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New Scope, FLR, Help

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#1 jacobmarchio


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Posted 02 February 2013 - 10:33 AM

Hi all,
Yesterday, I went down to Gainesville, Florida to pick up my new (used) scope, a C9.25 on a CGEM mount. Weather looked good, so got first light last night. Just did a quick-and-dirty polar align on CGEM and did a minimal alignment. First impressions: The scope looks good on the outside, with just some dust on the corrector as a result of buying used. The CGEM mount is a BEAST! I've never owned anything bigger than the Orion AstroView (CG-4 equivalent), so this thing is a monstrosity to me.

Unfortunately, I popped in an eyepiece (my lowest power, 25mm is 94x) and attempted to focus. I tried, it's like it just wouldn't focus sharply (even with that nice FeatherTouch dual speed focuser, which came installed). All I would get is... mushy-looking stars. Defocusing a star showed that it might have some collimation issue (check out the attachment, this is straight from the camera). Also, I was having trouble aligning the mount on two stars, as the installed telrad had no battery, and the 50mm RACI wasn't remotely aligned with the scope. Oh, and the scope wasn't fully cooled either. Plus the narrow fov is driving me nuts, I'm used to my 6"F/5 newt.

So I said fine, enough with the C9.25. I went over to my 6"F/5 newt and popped my 25mm and 2.5x PowerMate in (75x) and focused on M42. Aaaah, small stars. But they, too, were seemingly not focusing well. Upon closer inspection showed that the stars were wobbling and waving... saying "BAD SEEING" (which I found odd, as stars weren't twinkling too much at all. And yes, the scope was cooled down). Yeah, it was bad even at 75x. I dropped it down to 30x and was happy.

So, I'm hoping that the soft stars aren't a result of bad optics, or are just normal in an SCT, but were soft because of the scope not being cooled, bad seeing, and possibly off collimation. This is my first SCT, by the way.

Going back to collimation. Like I've said, this is my first SCT. How do you collimate it? How do you know if it's the primary or secondary that needs adjustment? I don't have any collimation tools like a Cheshire eyepiece, just a simple collimation cap that came with my Newtonian. Help?

Thanks in advance!

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#2 Julio



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Posted 02 February 2013 - 11:40 AM

I had a similar circumstance with my C9.25. The stars and Jupiter's moons will appear flared to one side. Stars at high power in focus would not show a clean airy disk and would also flare. After careful and lengthy collimation the stars were round as they should be. However the airy disks were not clean due to seeing. It is much more difficult to see a clean airy disk on a large scope like a C9.25 unless seeing is superb. Collimation on SCT is best performed on a star using a 3 step process, lasers dont work as well as a star and are quite costly for SCTs, look at the last link for collimation. Also ive had nights when my 9.25 took 3 hours to cool down properly, just give it more time leave it out 4 hours or so on a night you plan to collimate and star test.


Also as you have to show much less defocus, as well as showing both sides of focus for the star tests. Read this thread.


And finally collimation is a 3 step process.


If the problems continue after the careful collimation under very good seeing, then you might have other problems.

#3 jacobmarchio


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Posted 02 February 2013 - 05:48 PM

Thanks Julio for your help.

I did a collimation on an "artificial star" of sorts off the sun's reflection on a power pole and a shiny cabinet knob that I set up outside. I think I got it pretty good (luckily they had Bob's Knobs). Will try to view again tonight, but CDS predicts bad seeing, so... will try to keep the magnification low.

#4 stevew


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Posted 02 February 2013 - 09:35 PM

Jacob, your image does indeed show that the scope needs collimating.
But also be aware that an SCT can take hours to reach thermal equilibrium, especially this time of year.
You also may want to invest in a lower power eyepiece. A 32 or 40mm would be a good choice for the C9.25


#5 EFT


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Posted 03 February 2013 - 01:25 PM

You were definitely seeing the results of several different issues coming into play together. The collimation is clearly out, bad sky seeing, bad tube seeing and being use to a much faster wide-field scope.

Collimation is relatively easy (certainly easier than the newt). The only thing adjusted is the secondary. There is not primary adjustment mechanism.

Give the scope plenty of time to acclimate as that will make a big difference in its performance.

The view through the SCT will always be very different than what you are use to with the newt. But it can show you things that the newt can't do as well. A side by side comparison doesn't really work since they are different duty instruments.

#6 jacobmarchio


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Posted 04 February 2013 - 10:04 PM

Took it out on the 3rd. It was stored in an unheated shed. I took it out about sundown, and went through setup and alignment. Only did a polar alignment through the polar scope, next time will have to try a better method of alignment. Even so, GoTos were pretty good, placing object at the edge of my 25mm eyepiece. After alignment, I put the mount in hibernation and went inside to eat dinner and watch the second half of the Super Bowl. After the game, I went back outside for observing. Seeing was pretty bad, again. But I'm pretty sure the scope was fully cooled, considering the time it spent sitting out there. And I think collimation closer, too. Was pleased with excellent views of M42 at 98x. Split Rigel nicely. M81 looked great also. I'm happy :D Can't wait for dark skies and good seeing! :jump:

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