>>graduated ones with
polarizing magnetic clip-ons <<
Interesting notes Terry. I have
tried a similar setup but one of our club members warned us of a
significant danger in graduated lenses for gliding . .
In his considered opinion we should
have a driving/gliding prescription made to give 'exact focus at
infinity with the eyes at rest' to see those vital threatening specs
during lookout, not to mention dust and birds that mark the thermals! A graduated lens apparently does not do this
well as you cannot rely on your eyes always being focussed at infinity.
Now, having the 'focus at infinity
with the eyes at rest' means that our short vision is poorer than
normal - being exacerbated by the main lens being set longer than
for normal civilian use. This means that a (narrow) bi-focal region is
usually needed - focussed to see maps and instruments at arms length
(perhaps 300 to 800mm?).
Perhaps I can try to explain
further. If the opto does his normal job he will choose a lens that
works fine at (guessing the numbers here) 20m and infinity, but is
actually best at 200m and 'pretty good' at 20m and infinity. David
suggests that the sweet spot should be at infinity, not 200m. Thus the
lens might work 'pretty well' from say 50m to beyond (!) infinity but
is actually perfect at infinity, thus making a greater need for
bi-focal or even trifocals. My first set made like this have been great
although the bifocal part is too wide and next time I'll get it made to
'28' not '35'. Looking forward to the benefits of polarizing too.
I've also been contacted offline by
a fellow pilot been using such a setup for years - no worries.
>>It would be interesting to know if it's possible to get
"clear", that is non-tinted polarizing glasses (or clip-ons) as used in
photographic polarizing filters<<
What a great idea Terry!
This has been a most interesting
thread, I hope that we all get to benefit in the air! Thanks to all for
your valuable contributions.
Cheers,
Jim Kelly
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