Actually, the problem is quite different than the problems of camera
lens design, but the demands are certainly significant, as they only get
to use one element. As the eye swivels, it not only looks through the
lens at a different angle, the iris moves. Most eyeglasses just use
spherical sections and ignore this problem both because of the reason
you gave and for cost and speed of delivery. There are aspherical
designs to compensate, but they are more expensive and take a week or
more to ocme from Japan. Also, if you are wearing progressives, only the
top section and a vertical section down the center are corrected for
your vision. There are large areas of the lens that are defined as not
focusing properly, adding to the 'tunnel' feeling. More expensive
designs have wider in-focus areas.
Moose
Jeff Keller wrote:
I don't know about other eyeglass users but my angle of sharp vision is
a very narrow tunnel. Since my eyes automatically point at what I'm
interested in, everything "appears" sharp. I don't think the demands on
eyeglasses are anywhere near as tough as for a photographic lens. When I
look out through the extreme edges of my eyeglasses the image isn't as
sharp but I suspect that is due more to a curved image plane and old
eyes that don't focus very far rather than the effects of dispersion.
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