In article
<acb831b3-8e3b-402a-afa8-554a6710699e[at]l13g2000vba.googlegroups.com> ,
AndyHancock <AndyMHancock[at]gmail.com> wrote:

- quote -

I think that the frame discussion is a red herring. Seldom will you use
the lenses near the edge. The figure of merit for optimization should
not weigh performance looking through the lens near the periphery very
heavily. The fitting of the lens into a frame will be the least of your
problems. The opticians should have templates for edging the lenses to
fit almost any frame. The should even be able to make a template from
frames in hand.

One of the tradeoffs to be used in the optimization should be the
effects of centering error on performance.

You should realize that various practitioners have their own biases.
They may not even know them. While there are some out and out charlatans
out there, you should worry at least as much about true believers.
Remember that surgeons will lean toward cutting while pharmacologists
would prefer all manner of drugs. Each could honestly think that their
approach is best for the patient.

In short, I think you have unrealistic expectation for the benefit to be
gained by using aspheric lenses. I cannot imagine that you will not be
disappointed.

I am not a health professional. What little experience I have with
aspheric design leaves me highly skeptical. What I believe, without
proof, is that a small pupil size in bright light enables people to
tolerate aspherics much better than the would in dim light. Moreover,
the lens can be designed for best performance on-axis. There is where
the benefit lies.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

On Mar 29, 2:59*pm, Salmon Egg <Salmon...[at]sbcglobal.net> wrote:
- quote -

I'm not completely unfamiliar with the world of optics (in dielectric
waveguides rather than geometric optics) and of optimization, so I get
the gist of your description. It would still be nice to know whether
not maintaining the same frames would mess up the comparison between
aspheric and spheric.

On a separate vein, I noted some experts vigorously defend the merit
of aspherics, attributing the problems to fitting and dispensing. For
me, it does not matter what the source of difficulties are. If the
state of practice for dispensing and fitting is not mature enough to
be uniform and reliable for aspherics, that has the same effect as
unreliable aspheric technology in the design/manufacturing realm --
maybe even worse, since it costs much time and good will in repeated
attempts at refitting, and maybe even redispensing.

On Mar 29, 2:25*pm, "Mike Tyner" <mty...[at]mindspring.com> wrote:
- quote -

I would like to avoid the variation that comes from putting lenses
into the frame before each trial.

But more importantly, I want to be able to instantly switch, as often
as necessary, so that I can clearly notice the difference. Otherwise,
I would not have confidence in the comparison.

In article
<a7411cbd-2c2e-43a0-b638-a6e483ec5908[at]e10g2000vbe.googlegroups.com> ,
AndyHancock <AndyMHancock[at]gmail.com> wrote:

- quote -

You probably have run into the unpleasant truth about aspherics. The are
not a panacea. St best, they will be a compromise among conflicting
demands.

As far as I am concerned, an aspheric lens will be best when it is used
to form am image of a known point, to a known point under unvarying
conditions.

Th usual design process will usually use a computer. The design will
depend upon maximizing a figure of merit. To get the figure of merit for
a given lens, many points are imaged onto the computer retina from many
locations. A weighted average is taken for the performance for this set
of point for the various conditions. That gives you the figure of merit.

How to weight this average, is open to argument. You probably do not
even know what properties would be most valuable or least desirable for
yourself. I certainly would expect that a design that improves one
aspect will degrade another.

Good luck. Keep on searching for the holy grail.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

"AndyHancock" <AndyMHancock[at]gmail.com> wrote

- quote -

It shouldn't be hard to make a pair of spheric lenses to fit your
discontinued frame. Tell them you want to keep your old lenses and you could
swap them out once or twice to examine the difference.

-MT

I owned glasses for about 10-15 years before replacing them. They
were aspheric lenses from a reputable glasses shop, and image was
blurry when I gaze about 30-40 degrees away from centre i.e. my
eyeball is rotated so that pupil is staring through a point on outer
side (left/right) of the lens. High index plastic with AR and scratch
resistant coatings. I am not concerned about bending of straight
lines, or prism effect where edges seem to bleed different colors.
The simple blurriness was the main thing I was trying to solve. After
many adjustments (about 1.5-2 hours each, including travel), I simply
went back to my old, old glasses. I did the reading about the
different aberrations, the various fitting

Now , more than half a decade later, I tried again with another
reputable glasses shop. Same problem, despite follow-up checks on
adjustment. Rather than bothering the people (and myself) with
repeatedly with futile adjustments, I decided to buy a second pair of
glasses, everything the same except with spherical lenses.
Unfortunately, the frame was no longer available (this is about a
month after receiving my first new glasses). So I can't do an
experiment where all factors (including the frame and the glass shop)
are the same except whether the lens is spherical or aspherical.

Rather than compromise the experiment, I decided to read up (again).
According to http://en.wikipedia.org/wiki/Aspheric_lens, aspherics
improve cosmetics, but not vision.

In contrast, http://www.allaboutvision.com/lenses...ric-lenses.htm
says that aspherics reduce distortion when gazing off-centre, though
it doesn't say whether they are referring to blurriness (see section
"Superior Optics of Aspheric Lenses" -- the reference to clear imaging
seems to refer to blurriness, or lack thereof). This is the *only*
site I've found that indicates an improvement in vision. All other
explanation of asphericity shows columnated light approaching a lens
along its longitudinal axis, and showing a single point focal point
instead of the smeared focal point of spherical lenses.

I have two questions in the following paragraphs that I'm hoping the
experts here could respond to.

I asked at another optical outlet about aspherics...whether it is
meant to optimize parts of an image that is well off-centre when the
user is gazing out the optical centre, or whether it optimizes the
central part of the image when a user's eyeball is rotate away from
the optical centre. Apparently the latter, and the above site on
"Superior Optics of Aspheric Lenses" corroborates. Is this true?

Since I can no longer obtain the frames that I have (verified by
contacting suppliers through-out North America), and I'm not a web-
buyer, would there be any merit to any experiment where the frames for
the aspherics differ from my current frames for the aspherics?

Thank you.