EOS Re: cross type AF sensors vs. aperture

[Henry Posner/B&H Photo-Video]

At 10:11 PM 2/2/2001 +0100, you wrote:
>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.

         I presume you meant <even at f/8>.

>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 alignment of the eye to the optical center of the finder at 
f/8 or slower to realize both halves of the split image is so precise that 
for ANY practical purpose it is rendered useless in the field.

regards,

Henry Posner/B&H Photo-Video
http://www.bhphotovideo.com
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