> Using DOF preview stop from f/1.4 to f/1.8. Is there is no change in the
> viewfinder brightness, there is mirror vigneting at f/1.4. If the
> brigntness change from f/1.4 to f/1.8, then there is no mirror vigneting.
>
> As it depends on the body, the effect can be quite different from body to
> body.
> I will not be surprised to know that the vigneting effect I see on my EOS
> 500n is not present on a EOS 3.
>
> As a conclusion I'm pretty sure that in my EOS 500n the efective aperture
> as seen from the focusing screen is less that the one seen from the film.
> But I'm not sure of the importance of it's effect on DOF. But In my
camera,
> using a EF 50mm f/1.8 I, the DOF on the focusing screen at f/1.8 must be
> greater, perhaps slightly only, than on film.
>
> Hope it helps.
>
> Best regards
>
> Vicente
I haven't had a 1.4 lens on my EOS yet, but I remember using my old Minolta
SRT 101 with 58mm 1.4 I could definitely see DOF preview change from 1.4 to
2. That is to say, the finder got darker a little bit. And I'm positive that
mirror was way less than 100 percent coverage.
Having said that, I'm sure there is some vignetting happening in all or
most cameras. I can notice near the extreme edges, the finder does not even
show a sharp image. However, I believe DOF preview should show a brightness
change at all apertures, on all lenses. The setup you're using with your
pentax lens though certainly might break a few rules here :)
Jim Davis
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