Historic B&L Lens Catalog from 1915.
https://archive.org/details/supplementno2too00bausrich
Historic B&L Lens Catalog from 1915.
https://archive.org/details/supplementno2too00bausrich
Very cool.... what is a periscope lens?
As I recall a spherical lens with the same (peri) curve on both surfaces.Originally Posted by mervinek
interesting. Thanks!
A while back someone was complaining that there were too many lenses on the market today.
The pricing is what really surprised me... not much of a difference from the manufacturing side! BTW this is a dream item of mine. I collect old books, so this would be the Holy Grail!
-kk
We were taught periscopic lenses were removed from flat base by having a +1.25 curve
Yes, look at old frames from the turn of the century and you will see why a flat lens were OK; small eye size reading glasses sitting on the end of the nose. We still apply the same basic principal with half eyes today. However as frames grew larger and we started to us glasses to correct myopia a flat ocular surface was impractical particularly as folks started to wear their distance vision glasses up on their noses as they do today.
Lens designers solved the problem of the lens being too close to the cornea by designing meniscus lenses first on a +1.25 base and later on a +6.25 base. That's why we still usually grind plano lenses on a +6.25 base.
Today, grind em for the frame. Optics be damned.
fantastic Dick, i was actually working with some of those lenses when i was with B@L in 1965, especially the crookes lenses, which the hippies just loved, crookes lens and octagonal wire frames
Ahh Crookes blue lenses - actually show how 'blue' light can be beneficial by reducing accomodative demand at near.
B
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