On 13 Nov 2002 11:25:26 -0800, rcochran@lanset.com (Richard Cochran) wrote:

>Note also that if you're astigmatic, the correction eyepiece must
>be aligned to your EYE, not to the camera's viewfinder. In other
>words, when switching from horizontal to vertical, you must rotate the
>eyepiece in its frame by 90 degrees (or rotate your head to keep your
>eye aligned with the corrective eyepiece). To get an idea of the
>problem with your own eyes, remove your glasses and try looking through
>the lenses when they're rotated 90 degrees. With my own -3.25 cyl
>astigmatism, the view is quite a bit worse with a misaligned correction
>eyepiece than with no correction at all. If you're fortunate enough
>to have no astigmatism, you'll be able to see clearly through your
>eyeglasses (or a camera's corrective eyepiece) no matter how you
>rotate the lenses.

If you have astigmatism and a problem with age-related
inability to focus your eye, there are two solutions:
1) Use normal glasses and add needed correction for
seeing the viewfinder screen sharply with eyepiece
correction.
2) Use a variation on normal bifocal glasses that
permits correct screen focus with the dominant eye
(described at: www.David-Ruether-Photography.com/articles.html#glasses).
This solution has the advantage of providing better
vision all of the time, not just for photography...