Let's Photograph Comet 46P Wirtanen

Paul Schlyter:
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?

20/20, or metric 6/6 = 1. It's explained at
https://en.wikipedia.org/wiki/Visual_acuity#Measurement. 20/25 for a
person like me with macular degeneration is considered to be very good.
Again, that's my left eye. I don't have a number for my right eye, but
subjectively, it is not very useful at the moment. We'll "see" what the
new eyeglasses bring in a couple of weeks.

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

On Mon, 24 Dec 2018 09:26:32 -0500, Davoud wrote:
20/20, or metric 6/6 = 1. It's explained at
https://en.wikipedia.org/wiki/Visual_acuity#Measurement.

Ok, so it measures the visual acuity at a distance of 20 feet. But
wouldn't a measure of (practically) infinite distance be more
interesting to skywatchers? No stars are only 20 feet away.

On Mon, 24 Dec 2018 22:33:39 +0100, Paul Schlyter
wrote:

On Mon, 24 Dec 2018 09:26:32 -0500, Davoud wrote:
20/20, or metric 6/6 = 1. It's explained at
https://en.wikipedia.org/wiki/Visual_acuity#Measurement.

Ok, so it measures the visual acuity at a distance of 20 feet. But
wouldn't a measure of (practically) infinite distance be more
interesting to skywatchers? No stars are only 20 feet away.

The distance is largely irrelevant. It's measuring resolution... the
ability to detect close high contrast features as separate from one
another. The distance of 20 feet is simply a standard so that the test
chart is always the same, and it's a distance that is practical in a
typical testing situation. Optically, 20 feet is pretty much the same
as infinity for the human eye in terms of accommodation.

Modern refraction techniques project patterns on the back of the eye
and directly assess accommodation, focus, and astigmatism. But this is
usually translated to the 20:X notation for simplicity.

On Sun, 23 Dec 2018 18:44:35 -0600, hleopold
wrote:

Fast moving indeed. As I mentioned earlier, few things move fast in the sky,
other than meteors which move very fast. But this was surprising to me even
knowing that it is fast. Thanks for that. How far from the Earth was it at
the time you took those shots?

At the imaging time of 17 Dec 2018 UT 10:00, the distance was 0.078
AU, 11.7 million km, 30.3 lunar distances. That was just about its
closest approach to Earth.

On Dec 23, 2018, palsing wrote
(in ):

On Sunday, December 23, 2018 at 4:38:10 PM UTC-8, hleopold wrote:

“I have an inferiority complex, but it's not a very good one.“ -
Vintagewheels

'When my kleptomania gets bad, I take something for it"
- Ken Dodd

Love it, and stolen. I have grabbed some good stuff from around the web for a
couple of decades, lost a bunch about a year and a half ago with the only
hard drive crash I have ever had, on a nearly 20 year old drive. I had 3
other drives on my computer, but I had the bad habit of not moving to a newer
drive for running my newsgroup reader AND my OS, so I lost 20 years of mail
as well. Now that really hurt.

--
Harry F. Leopold

The Prints of Darkness (remove gene to email)

“It would be a horrible embarrassment to be a a flesh-and-blood human and
still be unable to pass a Turing test.“-ErikF

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
aa #2076
AA/Vet #4
The Prints of Darkness (remove gene to email)

Greater love hath no man than this, that he lay down his self-respect for his
online enemies. - Teresita

On Dec 24, 2018, wrote
(in ):

On Monday, December 24, 2018 at 8:09:24 AM UTC-5, Paul Schlyter wrote:
On Sun, 23 Dec 2018 18:38:19 -0600, hleopold
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?

The '20' in the numerator means a 20 foot distance. If you can read the 20/20
line on the chart from 20 feet then your vision is average/normal.

If you can read the 20/15 line then your acuity is better than average;
others would have to be 15 feet away to read it.

If you can read the 20/100 line, and nothing smaller, then your acuity is
worse than average; the average person could read that line at 100 feet.

Thank you, that was much better than my description, shorter and made sense.

--
Harry F. Leopold
The Prints of Darkness (remove gene to email)

“He's so dumb he moves his lips when someone ELSE is reading.“-Doc
Smartass

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

On Mon, 24 Dec 2018 09:26:32 -0500, wrote:
20/20, or metric 6/6 = 1. It's explained at
https://en.wikipedia.org/wiki/Visual_acuity#Measurement.

