Why can't I resolve deep sky objects?
Bob Feduniak
problem, but I don't think a major one. I've been trying with no
success to get a clear view of M13, using eyepieces ranging from 40mm
down to 10.4mm. At the lower magnifications, it looks like a
moderately bright star; at higher magnifications, it looks like an out-
of-focus blob that seems very roughly to have the shape of M13 (based
on photos). I cannot resolve even two stars, much less the dozens
that I think should be distinguishable. I'd appreciate any thoughts
or suggestions.
Bob Feduniak
lal_truckee
> I'd appreciate any thoughts
> or suggestions.
Collimate.
David Nakamoto
collimate that scope. The latter you can get the instructions through a
Google search. Try the search strings "collimate" and "SCT".
--- Dave
Per Erik Jorde
> I cannot resolve even two stars, much less the dozens
> that I think should be distinguishable. I'd appreciate any thoughts
> or suggestions.
First of all, eliminate turbulence. Allow some time for the telecope
to coold down (at least 1 hour). Make sure there are no sources of
heat creating turbulent air in the sourrounding, such asphalt,
chimneys, etc. AFTER that has been taken care of, check collimation of
the scope.
pej
--
Per Erik Jorde
tony_f...@yahoo.com
> I have a 12" Meade LX90 just outside Las Vegas. Light pollution is a
> problem, but I don't think a major one.
In addition to what other people have said, if you're just outside Las
Vegas, then light pollution is a genuinely huge problem for you.
Nonetheless, you should be able to see a few stars in M13 through a 12-
inch telescope.
- Tony Flanders
Dennis Woos
> that I think should be distinguishable. I'd appreciate any thoughts
> or suggestions.
>
It sure sounds like you have an optical problem. Even though a laser
collimator is not the best tool for SCTs, in this case it would give you a
quick and easy indication of your optical alignment. If that is wildly off,
then I would check if either the secondary mirror (more likely) or the
primary mirror are not being mechanically well supported, e.g. are loose,
shifted, etc.
Are you a member of your local astro club? There will be folks there that
can help you to diagnose the problem(s).
Dennis
Dennis Woos
<tony_f...@yahoo.com> wrote in message
news:084644f8-a182-423b...@y71g2000hsa.googlegroups.com...
While I agree that light pollution is a major problem, I think I have had
better views of M13 than those described with much less aperture from just
outside of NYC. I have to believe that some severe optical problem is the
primary cause.
Dennis
Havr...@aol.com
I have a 12" Mead and with a 25mm ep M13 looks like a street light
Havr...@aol.com
I should have added that I live just outside of Philadelphia
Bob Feduniak
clear images of jupiter, saturn, and their moons and that individual
stars down to around 5.0 magnitude appear as points, as they should.
Does this suggest that collimation might not be the problem, or is it
a problem that tends to show up mostly in the deep sky arena?
Bob Feduniak
VicXnews
6493e5...@x16g2000prn.googlegroups.com:
Bob...I've lived in Henderson for 31 years...I use to shoot with TechPan with
an h-alpha filter and a 10" LX200(180m hand guided exposures) so I know about
the light pollution....
you should be able to resolve M13 easily...check your collimation....is this
a new scope?
somebidy at LVAS should be able to help...
http://www.lvastronomy.com/
VicXnews
b825c8...@o4g2000pra.googlegroups.com:
Bob...ask someone from LVAS to look through your scope...
http://www.lvastronomy.com/
Vic in Henderson
Dennis Woos
Given this info, you can easily test the collimation by (very, very
slightly) defocusing a bright star at high power (300x or more) and
verifying that the diffraction rings are concentric. You need decent seeing
and cool down, but light pollution/moon won't matter. If the rings are not
concentric, then you need to adjust the secondary to make them so. This is
not rocket science, but you should do a Google search on "collimation sct".
Here are two other ideas. 1) Observe with other folks, and compare your
views to theirs. A decent 12" SCT should provide great dso views, at least
as good as scopes with less aperture. 2) Make sure your eyes are healthy and
your prescription is working.
The last time I looked through a Meade 12" SCT (last summer), the view was
awful. In fact, I think it was M13, and light pollution was not a factor. It
had to be the result of some optical problem(s).
Dennis
Rick Evans
"Dennis Woos" <dpw...@gmavt.net> wrote in message
news:xNydnd8envvFk3PV...@posted.greenmountainaccess...
I also agree. And, while Las Vegas is the light pollution capital of the
world it's
air is also more desert transparent. I have no problem resolving M13
with a
Meade 5" refractor outside champion light polluter Boston.
I reiterate, collimate!
Bob Feduniak
consensus suggestion, I checked my collimation, and it is terrible--
worse than any of the examples of poor collimation shown in the
"collimate SCT" websites. Hopefully, I can fix it in the next few
days.
BobFeduniak
Dennis Woos
This is good news, as you should be able to correct the problem in an
evening. Once you get the hang of it, collimating your scope will be a
matter of spending a couple of minutes. I think that most of the SCTs I have
observed with need collimation, and I also think that most of the owners had
no idea that that was the case or how to do it. Every time I hear or read
that a negative of Newtonians (e.g. Dobs) is that they need frequent
collimation I cringe, as this implies that SCTs don't, which is not true.
They do lose collimation, though I don't know how frequently or how this
compares to Newtonians. However, if I had one that I was transporting in a
car I would check my collimation as often as I could, and be prepared to
adjust it if required.
Dennis
Dennis Woos
Don't neglect to make sure that your diagonal isn't contributing to the
problem.
Dennis
lal_truckee
If your scope doesn't have them already, "Bob's Knobs" make it much
easier to collimate, which leads to regular "touchup" collimation at the
start of sessions (if needed after a quick de-focus check,) and better
overall viewing ...
Dennis Woos
Plus the added benefit of not having to mess around near the corrector in
the dark/cold with screw drivers or allen wrenches.
Dennis
bmo
Bob,
I know that there are laser collimators for SCTs. Although my
experience with them is limited to newtonian telescopes, I believe
getting a <a href=”http://www.lasercollimator.net”>laser collimator</
a> will best resolve your issue. In addition, they make focusing and
diagnosing focusing issues a much easier task. For example, if you
knew your scope was collimated, how much less frustrated would
diagnosing your current problem be?