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Message: <blockquote data-quote="typo" data-source="post: 3537157" data-attributes="member: 83808">I mentioned earlier on that I normally wear glasses when using binoculars. I've checked a few time overmthe years and I definitely see more detail in bright conditions with glasses, but Pinwoods comment in #11 got me thinking a little. Does the affect of astigmatism change with light level as he speculates?Previously I've done this kind of comparison in bright conditions, often with the binocular on a tripod to get something pretty accurate, but this was a bit rough and ready. The light levels were controlled by curtains. Tthe comparison was done hand held, but sitting with an USAF chart at 20 ft. There was a consistent two pattern or 25% advantage with glasses. That works out as 20/15 at the brightest levels down to 20/30 in the darkest conditions with glasses  and 20/19 down to 20/28 without. This was a just a one eye comparison. I don't have my prescription but I remember my right eye was 1.0d and 90° cylinder which might help for comparisons.I don't know why the level of astigmatism couldn't change as the pupil dilates, but it doesn't seem to make any demonstrable difference over something like a 1000 fold range in light levels for me.David</blockquote>