Ok, so it measures the visual acuity at a distance of 20 feet. But
wouldn't a measure of (practically) infinite distance be more
interesting to skywatchers? No stars are only 20 feet away.

It is always nice to be able to actually FIND your telescope so you can look
at the sky. ;-0

--
Harry F. Leopold

The Prints of Darkness (remove gene to email)

“Damn. Someone's been ****ing in my genepool again.“-Kermit

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

On Sun, 23 Dec 2018 18:30:49 -0600,
wrote:
Way back in the late 70s early 80s I did, for a while, try photography with
my scopes, but otherwise I have been strictly a visual observer. I cant
believe the great stuff that we have these days. I am not really a fan of
digital photography in many ways, I loved shooting film, and that was how I
did astro photos back then.

You can still shoot film if that's what you enjoy to do.

The camera stores near me hardly carry any film anymore, except for 4x5 or
8x10. And I have gotten out of the habits I used to have. I love my smart
phone for its ability to grab shots that pop up unexpectedly. I also have a
very nice Leica digital camera (about 17 years old now. But I can never find
the charger for it half the time. My first camera was picked up in Hong Kong
when my ship stopped there in 1972. I picked up a fair amount of film, and
the battery died two days after we pulled out. This limited me to either .125
of a second, or Bulb. No light meter either. I picked up a couple of extra
batteries and a light-meter as soon as we hit Subic Bay a few weeks later.
That light meter was the second best buy I ever made.

What I really loved about my favorite film cameras was that they were grab
and shoot. I picked up in San Francisco’s Wolfes Cameras a couple of old
Leicas, one a red-dial 3F (I think) and a black-dial somewhat earlier model.
One was just the body, the other had the usual collapsable 50mm. I ended up
putting that lens on an old Canon B-2 I picked up as a much cheaper
alternative and found a couple of lovely Nicon screw-mount lens, one a 85mm
and one a 38mm. One was F 1.2 and I think the other was F 1.1 (Thank you for
holding those for me until I got back to shore, Ciddy). We are talking about
some big, heavy glass here. The 85mm was literally the size and shape of a US
hand grenade and just about as heavy. But it took beautiful photos. A big,
heavy, polished chrome hand grenade with a huge glass center.

I kept the Leica collapsable 50mm on the Canon B-2 as my “I am only
carrying one camera� "And no, I am not a camera geek� camera. “See, I
can practically put it in my pocket." Running around on a ship at sea you
don’t want to carry your favorite that might get damaged slamming into a
round-down or soaked in seawater. (Or strapped to the front of a bike or
motorcycle, which I did a lot riding through the hills of California.)

I find few cameras these days that do what I like to do, night-photography,
or as I used to call it, Available Darkness. This was nothing like those
wimps who did available light. ;-) That is where The Prints of Darkness in my
sig comes from, partly. I have been a printer for decades, mostly as a night
worker, I am a night person to begin with, I love astronomy. And I printed up
a lot of available darkness photos I took. Some even turned out pretty good.

Just about 18 years ago I found myself seriously thinking to buy a brand new
Voitlander (spelling?) A near copy of my old 3F. I had to step back and
really think about that and when I did I sadly passed on it. Lovely, but even
then I could see what was happening to film and I just could not justify it.
So a few years later I bought the digital Leica, if I had only waited a few
more years...

--
Harry F. Leopold

The Prints of Darkness (remove gene to email)

“(B)iological evolution is a team sport.“-Louis Friend

On Dec 24, 2018, Chris L Peterson wrote
(in ):

On Sun, 23 Dec 2018 18:44:35 -0600,
wrote:

Fast moving indeed. As I mentioned earlier, few things move fast in the sky,
other than meteors which move very fast. But this was surprising to me even
knowing that it is fast. Thanks for that. How far from the Earth was it at
the time you took those shots?

At the imaging time of 17 Dec 2018 UT 10:00, the distance was 0.078
AU, 11.7 million km, 30.3 lunar distances. That was just about its
closest approach to Earth.

That was about what I thought from what I had previously read. Yeah, that was
moving pretty good.

--
Harry F. Leopold

The Prints of Darkness (remove gene to email)

"We used to be afraid of comets. Now it's their turn." The Register