If you stand five feet away from that wall, is the image any
brighter than if you stand twenty feet away from the wall?
Take your slide, project it on the wall five feet away. Get out
your 35-70 zoom lens (or similar) and at the 35mm setting fill
your viewfinder with the entire slide. Take a meter reading.
Now, walk back and reframe at the 70mm setting. Meter again. It
should have EXACTLY the same exposure.
But it's about the size, isn't it? Well, rack the lens back out
to 35mm and spot meter the image. Should be about the same
exposure even though you now have a whole lot of black
surrounding the image.
But maybe this isn't a valid argument because we're talking
about macro. Well, that doesn't hold water either because you
can focus closer (hence get higher magnification) either by
extending the optics farther from the film plane or through
internal lens design (IF lenses). Nikon and Canon have nifty
telephoto/macro lenses which go down close to 1:2 with little
light loss, whereas my lenses achieve 1:2 through extension and
lots of light loss.
Remember, you are looking AT the focus screen, not through it.
(unless we're talking about the E10/E20). Viewing distance does
not alter light level.
AG
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