New XT8 is perfectly crisp without having been collimated. Should I still do it?

[MKHACHFE]

Hi all,

My brand new XT was assembled today and taken out for the first time this evening. I let it cool down for an hour, but even before that, the view of the Orion Nebula, Sirius and Mizar and its double (gap clearly and cleanly visible) were all crystal clear. I was expecting to have to collimate the tube to get the best view, but this seems perfect. No aberration, no fringing, everything pin sharp through the supplied 2.5mm Plossi. 

So, my question is this..does this mean i am lucky and the scope doesn't need to be collimated? I cant imagine the view being any sharper or better than it is to be honest. But i am a newcomer to telescopes and i thought i would ask the experts. That's you! 

 

Cheers,

 

M

[vlaiv]

I'm going to guess here, but that point is misplaced in focal length of plossl? You actually have 25mm Plossl as opposed to 2.5mm one?

If I'm right in my assumption, then the answer to your question would be - I don't know

Your scope is pretty well aligned as is, but with such low power eyepiece it would be hard to tell if you need additional tweak for best performance. In order to check for that, you need to use high power eyepiece - something like 5-6mm or longer focal length eyepiece barlowed x2. When looking with high power eyepiece - point your scope to relatively bright star. If your XT8 is non tracking (and I'm assuming it's XT8 dob that is not motorized - quite a lot of assumptions on my part? ) - best star for this would be Polaris - it will not drift out of view. Next you do a slight defocus - just enough that star is not point any more but turns into small concentric circles.

It should look something like this:

If you "over do it" - it will turn into a doughnut of light and you won't be able to see individual rings inside. These rings are important - if you place your star at the center - and defocus it to observe rings - with perfectly collimated scope they should be concentric. If they are not, and resemble something like this:

Then you need to adjust collimation a bit.

Mind you that distortion in rings are not important - they are consequence of atmospheric turbulence. It is spacing of the rings that is important - they need to be concentric.

 

[rl]

If it works, don't fix it!

Taking screwdrivers and allen keys near lenses just opens up the opportunity for accidents. Got the T shirt....

If it star tests well, with nice round fringes either side of focus, and concentric diffraction rings at high magnification in focus with most of the light in the central Airy disc I'd leave it. Just remember what it looks like properly collimated so you can recognise miscollimation as and when it will surely arise. There will be plenty of opportunity later, after it's had a couple of knocks, for messing around with the dark arts...

Just enjoy the views....

[Buzzard75]

I would at least check it. Won't cost you anything other than a few minutes. I'd recommend doing it during the day when you can actually see what you're doing though and to familiarize yourself with the process.

It's extremely unlikely that a freshly assembled telescope or one that was just taken out of the box is perfectly collimated. Possible, but not likely. It may be that it's just good enough for visual observation, but it may not be PERFECT. If it's good enough and you're happy with it though, I wouldn't mess with it. I tweak mine from time to time to get it as perfect as I possibly can, but on the night of our club events, I just do a quick collimation with the laser and call it good enough.

[Louis D]

I would pick up a Rigel Aline to easily check the primary's collimation, assuming it is center ringed:

[MKHACHFE]

Thank you all for the replies. Yes, it is quite a low magnification. Still, seems pretty darn sharp to me. I have been a 3D animator for 25 years and my eye is good at spotting even a hint of blur insets is an image. That being said, I could be wrong of course. 

I think the view through my eyepiece is sharp as a tack, but maybe I'm wrong. I'll take head of all the advice given and decide tomorrow whether to tamper with it. 

To be honest, I would like to learn how to collimate my scope, so it's probably worth trying. I was just curious what the likelihood it was perfectly collimated from the get go was. 

 

Cheers

[MKHACHFE]

2 hours ago, vlaiv said:

I'm going to guess here, but that point is misplaced in focal length of plossl? You actually have 25mm Plossl as opposed to 2.5mm one?

If I'm right in my assumption, then the answer to your question would be - I don't know

Your scope is pretty well aligned as is, but with such low power eyepiece it would be hard to tell if you need additional tweak for best performance. In order to check for that, you need to use high power eyepiece - something like 5-6mm or longer focal length eyepiece barlowed x2. When looking with high power eyepiece - point your scope to relatively bright star. If your XT8 is non tracking (and I'm assuming it's XT8 dob that is not motorized - quite a lot of assumptions on my part? ) - best star for this would be Polaris - it will not drift out of view. Next you do a slight defocus - just enough that star is not point any more but turns into small concentric circles.

It should look something like this:

If you "over do it" - it will turn into a doughnut of light and you won't be able to see individual rings inside. These rings are important - if you place your star at the center - and defocus it to observe rings - with perfectly collimated scope they should be concentric. If they are not, and resemble something like this:

Then you need to adjust collimation a bit.

Mind you that distortion in rings are not important - they are consequence of atmospheric turbulence. It is spacing of the rings that is important - they need to be concentric.

 

Thank you for the in depth reply mate. And yes, I meant 25mm..oops ?

[cletrac1922]

If just using at home, you will never need to touch the collimation

I am out 2 or 3 times per month with my club doing presentation in schools, scout/guide groups

Very rarely need to re-collimate  my 10" SW Dob

I use a laser collimator 

John

 

[Carbon Brush]

If the views look good. Leave alone. Enjoy the views.

If collimation needs to be looked at, then it will be obvious when you cannot resolve high magnification on nights when the sky should allow it.

Hope this helps, David.

 

[MKHACHFE]

A belated thanks to everyone for the replies and advice.