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Best Collimation Tool for an SCT?

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#1 Brian L

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Posted 10 March 2010 - 04:28 PM

For me, it's pretty hard to beat a star...the price is right also. It's a bit of an iterative process that gets tiresome going back and forth between the EP and the corrector to dial in the collimation. I've never tried a collimation tool, but I've heard some say they aren't very effective because of the folded light path of an SCT. Wondering if any CNers out there have a different opinion and would recommend a specific collimation tool that is useful.

#2 Peter in Reno

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Posted 10 March 2010 - 04:35 PM

This might become the best:

http://www.hotechusa...tegory-s/23.htm

Not yet available but should be very soon. It might cost over $400!!!!

Peter

#3 bcuddihee

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Posted 10 March 2010 - 04:36 PM

A star around 45 degree up, good seeing conditions, a well cooled scope and a narrow fov ep, plossl or ortho giving around 400x in your scope.
Oh, and did I mention practice and patience.
bc

#4 Joe Lalumia

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Posted 10 March 2010 - 05:23 PM

This page may also help you:

http://home.comcast....Collimation.htm

Easier with two people! :) OR a web cam and a laptop.

Joe

#5 Compressorguy

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Posted 10 March 2010 - 06:53 PM

I am in no way an expert on the matter but do own a 10" LX200GPS scope. It has Bob's knobs on it which I have found very useful the 1-2 times that it has ever required collimating and even then it only required 1/16 to 1/8 turn. I've owned it for about 2 years now and it's rolled in and out on casters each use. Maybe this is one of the few that holds collimation well. I agree that a star is the best tool and would think that a supplemental tool such as a laser would only be beneficial for gross misalignment or as a check in the daytime. For me I'll stick with stars, they haven't let me down so far.

BTW, that's a great collimation guide. Thank you for sharing this with us. You all are so helpful!!!!

BTW-W, I have collimated my 10" Cave reflector, the rear primary mirror adjustments are at least 5 feet from the eyepiece, with a webcam and lap top and must say that is the only way to do it!!!

#6 Brian L

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Posted 10 March 2010 - 09:09 PM

I've had Bob's knobs on all my SCT scopes- without a doubt the best $20 investment one can make in the hobby. Just wondering if any of the SCT laser collimation tools are worth their salt.

#7 Rusty

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Posted 10 March 2010 - 10:43 PM

I assisted in testing the Digi-Tec (now discontinued) Laser Collimator. I fashioned a couple of accessories to ease the process, but even after I got them done, it was still a pain to use.

I use Bob's Knobs and a star.

#8 gnowellsct

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Posted 10 March 2010 - 11:12 PM

It's obvious: the Sheer Genius Collimation Device.

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#9 gnowellsct

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Posted 10 March 2010 - 11:12 PM

The Sheer Genius Collimation Device in action.

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#10 gnowellsct

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Posted 10 March 2010 - 11:14 PM

Scientific discourse on SCT collimation

sheer genius and bad seeing

#11 Tom Masterson

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Posted 10 March 2010 - 11:16 PM

I used to recommend a star as the best method but I've found a planet works even better. As you approach focus you'll see the planet's disk surrounded by a fainter disk of the out of focus light. This outer disk should shrink down evenly around the inner brighter disk. If you are off even the slightest you'll see the outer disk shrink down off center. The beauty of this is it works in bad seeing where the shrinking out of focus disk of a star is smeared by turbulence. When seeing is good, its fun to see how collimation effects the visibility of planetary details.

I use Bob's knobs too.

#12 astrovienna

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Posted 10 March 2010 - 11:55 PM

If you've got a webcam and you're equatorial, the best collimation tool by far is Metaguide. This works by stacking live images on the fly, giving you a good Airy disk even in poor seeing. It gives instant feedback, it shows which way the star needs to move so you know which screws to turn, and it recenters the star for you. And it's free. (Thanks, Frank!)

Kevin

#13 David Knisely

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Posted 11 March 2010 - 12:21 AM

For me, it's pretty hard to beat a star...the price is right also. It's a bit of an iterative process that gets tiresome going back and forth between the EP and the corrector to dial in the collimation. I've never tried a collimation tool, but I've heard some say they aren't very effective because of the folded light path of an SCT. Wondering if any CNers out there have a different opinion and would recommend a specific collimation tool that is useful.


