On Fri, 2 Feb 2001, Bob Meyer wrote:
> Anyone who's old enough to remember manual focus SLRs
> with a split-image "rangefinder" in the viewfinder is
> probably familiar with what happens when you mount
> slow lenses on the camers (or view with the lens
> stopped down). For those without that experience,
> I'll tell you: one half of the split-image blacks
> out. ...
Hi Bob,
I also used to think the split-image blackout was due to
the lens aperture limit.
Then I put a split image focussing screen in my EOS 1000FN
and discovered that blackout is entirely due to positioning
of the eye relative to the centre of the split prism!
If one side blacks out (even at f/1.8), I just move my eye
relative to the viewfinder until both halves of split images
become visible again. The effect is still there, but less
subtle when using the triangular "microprism" collar.
The split images are still visible even if I mount a lens
with effective aperture f/11 (f/5.6 + 2x TC). It *is*
harder to focus, no because of "blackout", but because the
two split images have a greater DOF.
The situation is similar to using FTM during DOF preview.
Cheers
Julian Loke
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