I don't have a good source from a pure optical point of view, but various
attempts have been made in Olympus lens catalogues etc. Basically
astigmatism is when the focal length of an objective (like your eye - lens)
is different for different angles around the axis. Therefore something is in
focus maybe vertically, but out of focus horizontally, for instance. The
correction is a cylindrical lens aligned precisely along the line of the
astigmatism, which can only be achieved by contact lenses (although how they
stop these rotating is a mystery to me) or glasses, as objects which don't
have a fixed angular relationship to your eye will not deliver the alignment
required, although as Chris says, if the astigmatism is mild, the correction
could be better than nothing. The problem is that if you rotate the
correcting lens through 90 deg in either direction, it becomes the precise
opposite of what you need.
Julian
Cambs, UK
----- Original Message -----
From: <bsandyman@xxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Tuesday, January 21, 2003 9:34 PM
Subject: Re: [OM] Eyecup question
> I suppose you could get two eyecups. One corrected for vertical, and the
other
> for horizontal. (Of course what would you do for those rare artistic
diagonal
> shots?:-)
>
> I take it from your comments that astigmatism corrections only work in one
> direction. Is there somewhere I can read an explanation of this. I am
curious.
> Thanks!
>
> Date: Tue, 21 Jan 2003 14:03:00 +0000 (GMT)
> From: julian_davies@xxxxxxxxxxxxxx
> Subject: Re: [OM] Eyecup question
>
> You can't do astigmatism with one of these - you turn the camera portrait
and
> landscape! I wish this were possible as I have the same affliction. It
would be
> very hard to align the circular lens when mounting it in an eyecup1. the
square
> for 2 would be easier, but then the original problem applies.
>
> Julian
>
> --
> Clendon
>
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