Monday, March 28, 2005, 6:14:00 PM, Jim wrote:
JH> Hi Godfrey:
JH> You're still a young man... I predict that you'll want a split image
JH> wedge on all of your cameras for manual focusing 20+- years from now
JH> when prespyopia catches up with you. :-)
How about a Messeraster screen than? Using similar principle as AF
sensors (and patented in the 50s). I just read about it somewhere
else, and it seemed interesting. Principle: it consists of many narrow
strips which are misplaced a tiny distance around the focal plane in
alternating fashion, and a thin hairline is perpendicular to them at
the places you want to focus on. The eye is excellent at comparing
slight changes of brightness of two spots next to each other, but
quite bad at evaluating microcontrast (that's how screens work). So
you just focus until the subject you focus on doesn't show a
difference in brightness in the Messraster anymore.
The promise was absolute accuracy because eye can compare even small
brightness differences very well.
>From what I saw, it was never made commercially, although just before
advent of AF Beattie supposedly considered making one.
Good light!
fra
