Tweets, thanks for the education re contact lenses and bins; I was out
of town for most of the past week (and finally saw a Limpkin), hence
this belated reponse.

Because my eyes are not all that bad (-0.75, -1 diopter, no astigmatism),
I get a fine view using just my eyes with bins -- and I can still locate
birds without glasses, they just aren't as sharp as they are with glasses.
My bins do have decent eye relief (Leica 10x42), and I can see the whole
view using them with glasses, but the quality of the view just isn't as
good as it is without them (seems kind of "veiled"). My concern is that
contacts might also alter (at least slightly) the image. And I have
noticed that several experienced birders use glasses, not contacts, in
the field (responses here suggest that this is probably because glasses
can do a better job of correcting for astigmatism). My opthalmologist
could not answer my question about contacts and bins, by the way: she
suggested asking other birders about it...

Some other tweets indicated an interest in this question, so I'll
summarize some of the direct e-mail: A couple of people indicated
that contacts do not degrade the binocular image at all (compared to
simply allowing the bins to correct for near-sightedness). Another
near-sighted birder says she is happy with a version of "monovision"
-- using a contact lens on one eye for distance vision, and nothing on
the other eye for close vision (sounds great, though I have read that
monovision can affect depth perception, etc.).

David Wright
Seattle, WA
dwright at u.washington.edu