In article
>In article <32334331.6A057609@netjam.net> Brian
>
>> Sphere Cylinder Axis
>> -.50 -2.00 070
>>
>> So am i CORRECT in thinking I should just buy a -1 diopter, and thats
>> what I need?
>
>You might try it and se if it works -- but a -2.00 cylindrical correction
>means that you have lots of astigmatism. Without a custom-ground lens,
>you might be unable to correct enough.
>
>Here's a pragmatic way to tell. Can you read clearly without glasses?
>If so, at what distance? Suppose you can read clearly a book
>that is held 0.5m (about 19.5 inches) from your eyes. Then take
>the reciprocal of that distance (1/0.5 = 2.0), flip the sign, and
>that's the total diopter correction you need. In this particular
>example, a -1 diopter correction is just right, assuming that your
>camera finder already has a -1 correction.
>
>While we're at it, note that the built-in -1 correction means that
>the finder shows you a virtual image at a distance of 1 meter.
>
>Now, suppose that you have to hold the book closer in order to
>see it clearly. Say, 9 inches, or about 0.25 meter. Then you
>should be able to get by with a -3 lens on top of your -1 finder.
>
>If nothing works, you should consider having a custom-made correction
>lens for your eyepiece.
>--
> --Andrew Koenig
> ark@research.att.com
A good post, but, uh, what happens if he wants to take a vertical
photo, and the astigmatism correction is set up for a horizontal
camera position.....;-(
Hope This Helps