optical illusion or atmospheric effect?

Tonight, I was looking up at the sky around midnight. I noticed that
almost all of the stars looked doubled. The brighter the star, the more
noticeable the effect. Just looking at them naked eye, not through
telescopes or binoculars or anything. The funny thing was that when I
looked at them true naked eye (i.e. without my glasses), the doubling
appeared horizontal, but when looking at them through my glasses, the
doubling appeared vertical. Is there a known atmospheric effect that can
do this? I would estimate the separation between the doubled stars was
about 2-5 arcseconds, either horizontally or vertically.

Yousuf Khan

On 5/24/12 11:34 PM, Yousuf Khan wrote:
Tonight, I was looking up at the sky around midnight. I noticed that
almost all of the stars looked doubled. The brighter the star, the more
noticeable the effect. Just looking at them naked eye, not through
telescopes or binoculars or anything. The funny thing was that when I
looked at them true naked eye (i.e. without my glasses), the doubling
appeared horizontal, but when looking at them through my glasses, the
doubling appeared vertical. Is there a known atmospheric effect that can
do this? I would estimate the separation between the doubled stars was
about 2-5 arcseconds, either horizontally or vertically.

Yousuf Khan

This effect is in your eyes--aberrations are exaggerated at larger
apertures expected in the dark. I'm assuming you have corrections
for astigmatism in you glasses prescription.

On 25/05/2012 12:47 AM, Sam Wormley wrote:
On 5/24/12 11:34 PM, Yousuf Khan wrote:
Tonight, I was looking up at the sky around midnight. I noticed that
almost all of the stars looked doubled. The brighter the star, the more
noticeable the effect. Just looking at them naked eye, not through
telescopes or binoculars or anything. The funny thing was that when I
looked at them true naked eye (i.e. without my glasses), the doubling
appeared horizontal, but when looking at them through my glasses, the
doubling appeared vertical. Is there a known atmospheric effect that can
do this? I would estimate the separation between the doubled stars was
about 2-5 arcseconds, either horizontally or vertically.

Yousuf Khan

This effect is in your eyes--aberrations are exaggerated at larger
apertures expected in the dark. I'm assuming you have corrections
for astigmatism in you glasses prescription.

Well that's possible, and I do have astigmatism, but today was the only
day I've ever seen this.

Yousuf Khan

On 25/05/2012 05:34, Yousuf Khan wrote:
Tonight, I was looking up at the sky around midnight. I noticed that
almost all of the stars looked doubled. The brighter the star, the more
noticeable the effect. Just looking at them naked eye, not through
telescopes or binoculars or anything. The funny thing was that when I
looked at them true naked eye (i.e. without my glasses), the doubling
appeared horizontal, but when looking at them through my glasses, the
doubling appeared vertical. Is there a known atmospheric effect that can
do this? I would estimate the separation between the doubled stars was
about 2-5 arcseconds, either horizontally or vertically.

I suspect if you look at your glasses prescription you will find it has
a fair amount of correction for cylindrical astigmatism. The formula
only works correctly at the right distance and light levels.

When your eye is dark adapted and the pupil wide open abberations are
much worse than normal (also why they do eye tests in a darkened room).

With your glasses on your long distance vision is over corrected at
infinity and without them it is under corrected. The result is you see
each star as two spots or a line : or ..

ITYM 3-5 arc minutes separation too.

--
Regards,
Martin Brown

Yousuf Khan wrote:
Tonight, I was looking up at the sky around midnight. I noticed that
almost all of the stars looked doubled. The brighter the star, the
more noticeable the effect. Just looking at them naked eye, not
through telescopes or binoculars or anything. The funny thing was
that when I looked at them true naked eye (i.e. without my glasses),
the doubling appeared horizontal, but when looking at them through my
glasses, the doubling appeared vertical. Is there a known atmospheric
effect that can do this? I would estimate the separation between the
doubled stars was about 2-5 arcseconds, either horizontally or
vertically.
Yousuf Khan

I'll agree with the other responses that this is astigmatism in your eye,
and add that spectacle corrections are not always perfect, which is why you
still saw some residual astigmatism in the perpendicular direction. I once
got prescription lenses that actually made vision in one eye worse, and was
told that, "Well, the angle tolerance allowed in the workshop is 20 degrees
+/-, good enough for most people." I told the optician to send it back and
get a new one made, which was spot on, and gave complete correction, at
their expense.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

Mike Dworetsky wrote:
Yousuf Khan wrote:
Tonight, I was looking up at the sky around midnight. I noticed that
almost all of the stars looked doubled. The brighter the star, the
more noticeable the effect. Just looking at them naked eye, not
through telescopes or binoculars or anything. The funny thing was
that when I looked at them true naked eye (i.e. without my glasses),
the doubling appeared horizontal, but when looking at them through my
glasses, the doubling appeared vertical. Is there a known atmospheric
effect that can do this? I would estimate the separation between the
doubled stars was about 2-5 arcseconds, either horizontally or
vertically.
Yousuf Khan

I'll agree with the other responses that this is astigmatism in your
eye, and add that spectacle corrections are not always perfect, which
is why you still saw some residual astigmatism in the perpendicular
direction. I once got prescription lenses that actually made vision
in one eye worse, and was told that, "Well, the angle tolerance
allowed in the workshop is 20 degrees +/-, good enough for most
people." I told the optician to send it back and get a new one made,
which was spot on, and gave complete correction, at their expense.

