On Mon, 18 Mar 2013 12:42:17 -0400, Art Todesco
wrote:

On 3/18/2013 11:13 AM, bud-- wrote:
On 3/18/2013 4:35 AM, Jim Elbrecht wrote:
I know what size I need-- and I can try these on to see if they work
for me--

But I have 100 or so glasses of varying magnifications and I want to
sort and label them.

Is there an easy/cheap method of measuring magnification?

Web searches are just turning up pages telling me how to figure out
what strength I need. I want to know what strength I *have*.

Thanks
Jim

You can find the focal length by focusing the sun (parallel rays) on a
target and measuring the distance from lens to target. (To state the
obvious, the target and lens have to be at right angles to the sun 'rays'.)

According to
http://en.wikipedia.org/wiki/Diopter
"A ... diopter, is a unit of measurement of the optical power of a lens
or curved mirror, which is equal to the reciprocal of the focal length
measured in metres (that is, 1/metres)."


[An ophthalmologist I go to said lenses with the same diopter may not be
the same, which does not make sense to me. He also said he could not
give me a strength for reading glasses from the prescription he wrote,
even though the prescription seems to be in diopters.]
1st of all, he may have been referring to other specs on lenses like
astigmatism, which is the difference between horizontal and vertical
magnification.

Astigmatism is a little more complicated than that. There is an angle
thrown in there, too. Basically it's the difference between a
spherical lens and a cylindrical lens, with "strength" and angle of
the cylinder.

Plus there are others, which are way beyond my
understanding. But, if he won't give you the information, find a new
eye doctor.

+1

BTW, someone once told me to never go to an ophthalmologist
for fitting glasses .... optometrists do a better job because this is
what they do. And, not all optometrists are created equal.

Not all ophthalmologists are created equally, either. ;-) However,
if you don't have any abnormalities, going to an MD is a waste of his
time and your money. You're better off with a good OD (how to find
one is another issue). An OD can easily refer you to an
ophthalmologist, if necessary.

As for
'readers' it's not that big a deal, unless you have a more complicated
prescription.

Prescription "readers"? I thought the definitions were opposite
(prescription, off-the-shelf). I do have prescription glasses for
reading but I've never heard them referred to as "readers".

Use what works for you for the task you are doing.
Actually, my wife has a very difficult prescription for contacts,

Some can't be fitted for contacts at all.

however, any readers work for her ... she uses mine.

Strange. She must just be near sighted. I wouldn't think that would
be a problem for contacts at all.