
Collimation question
#1
Posted 27 May 2005 - 09:57 AM
A friend of mine decided to tweak his collimation last night on his nexstar 8 gps he bought used a while back. It was the first time he had touched the collimation. stars had shown a bit of a flare to one side in focus.
He tweaked at low power and then went to to the mid 400s i think. It definatley got better and he was able to make the rings on one side of focus look pretty good. The moons of jupiter became more point like than they had ever been in this scope.
However. he couldnt really get rings on one side of focus at high power, it was more like a fuzzy blob looking thing. the other side looked ok and it seemed the scope was in better shape than before he did anything.
Anyone have anny suggestions about being able to get rings on one side of focus and only a fuzzy looking roundish thing on the other side of focus??? I know this isnt much information but i thought it might ring some bells with someone. thanks
#2
Posted 27 May 2005 - 03:11 PM
But, inadequate cooling of the optics can have this same effect.
Without active cooling (such as the Lymax SCT Cooler), some modern SCTs, if put in conditions where the temperature is steadily falling, may not show completely equilibrated optics over an entire night (especially the latest versions with carbon tubes).
You did not say how soon after setting the scope up you performed the collimation.
Here's a site with pictures of what I mean. Look down the page to see examples of the aberration you describe: Aberrations in the star test
Of course, no man is an island, and neither is any scope aberration. You likely saw a hodgepodge of seeing problems, spherical aberration, thermal issues, and possible a slightly turned edge. Unless the seeing is exceptional, it may not be possible to identify which, exactly.
As a doctor's oath says, "First, do no harm". Collimating the scope (it sounds like a major improvement was made) did no harm. Only after addressing the thermal issues can he begin to pin down the source of his aberrations (which may be quite minor if the moons of Jupiter were pinpoints).
Let's see what happens the next perfectly still night. Please report back.
#3
Posted 27 May 2005 - 03:27 PM
#4
Posted 27 May 2005 - 04:40 PM
#5
Posted 29 May 2005 - 10:07 AM

I had a similiar problem and scoured the world for an answer. Ended up that my corrector had a finger sized smudge on it.
Good luck!
#6
Posted 30 May 2005 - 12:42 PM
---------------------
Paul
C-9.25 CF XLT on EQ-6 star test results
#7
Posted 03 June 2005 - 06:36 PM
#8
Posted 08 June 2005 - 11:12 AM
#9
Posted 08 June 2005 - 01:23 PM
A bold statement to make, if you also consider larger scopes. I'd *love* to live in conditions where average seeing conditions always supported 800xFor those of you who have never seen the airy disk, your scopes are either not cooled or not collimated.

I can see Airy discs, mind you - but I have to stop down my scope.
#10
Posted 05 July 2005 - 12:41 PM
A bold statement to make, if you also consider larger scopes. I'd *love* to live in conditions where average seeing conditions always supported 800xFor those of you who have never seen the airy disk, your scopes are either not cooled or not collimated.
.
I can see Airy discs, mind you - but I have to stop down my scope.
I've seen Airy disc at lower powers than 800x, try around 300x. It's more of a function of atmosphere conditions than magnification.
#11
Posted 05 July 2005 - 12:46 PM
I've seen Airy disc at lower powers than 800x, try around 300x. It's more of a function of atmosphere conditions than magnification.
The magnification required to see the Airy Disk varies directly with aperture. 300X won't do it in larger telescopes.
#12
Posted 06 July 2005 - 04:17 AM
I've seen Airy disc at lower powers than 800x, try around 300x. It's more of a function of atmosphere conditions than magnification.
Well, you have an 8", and I have a 16"...as I said, if I stop down my scope, I do see Airy discs much more easily.
#13
Posted 06 July 2005 - 07:57 AM
#14
Posted 06 July 2005 - 10:44 AM
#15
Posted 06 July 2005 - 10:51 AM
#16
Posted 06 July 2005 - 10:00 PM