The Extremely Large Telescope
Martin R. Howell
http://tinyurl.com/ya9p6va
Wouldn't it be great if this unit were equipped with optional visual
observation capability?
--
Martin R. Howell
The Astro Post
www.theastropost.com/smf
It's ALL there!
Davoud
> http://tinyurl.com/ya9p6va
>
> Wouldn't it be great if this unit were equipped with optional visual
> observation capability?
If by "great" you mean "great if it had visual capability and I, Martin
R. Howell had exclusive access," then I would say that for you, that
might be great.
If, however, one were to apply _my_ definition of "great telescope,"
which is, in part, "will enable many discoveries leading to new
understanding of the Cosmos and will be a worthwhile investment for the
taxpayers who paid for it," then I would say no, it would not be great
in any way for this telescope to have a standard ocular, even a very
good one.
Davoud
--
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
jerry warner
"Martin R. Howell" wrote:
> http://tinyurl.com/ya9p6va
>
> Wouldn't it be great if this unit were equipped with optional visual
> observation capability?
>
> --
But is your bed large enough for a Ford-950, and you!?
Chris L Peterson
<ilikestars...@universe.com> wrote:
>Wouldn't it be great if this unit were equipped with optional visual
>observation capability?
Seems like you'd see no advantage to this telescope unless you were
viewing at 6000X or more. And even so, everything would still look like
a gray smudge. There's a reason they don't bother with eyepieces on big
scopes.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
wsne...@hotmail.com
It would be better to wait for the IHT (Insanely Huge Telescope) to be
completed. I mean, if you are going to stand in line to get a look,
you might as well make it worth your while.
Pierre Vandevenne
<ilikestarsandyoudo...@universe.com> wrote:
> http://tinyurl.com/ya9p6va
>
> Wouldn't it be great if this unit were equipped with optional visual
> observation capability?
So outdated.
I'll want that to control the scope
http://www.computerworld.com/s/article/9141180/Intel_Chips_in_brains_will_control_computers_by_2020
and a high speed wireless link to feed data into this
http://news.bbc.co.uk/2/hi/science/nature/6368089.stm
That way, no need to pollute our way to remote cold places. And one
could still enjoy the comfort of some augmented reality porn while
observing.
Howard Lester
>>Wouldn't it be great if this unit were equipped with optional visual
>>observation capability?
> Seems like you'd see no advantage to this telescope unless you were
> viewing at 6000X or more. And even so, everything would still look like
> a gray smudge. There's a reason they don't bother with eyepieces on big
> scopes.
For the 6.5-meter MMT Observatory in Arizona we bought an AP 2" diagonal, a
TV 41mm Panoptic, and a JMI focuser to impress visiting "dignitaries." The
guys in the machine shop rigged up a way to mount the focuser, as of course
the telescope was not originally designed for direct viewing. I think that
setup yields 1427x. I never viewed through that, so I can't vouch for how
good it is, but I was never told of anyone's disappointment.
Chris L Peterson
<howardx...@verizon.net> wrote:
>For the 6.5-meter MMT Observatory in Arizona we bought an AP 2" diagonal, a
>TV 41mm Panoptic, and a JMI focuser to impress visiting "dignitaries." The
>guys in the machine shop rigged up a way to mount the focuser, as of course
>the telescope was not originally designed for direct viewing. I think that
>setup yields 1427x. I never viewed through that, so I can't vouch for how
>good it is, but I was never told of anyone's disappointment.
Yeah, I know of a couple of other cobbled setups like that at
professional observatories. I expect you could aim the scope at
anything, neglect to focus it, and maybe even leave the mirror cover
closed, and few would be disappointed after putting their eye to a
world-class research scope.
Bill Owen
> On Tue, 24 Nov 2009 19:04:30 -0800, "Martin R. Howell"
> <ilikestars...@universe.com> wrote:
>
>> Wouldn't it be great if this unit were equipped with optional visual
>> observation capability?
>
> Seems like you'd see no advantage to this telescope unless you were
> viewing at 6000X or more. And even so, everything would still look like
> a gray smudge. There's a reason they don't bother with eyepieces on big
> scopes.
... any more. Time was, the coude control room at the 200-inch (inside
the south pier) had an eyepiece you could move into the incoming light
path -- they'd use it as a preliminary finder, and then there was
another eyepiece which grabbed the light which did *not* go through the
spectrograph slit, and they'd use that for fine guiding.
I have vivid memories of looking at M57, Uranus, Neptune, and Jupiter in
spring 1974, while my advisor and the night assistant were busy inside
the coude room itself. Somewhere at home I still have a couple of punch
cards I made drawings on.