Yes, I would have to agree that a simple star works the best. Even under non-optimal seeing, the overall appearance gives me enough to get the collimation on-target. I just point the scope at Polaris and a couple of minutes later, the scope is spot-on and ready for use. It is cheap, doesn't need batteries, adapters, or projection screens, and, most importantly, it is never wrong. Clear skies to you.

#14 David Knisely

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Posted 11 March 2010 - 12:26 AM

I used to recommend a star as the best method but I've found a planet works even better. As you approach focus you'll see the planet's disk surrounded by a fainter disk of the out of focus light. This outer disk should shrink down evenly around the inner brighter disk. If you are off even the slightest you'll see the outer disk shrink down off center. The beauty of this is it works in bad seeing where the shrinking out of focus disk of a star is smeared by turbulence. When seeing is good, its fun to see how collimation effects the visibility of planetary details.

I use Bob's knobs too.


Now that you mention it, a planet like Saturn works particularly well. I recall one Nebraska Star Party a number of years ago when during early twilight, a friend of mine's 8 inch "orange tube" Celestron was out of collimation. He was a little frustrated with it, so I pointed the darn thing at Saturn and after a few tweaks, the image improved nicely and the scope was spot-on. My friend just looked at me incredulously, as if I had performed some feat of magic. After that, I thought about putting a sign on myself saying, "I collimate for food/drinks/conversation". Clear skies to you.

#15 bluedandelion

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Posted 11 March 2010 - 01:10 AM

Has anyone used the Hubble Optics artificial star? I've always used stars but was considering getting one.

Would gives me a reason to pull out the scope on winter evenings.

Ajay

#16 BSJ

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Posted 11 March 2010 - 08:23 AM

I use the Hubble Star with my C6. Works for me.

Although, I have to wait till dusk to see the stars. It's too dim to see in broad daylight.

#17 Brian L

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Posted 11 March 2010 - 09:21 AM

Very clever use of a stick. One of the most important lessons over the years is the following; "what is good enough is often best". Once in a great while there is an innovation that is revolutionary, but people have been star collimating scopes for as long as there have been scopes in need of collimation. It is nice to use an artificial star because it doesn't move. I built one out of a white LED, some shrink tubing, and a stretch of fiber optic cable spooled up in a project box. I set it up across the street about 150 yards away and I can collimate without having to worry about tracking. It's plenty bright enough and I can do it on a cloudy day.

#18 reddog15

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Posted 11 March 2010 - 02:20 PM

The Sheer Genius Collimation Device in action.

Real nice to see others use a thermal blanket,I dont mean to high-jack but all SCT users need to know the benifit of this,or collimation will not be within reach if you do not stabilize tube currents

#19 gnowellsct

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Posted 11 March 2010 - 03:47 PM

The Sheer Genius Collimation Device in action.

Real nice to see others use a thermal blanket,I dont mean to high-jack but all SCT users need to know the benifit of this,or collimation will not be within reach if you do not stabilize tube currents


I actually stopped using the thermal blanket. No diff.

Greg N

#20 gnowellsct

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Posted 11 March 2010 - 03:53 PM

I just point the scope at Polaris and a couple of minutes later, the scope is spot-on and ready for use. It is cheap, doesn't need batteries, adapters, or projection screens, and, most importantly, it is never wrong. Clear skies to you.


Polaris is also my #1 choice, but in an international group, some caveats are required. First off, as you get farther south, the scope will become more progressively horizontal, and mirror weight on the edge (and slight mirror movements in various designs, such as slings) will affect the collimation process. So it may be necessary to use Polaris for the first step and then dial it in on a star that is higher up.

In this sense, it is in fact "An SCT thing" since most SCTs have drives, due to market forces. I think it would be frustrating to use any star except Polaris for collimating if one does not have a drive. You have to be at high magnifications for collimations (well not super high, but maybe 35x per inch of aperture or greater depending on seeing) and then the star is shooting off to one side and you have to center it, etc.

The other night I defocused on Saturn and watched it break up into six pieces (and reassemble) so all I can say is that I'm not sure it always works. But using Jupiter's moons is an established trick of the trade for dialing in best performance: by definition you've got the best collimation for that tilt of the scope.

regards

Greg N






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