Optical lenses have a front surface and a back surface. If you cut a cross section through the lens you'll see that both surfaces are curves (normally). For regular lenses or 'spheric' lenses, the curves are a single radius or circle. The curves for aspheric lenses are a 'compound curve' or not only a single radius but actually several radii combined to form the shape of the surface. Most aspheric lenses are only 'aspherically shaped' on one surface, usually the front for plus corrections for example, the back surface is either completely flat or very close to it. HD lenses are designed to be 'bi-aspheric' or to be compound curved surfaces on both the front and back, computer controlled to match your eye's specific correction - or at least that's the idea.
Of the few people I've heard from with HD lenses or bi-aspheric lenses, they've been very happy with the result (better be for $600) - but they had very complex prescriptions and were not happy with traditional lenses. If you're correction is not very complicated then you're not likely to benefit much from these advanced technologies. Check out this link for a graphic of Aspheric Lenses: http://www.qvision.ca/images/Diagram_AsphericLens.jpg Here is an example of Aspheric Lenses in a lab test: http://upload.wikimedia.org/wikipedia/en/4/49/OpticTest.gif Also some more technical information about the many types and shapes of Aspheric Lenses: http://www.kreischer.com/aspheric_design_guide.htm On May 16, 9:57 pm, Paul <[email protected]> wrote: > How different is this from aspheric lenses, which are also fairly > recent? Or is aspheric mainly for the purpose of making lenses > thinner, and doesn't improve the accuracy over the common spheric > lenses? I would guess that HD is a particularly fancy type of aspheric > lens. > > One thing to keep in mind. It's not as though your lenses stay in > exactly one place relative to your eyes. Adjusting the nosepieces (or > just moving the glasses with your hand) changes the position of the > lenses. > > Before plunking down a lot of money, it would be nice to hear from > some people who've tried them. --~--~---------~--~----~------------~-------~--~----~ Check us out at the oft-updated http://glassyeyes.blogspot.com! You received this message because you are subscribed to the Google Groups "GlassyEyes" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/glassyeyes?hl=en -~----------~----~----~----~------~----~------~--~---
