Definitive moon size illusion experiment

Tony Flanders wrote:

"Paul Lawler" wrote in message hlink.net...


One thing is to get your doctor to prescribe a pair of "astronomy glasses."
The difference between these and your regular prescription is that these are
focused at infinity (instead of some closer point as is done normally).


Actually, there's good reason to think that astronomy glasses should
be focused *beyond* infinity -- that is, they should be overcorrected
(for myopic people).

For only occasional astronomical use, yes. But for regular daytime use,
that's considered by most opticians that I've asked about, bad practice.

The myopic eye has a tendency to become "lazy". Give it reason to relax
its focusing system and it will stay there. In other words, overcorrect
myopia and then you will eventually need an actual correction for the
overcorrection.

I did this when I was 16. One of my pairs was overcorrected. Soon it was
insufficient, and I had to replace it. There is a good chance the
increase came as a result of my myopia not having been stabilized yet,
but nevertheless I remember having properly adjusted at some point to
the overcorrection and then feeling "blinder" when I took my glasses off.

The best strategy is to correct *exactly* for what you've got, which is
somewhat subjective, anyway, since the ophthalmologist relies on your
responses to determine what you see and what not and since myopia often
does not stabilize before the entire skull stops growing.

A good way to "cheat" a bit on the exam is to claim that you don't see
some of the smaller letters until the doc provides you with a lens that
will allow you to see slightly more clearly.

For those of us with astigmatism, things are even worse: I've spent one
hour with my o-doc trying to eliminate side ghosts from the image I was
viewing. The results are good for telescope and binocular usage and for
relatively dim objects, but I still see ghosts around the moon and
around bright nighttime objects when my pupils dilate.

It appears that astigmatism can be corrected only under the additional
assumption that the iris is not fully dilated. When it is, some
astigmatism persists, regardless of correction.

- Tony Flanders
--
I. N. Galidakis
http://users.forthnet.gr/ath/jgal/
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Eventually, _everything_ is understandable