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Old December 25th 18, 05:04 AM posted to sci.astro.amateur
hleopold
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Default Let's Photograph Comet 46P Wirtanen

On Dec 24, 2018, Paul Schlyter wrote
(in t):

On Sun, 23 Dec 2018 18:38:19 -0600,
wrote:
On Dec 23, 2018, Paul Schlyter wrote
(in et):
On Sat, 22 Dec 2018 20:09:17 -0500, wrote:
My corrected vision in my left eye is 20/25, i.e., very good.


That's the same as 0.8 right? And full visual acuity would then be
25/25? Or 100/100 etc if you prefer that. Or just 1.0


20/20 is, as I understand it, perfect vision. Mine is 20/400 in

the
right eye uncorrected, corrected to 20/15. left is somewhat worse,

but
corrected to 20/15 also. Or it used to be, these days I am probably

more
20/20 or slightly worse. Plus they have to correct for the bad

astigmatism I
have in both eyes.


If the numerator is always 20, what does this 20 mean? Is 20/20 in
some way different from, say, 25/25 or.30/30?


As I understand it, you should be able to see at 20 feet as the average
person would see at 20 feet. (An average person with good eyesight of
course.)

If you are shown to have a 20/30 in your right eye it means that you see at
20 feet is like that “average” person would see at 30. In other words,
your eyesight is not that great.

My right eye, without glasses means that at 20 feet I see about as well as
the “average” person would see at 400 feet. In other words, pretty
poorly, than you add in the majorly bad astigmatism. Fortunately my eyesight
is pretty much correctable. to slightly better than average. I can, or could,
see as well at 20 feet as that “average” person can see at 15 feet.

Of course using glasses may correct your eyesight to “perfect” but there
are drawbacks, especially as you get older and need bifocals, which I have
used for about 12 years, my latest pair of glasses are line-less bifocals.
They are pretty good, but you have to actually use head movement to get the
right area to look through. Parallel lines are no longer so parallel and they
change as you move your head side to side or up and down. Plus things swell
up/shrink down as they move across the lens. (At least now I can actually see
the speedometer while driving, unlike when I used the old type of bifocals,
with those I had to move my head to actually read it, now I can keep my eyes
on the road as still read the speed.)

Oh yeah, and you can have either near-sightedness or far-sightedness. Mine at
age 12 was “perfect,” at age 12 and a half went near-sighted and kept
going that way. These days I am getting slightly better as my eyes age and
they attempt to become somewhat far-sighted, which in my case means that I
become very slightly less near-sighted.

And then of course there are lots of other problems you can have with your
eyes, one I have to keep track of is cataracts, I have them in both eyes, but
very mild so far and have been that way for at least a dozen years.

--
Harry F. Leopold
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AA/Vet #4
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