just picked up a Meade 2080 F/10, what to check?

[R2D4]

A neighbor had a Meade 2080 they were about to actually toss out so I
got it just before the trash pick up on Tuesday. He said he was getting
rid of it because he's moving and had no time for sales, I gave him $100
anyway which, if it works ok, would be a steal. This appears to be the
F/10 model. With it came 9x60 finder with illuminated reticle,
equatorial wedge, drive and heavy tripod, a couple of eyepieces, drive
controller and power supply. There's also the diagonals for both scope
and finder and 2 to 1.25" adapters. One thing I did find out is that it
is a HEAVY beast, seems heavier than even the 9.25 I used to have on
GC-5. I sold off all my SCT's years ago and was never really going to
return to astro until I saw this giveaway.

Now the question: how do I check this out optically? I look through
the corrector and the primary seems fine, not sure how to see how the
secondary looks. So any advice here would be welcome as well as how to
test resolution, collimate, etc.

There appears to be one thing missing that I sort of need because I
can't see Polaris most of the time and that is the compass that snaps
into the base-- any idea where I can find one or is there a substitute
that will work?

Thanks for any help,
R2

[Chris L Peterson]

There is a wide range of quality with the 2080s. They were really
pumped out back in the 1980s when Comet Halley was boosting amateur
astronomy, and Meade's quality control left a lot to be desired. I'd
start by seeing just how well it collimates (there are online
tutorials providing the details, but essentially you look at a star at
high power, in focus and on both sides, and adjust the three screws on
the secondary mirror). If you're interested in a critical analysis,
I'd suggest you pick up Suiter's book, _Star Testing Astronomical
Telescopes_.

A compass is only suitable for a very rough polar alignment. That may
be good enough for basic visual use. Any compass should do. Why can't
you see Polaris? If it's normally in your sky (you're not too far
south), it's bright enough that you should easily see it under almost
any conditions you'd want to observe.

[R2D4]

On 02/19/2017 12:03 AM, Chris L Peterson wrote:

>
> There is a wide range of quality with the 2080s. They were really
> pumped out back in the 1980s when Comet Halley was boosting amateur
> astronomy, and Meade's quality control left a lot to be desired. I'd
> start by seeing just how well it collimates (there are online
> tutorials providing the details, but essentially you look at a star at
> high power, in focus and on both sides, and adjust the three screws on
> the secondary mirror). If you're interested in a critical analysis,
> I'd suggest you pick up Suiter's book, _Star Testing Astronomical
> Telescopes_.

Thanks. I just found a slightly older version of the book online and
skimmed through it briefly. Unfortunately, with my only occasional good
seeing here (maybe ten nights a year), I may have to do the artificial
star test but this could be problematic for the distances required. I
may just have to check Jupiter, Saturn, or the Moon in the meantime once
I check collimation. I kept a set of Bob's Knobs from when I had
Celestron SCT's several years ago, but not sure whether or not they'll
fit this scope.

>
> A compass is only suitable for a very rough polar alignment. That may
> be good enough for basic visual use. Any compass should do. Why can't
> you see Polaris? If it's normally in your sky (you're not too far
> south), it's bright enough that you should easily see it under almost
> any conditions you'd want to observe.

Sorry, I wasn't entirely accurate here. I can often see Polaris, which
of course I'll use to help align, but I also want to use the scope with
stopped down, filtered aperture mask during daytime to do solar
observing, which was the need for the compass. I believe I found a
compass source, however.

[Chris L Peterson]

On Sun, 19 Feb 2017 10:08:07 -0500, R2D4 <r2...@stwars.com> wrote:

>Thanks. I just found a slightly older version of the book online and
>skimmed through it briefly. Unfortunately, with my only occasional good
>seeing here (maybe ten nights a year), I may have to do the artificial
>star test but this could be problematic for the distances required. I
>may just have to check Jupiter, Saturn, or the Moon in the meantime once
>I check collimation. I kept a set of Bob's Knobs from when I had
>Celestron SCT's several years ago, but not sure whether or not they'll
>fit this scope.

I tried thumbscrews at one point, but frankly, they don't work very
well for good collimation. They just don't give fine enough control,
and they don't let you tighten them down as much as you need. I
suggest using good quality stainless steel hex head screws, and a long
handled hex wrench (at least six inches. You get much more control
that way.

Although it's not a requirement, what I found was the greatest assist
for good collimation is a simple video camera or webcam. You can watch
the star on a screen while you're collimating from the aperture end of
the scope.

[Razzmatazz]

Look at the sun's reflection on a powerline insulator. Do this toward evening when ground air has stabilized. You will see a bright star-like dot, and you can then leisurely collimate the scope. Even if not fully collimated, you can judge the optical quality of the scope by looking at the inside-focus and outside focus Fresnel rings. You will see a bright donut with a dark hole (shadow) in the center caused by the secondary mirror shading. This secondary shadow should look the same on either side of focus, but the most important quality criteria are the roundness of the donut ring when inside and outside focus. If it is oval on one side and flips 90 degrees on the other, then the scope will have astigmatism and will not be ideal for high power planetary views.

Google "testing telescope optics" for more thorough information.

Razzy

[R2D4]

On 02/19/2017 10:29 AM, Chris L Peterson wrote:
> On Sun, 19 Feb 2017 10:08:07 -0500, R2D4 <r2...@stwars.com> wrote:
>
>> Thanks. I just found a slightly older version of the book online and
>> skimmed through it briefly. Unfortunately, with my only occasional good
>> seeing here (maybe ten nights a year), I may have to do the artificial
>> star test but this could be problematic for the distances required. I
>> may just have to check Jupiter, Saturn, or the Moon in the meantime once
>> I check collimation. I kept a set of Bob's Knobs from when I had
>> Celestron SCT's several years ago, but not sure whether or not they'll
>> fit this scope.
>
> I tried thumbscrews at one point, but frankly, they don't work very
> well for good collimation. They just don't give fine enough control,
> and they don't let you tighten them down as much as you need. I
> suggest using good quality stainless steel hex head screws, and a long
> handled hex wrench (at least six inches. You get much more control
> that way.

Any chance you or someone else know the correct size screws needed for
this Meade 2080 F/10 with three screws? Also, should the stainless
screws be the same length as the original?

>
> Although it's not a requirement, what I found was the greatest assist
> for good collimation is a simple video camera or webcam. You can watch
> the star on a screen while you're collimating from the aperture end of
> the scope.

Good tip, thanks.
>