Re: [ATM] Intentional astigmatism

["Scott Ewart" <scott.e@quicksurfer.com>]

Kevin,
    It doesn't really work to put a lens near the focal plane.  I asked 
Uncle Al about it once.  You need the correction after the eyepiece or close 
to the objective.  The simplest thing to do would be to have a lens with 
your prescription cut round to drop into the top of your low-power 
eyepiece(s).  You'd want to get one with anti-reflection coatings.  Of 
course, anyone else using your eyepiece would get the astigmatism, but it 
could be made to be easily removable, like under the rubber eye cup.
    It's the same as wearing the glasses, but a bit more comfortable.  I've 
thought of doing it myself, but my astigmatism isn't bad enough to need 
glasses, so I don't know my prescription.

Scott


----- Original Message ----- 
From: "Kevin Whitefire" <chaosopher23@yahoo.com>
To: <atm@atmlist.net>
Sent: Thursday, April 07, 2005 5:42 PM
Subject: [ATM] Intentional astigmatism


I'm wondering if it's possible to induce intentional
astigmatism in the focal plane, very weak astigmatism,
using a thin lens, that will compensate for my
eyesight.  Is this possible?

If it is, I see that it will have to be rotationally
variable and removable from the optical path for other
people and photography in order to work.

My astigmatism is rather minor, but annoying when I
look at either straight, parallel lines (sheet music)
or points of light (stars).  My eyeglasses have a
focal length of about 24 inches and vertical
astigmatism that gives a solar focus of about 3" tall.
 I'm far sighted with 20/25 and 20/30 without glasses.

Regards,
Kevin of Eastern Iowa
Seeker of the Darkness



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