I'll just add, I took off the faulty spectacles and held them up while I
rotated them, and at one point with about 25-30 degrees tilt, the vision
correction was excellent, which is how I knew the angle ground into the lens
was off.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

On 5/25/2012 3:49 AM, Mike Dworetsky wrote:

I'll agree with the other responses that this is astigmatism in your
eye, and add that spectacle corrections are not always perfect, which is
why you still saw some residual astigmatism in the perpendicular
direction. I once got prescription lenses that actually made vision in
one eye worse, and was told that, "Well, the angle tolerance allowed in
the workshop is 20 degrees +/-, good enough for most people." I told the
optician to send it back and get a new one made, which was spot on, and
gave complete correction, at their expense.

That optical shop was lying to you. The angle tolerance in cylinder is
supposed to be only TWO degrees, not twenty, depending on the amount of
cylinder in the prescription.

Bud

On 25/05/2012 3:06 AM, Martin Brown wrote:
I suspect if you look at your glasses prescription you will find it has
a fair amount of correction for cylindrical astigmatism. The formula
only works correctly at the right distance and light levels.

When your eye is dark adapted and the pupil wide open abberations are
much worse than normal (also why they do eye tests in a darkened room).

Which would make some sense, as we just got back from watching a movie
(in a darkened theatre, obviously). On other nights, I don't have any
problems, since I'm coming out from lighter environments.

With your glasses on your long distance vision is over corrected at
infinity and without them it is under corrected. The result is you see
each star as two spots or a line : or ..

ITYM 3-5 arc minutes separation too.

Interesting, describes almost exactly what I saw.

I wonder if it's worth getting a new prescription done, based on this
situation? Or will getting a prescription corrected on watching stars
make the glasses useless for regular use?

Yousuf Khan

William Hamblen wrote:
On 5/25/2012 3:49 AM, Mike Dworetsky wrote:

I'll agree with the other responses that this is astigmatism in your
eye, and add that spectacle corrections are not always perfect,
which is why you still saw some residual astigmatism in the
perpendicular direction. I once got prescription lenses that
actually made vision in one eye worse, and was told that, "Well, the
angle tolerance allowed in the workshop is 20 degrees +/-, good
enough for most people." I told the optician to send it back and get
a new one made, which was spot on, and gave complete correction, at
their expense.

That optical shop was lying to you. The angle tolerance in cylinder
is supposed to be only TWO degrees, not twenty, depending on the
amount of cylinder in the prescription.

Thanks. It was the optician's assistant who said this to me, not the lens
maker, who is located a long way from London.

Well, you may be right. Though judging 2 degrees from looking at letters
and spots, and listening to the patient saying, "Maybe this one is a bit
better than the last one," and adjusting the angles on test lenses during
an exam, seems to be expecting a lot from the optician. OTOH if you say the
tolerance allowed for the lens maker is 2 degrees variation from the
prescription, this makes more sense.

I'll check it out. Since changing opticians a decade ago (after moving to a
new address) I haven't had any further problems with these prescriptions.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

On 5/25/2012 10:34 AM, Mike Dworetsky wrote:
William Hamblen wrote:
On 5/25/2012 3:49 AM, Mike Dworetsky wrote:

I'll agree with the other responses that this is astigmatism in your
eye, and add that spectacle corrections are not always perfect,
which is why you still saw some residual astigmatism in the
perpendicular direction. I once got prescription lenses that
actually made vision in one eye worse, and was told that, "Well, the
angle tolerance allowed in the workshop is 20 degrees +/-, good
enough for most people." I told the optician to send it back and get
a new one made, which was spot on, and gave complete correction, at
their expense.

That optical shop was lying to you. The angle tolerance in cylinder
is supposed to be only TWO degrees, not twenty, depending on the
amount of cylinder in the prescription.

Thanks. It was the optician's assistant who said this to me, not the
lens maker, who is located a long way from London.

Well, you may be right. Though judging 2 degrees from looking at letters
and spots, and listening to the patient saying, "Maybe this one is a bit
better than the last one," and adjusting the angles on test lenses
during an exam, seems to be expecting a lot from the optician. OTOH if
you say the tolerance allowed for the lens maker is 2 degrees variation
from the prescription, this makes more sense.

I'll check it out. Since changing opticians a decade ago (after moving
to a new address) I haven't had any further problems with these
prescriptions.


The tolerance, of course, is in the lens fabrication, which is why the
statement about plus or minus twenty degrees _in the workshop_ was bunk.
Clinical error is another thing altogether, but a careful eye doctor
and a willing patient should be able to get the angle closer than plus
or minus 20 degrees. Your correction isn't ever 100% stable, either.
You need to get it checked periodically. I myself have irregular
astigmatism in my right eye that makes it impossible to reach an
end-point correction in the eye doctor's chair. We go until we get
tired of trying. Roughly 20/25 (6/7.5) is about the best acuity I've
ever had in that eye. The left eye, although it takes a stronger
prescription in both sphere and cylinder, will be 20/20 (6/6) with the
right prescription.

Bud