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Terry / Jim
Jim’s notes pushed me to contribute my 2 cents worth. I use Serengeti prescriptions lenses in a Bolle frame (not a graduated prescription). Lenses are polarized and quite dark L but a brown orange-tint which works excellently on clouds. I sometimes have difficulty seeing instrument faces (micro-air frequencies etc) but generally this is OK – the real benefit is outside. The bit about Jim’s comment that I wanted to pass on – my opto gave me the choice of a slightly-shorter or slightly-longer prescription than needed. I gather that our real requirements often fall somewhere between the stepped dioptre settings available in lense manufacture. In any event, I opted for the slightly-longer-than-necessary lenses, believing these to be better suited to discerning other planes at a distance. I am 100% impressed with them and would recommend others discuss exactly this with their opto at their next check. I think the combination of cloud-friendly-tint, polarization and slightly-longer-than-necessary prescription is a winner. Bit keen to try some of these yellow wrap-arounds for comparison too.
Cheers
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>>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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