Collimation Accuracy

[deadsimple]

Hi all,

I just attempted my first collimation of an 8" Dob I bought last week. Took me about an hour of fiddling around to figure out what was going on - the relationship between the three screws and the centre screw on the secondary mirror wasn't obvious to me and threw me off track for a while.

Anyway I think I have it all sorted but was wondering how accurate the collimation should be for most purposes? How good is "good enough?"

I've included two pictures of the results of my collimation (sorry for the rubbish quality). First image was done on a tripod with the collimation tool's crosshair in focus so it's a more accurate illustration. Second image was hand-held but has better details in the middle. Is that good enough?

Thanks :)

[GeoffW1]

Hi,

A star test will help you to know this

http://www.iceinspace.com.au/index.php?id=63,206,0,0,1,0

Cheers

[deadsimple]

Thanks for that.

Perhaps if there weren't a thunderstorm above me right now, I may have thought of doing that :)

Guess I was just after a quick rule of thumb for telling at a glance (during daytime) if it's good enough.

[GeoffW1]

Aha,

During daytime is not a bad idea either, saves time. I can't assist you with a comment on your photos because I don't do it that way (I like a barlowed laser) but hopefully others here can.

In the meantime, the attachment to this post has some good diagrams in it

http://www.iceinspace.com.au/forum/showpost.php?p=138988&postcount=18

and also worth a look

http://www.andysshotglass.com/Collimating.html

http://www.schlatter.org/Dad/Astronomy/collimate.htm

Cheers

[GeoffW1]

Hi DS,

So how did you go? Was it OK?

My agenda I admit is to recruit you to the ranks of Barlowed laser collimators. Dead simple, follow with a star test.

Cheers

[deadsimple]

Sorry, I thought I had replied to you - it seems I must have closed the tab before I hit Reply.

Thanks for those links but I had already visited them before (the Orion guide actually came with my collimation tool and it was the shotglass vid that took me from headscratching to understanding most of what was going on).

Anyhow, I tried the (star) unfocus method and the black spot is pretty much directly in the centre of the blur. I still think I can improve things a bit, but in my newbie state I doubt I could visually see the difference while observing. I'll wait till it's out of whack again and attempt a more accurate collimation next time.

Only thing left is to get rid of these clouds :)

[GeoffW1]

Hi Ash,

From what you say your collimation seems quite good.

I am always ready to give you the wisdom according to Geoff :thumbsup: (you should know I have got in trouble here on the forum though :doh: in the past).

I have found the barlowed laser the most efficient after trying every method (not every brand:driving:) there is

Cheers

[deadsimple]

Even taking the primary mirror out last night and putting it back in, the collimation is still mostly good.



The plan for me was to start off with the cheshire/sight-tube to begin with, then move onto laser once I know what I am doing. But .. my webcam is arriving in a couple of days, so I might give the webcam collimation method a go :)

Thanks for the assistance!