(Why those targets? They had just discovered the sodium cloud around
Io, and Guido Muench had time and wanted to confirm the observation. So
they put a multiple slit at the focal plane, to get coarse angular
resolution, and hoped to see a pair of Na D lines through each slit.
Now Jupiter was just coming back into the morning sky, so we had most of
the night to test the equipment, looking at extended sources with
emission lines -- planetary nebulae and anything else we could find. I
could easily see 4 of the 5 satellites of Uranus then known; Miranda was
too faint, and besides, we were looking through clouds. The first night
was mostly cloudy; the second night, Io was in transit; the third night,
we got good data and the confirmation Guido was looking for. I got to
guide an hourlong exposure, with Io on the slit and Jupiter in the FOV.)
-- Bill Owen
P.S. The movable eyepiece was from Edmund Scientific. I guess you
don't need the ultimate in quality when you've got an f/30 light cone.
dke...@hotmail.com
> On Wed, 25 Nov 2009 11:43:50 -0500, "Howard Lester"
>
Hi Chris
You should at least mention exit pupil and central obstruction.
I don't think some realize what these thing mean on a truly large
telescope.
Dwight
palsing
> Seems like you'd see no advantage to this telescope unless you were
> viewing at 6000X or more. And even so, everything would still look like
> a gray smudge. There's a reason they don't bother with eyepieces on big
> scopes.
Chris, I'll guess that you have never actually used a lot of glass
visually.
I can guarantee you that a lot of objects are considerably more than
just gray smudges when viewed through big aperture.
I was fortunate enough to spend 2 dusk-to-dawn new-moon nights viewing
through the 82" at McDonald Observatory in Texas, the lowest power
available being 812X at the F13.7 Cassegrain focus. Both seeing and
transparency those nights were close to 10/10
My observing report can be found here;
http://sites.google.com/a/pnalsing.com/www/82-report
Objects that are indeed gray smudges in my 25" have staggering amounts
of detail in the 82". It was hard to enjoy my own telescope for a
couple of months after that weekend ;>)
Next spring I have been invited to spend 5 nights using a friend's 48"
in west Texas, and I'm really looking forward to that, too.
When it comes to purely visual observing, there really is no
substitute for aperture, it just rules.
\Paul Alsing
Chris L Peterson
>Hi Chris
> You should at least mention exit pupil and central obstruction.
>I don't think some realize what these thing mean on a truly large
>telescope.
The exit pupil was implied in my calculation of 6000X (that's why this
is the minimum reasonable magnification). Obstructions might be an issue
in a few cases, but IMO obstructed optics don't have much impact on
visual use- especially on DSOs.
dke...@hotmail.com
> On Wed, 25 Nov 2009 10:20:03 -0800 (PST), "dkel...@hotmail.com"
>
> <dkel...@hotmail.com> wrote:
> >Hi Chris
> > You should at least mention exit pupil and central obstruction.
> >I don't think some realize what these thing mean on a truly large
> >telescope.
>
> The exit pupil was implied in my calculation of 6000X (that's why this
> is the minimum reasonable magnification). Obstructions might be an issue
> in a few cases, but IMO obstructed optics don't have much impact on
> visual use- especially on DSOs.
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatoryhttp://www.cloudbait.com
Hi
Just as the side of the exit pupil goes up with the size of the
primary, the
size of the obstruction goes up as well. When the obstructions image
at the pupil is large compared to the eye, it is pain to look through.
The effect
is that same on a smaller telescope with a longer focal length
eyepiece.
I would guess that most any magnification that was reasonable to use
would produce an image of the obstruction, at least as large if not
larger than the eye's pupil. To make such a large mirror useful,
one would have to go significantly off axis. I'd expect the coma to
be bad without some form of correction.
Even a 12 inch obstruction would be a pain at any practical
magnification.
Of course, a smaller secondary that didn't use the full amount of
light that
the primary was getting would be more practical.
Dwight
Chris L Peterson
> Even a 12 inch obstruction would be a pain at any practical
>magnification.
Well, my point was that practical magnifications for a scope like this
start at 6000X. And at 6000X, the shadow of the central obstruction will
not be a problem. Below 6000X, you're using less and less of the scope's
aperture, and naturally you'll reach the point where the CO and your
pupil are the same size- something most telescope users see only during
the day.
Paul Schlyter
@r24g2000prf.googlegroups.com>, pnal...@gmail.com says...
> On Nov 24, 9:08 pm, Chris L Peterson <c...@alumni.caltech.edu> wrote:
>
> > Seems like you'd see no advantage to this telescope unless you were
> > viewing at 6000X or more. And even so, everything would still look like
> > a gray smudge. There's a reason they don't bother with eyepieces on big
> > scopes.
>
> Chris, I'll guess that you have never actually used a lot of glass
> visually.
>
> I can guarantee you that a lot of objects are considerably more than
> just gray smudges when viewed through big aperture.
>
> I was fortunate enough to spend 2 dusk-to-dawn new-moon nights viewing
> through the 82" at McDonald Observatory in Texas, the lowest power
> available being 812X at the F13.7 Cassegrain focus. Both seeing and
> transparency those nights were close to 10/10
An 82" telescope is still of a reasonable size for visual use. The 42
meter scope will have an aperture of 1653", some 20 times larger than
the 82" scope you used, and will require a correspondingly higher
magnification if you want its exit pupil to fit within the pupil of
a human eye. If you don't use such a high magnification on that
monster scope, you're wasting its big aperture and might as well
have used a smaller scope.
jerry warner
Howard Lester wrote:
... which brings up a very LARGE point! The public
are either morons or their expectations are very low, or
they trully dont know the difference, or you could show
them Monroes belly button at 1700x and they would still
smile (and observatory directors smile also come funding
time!), or ..................................................................
Because I know a club that hasnt had a working telescope
(even a modest sized one) since its founding years ago,
and they literally dont give a crap - they rely on free scopes
and large fundings which they divert to other black holes.
There must be something in this I trully dont understand.
Over the years not one soul that I know about ever complained.
Good telescope operators were run out of the club in
favour of idiots, and the scam goes on. (from my point
of view).
From this simple fact alone the whole composition and
mission of the club has changed. Total arrogant idiots
who know absolutely nothing about astronomy or telescopes now run everything,
and launch their orders
like missles at the few remaining 'club' members who
must show up to help scouts and their parents see blurry
images, week after week after weary week.
The people who know the difference stay silent.
I guess its a commercial venture now, this club,
and telescopes and astronomy and science are a mute
point and even the guy who runs the B&C now brags
about ............... 5000x power!
Three members finally volunteered to buy this club a
CGE-14 and they turned that down!
What in hell explains this syndrome?
wsne...@hotmail.com
> In article <1593732c-1123-43e3-9791-9dd0121b0818
At 6000x, even a 100-degree AFOV eyepiece is only going to have a
field-of-view of 1 arc-minute. Most of the well-known objects are
much larger than that, so you would have to concentrate on the more
interesting features of those objects, (globs in neighboring galaxies,
for example.) However millions of smaller, fainter targets would be
accessible.
Bhogi
<ilikestarsandyoudo...@universe.com> wrote:
> http://tinyurl.com/ya9p6va
>
> Wouldn't it be great if this unit were equipped with optional visual
> observation capability?
>
> --
> Martin R. Howell
> It's ALL there!
Just for the sake of argument, if we mounted a giant wide apparent
field of view "eyepiece" with exit pupil of say 0.5m, wouldn't that be
like looking at 100x magnified stars and galaxies thru a window? A
massive overkill, I know, but it would be really impressive.
dke...@hotmail.com
Hi
Exit pupil is not a factor of only the eyepiece, it is primarily a
factor of
the focal length of the primary, the eye pieces focal length and the
limiting
element of the system ( secondary or primary diameter ).
The eyepiece can control the distance to the eye, by design, and can
change the
distance to the exit pupil but this has little effect on the diameter
of the exit pupil
for a given eyepieces focal length.
You need to understand what exit pupil is before you can understand
why
a wide angle eyepiece does not change it. Exit pupil is the image of
the primary
( or limiting obstruction as mentioned earlier with the secondary )
that is
projected by the eyepiece.
A wide angle eyepiece has a light path though it that takes a larger
amount
of physical area at the field stop through the internal lenses to the
eye
at wider angles. This alone has no effect on exit pupil size.
Eyepieces that extend the distance that the exit pupil is from the
eyepiece
actually decrease the exit pupil size slightly but the effect is small
because
of the large distance of the primary compared to the placement of the
negative lens compared to the positive lenses in the eyepiece.
Dwight
Bhogi
Ok, forget wide angle than.
My idea was simply that exit pupil is so large you can move your head
around and still see everything because the head is still in the exit
pupil - like looking thru a window at a highly magnified night sky.
That's why I also said 100x magnification instead of 6000x like
proposed before.
If one was making such an insanely large and expensive "headpiece" one
would surely match it to the extremely large telescope. Think of how a
fly could observe thru normal eyepiece.
Does that make sense?
Ken S. Tucker
What we've done (it's rather common), is to fit a TV camera
to the focus, then you can go to a wide screen TV.
Get's ya the same effect.
Ken