How's the collimation?

[matt]

Guys.

Took a lead from Dennis and decided to capture an avi of a star test with my 9.25 tonight to check my collimation.

If it looks a little "earthy" it's because I used antares to perform the test. Hence the browny/red colour.

I can see from the final registax image that the collimation is almost spot on. Could do with a very minor adjustment. Move central obstruction down and to the right, which would see the airy disc shift up and to the left to a perfectly centred position.

I think that's right?

This image was taken with the ToUcam in a 2.5x Powermate for approximately 1175x

[Robert_T]

looks pretty close to me Matt.At this mag you should be closer to focus to pick up collimation error better - that is smaller rings:)

[Robert_T]

by the way Matt I'd be calling the seeing as pretty good based on that image, I've taken avis of stars like this before and rarely do the rings show up so fine... maybe a 6/10 or better?

[matt]

Rob

Had the focus further out to make the outside and inside rings line up with the CCDTools reticle rings.

It helped me judge the concentricity of the rings.

Don't know about the seeing being a 6. There's plenty of twinkle out there tonight. Jetstream looks fairly solid.

I think the registax and processing did a lot for the image:)

Think you might be exaggerating the seeing here coz the seeing at your place at the moment is so typically Canberran!!!

[asimov]

Ah! Thats close enough to perfect you wouldn't notice the difference in an image anyway!

Well done.

[matt]

Thanks John.

That really makes me feel happy to hear that.

You know how collimation can become such a fixation and how you worry sometimes whether you've got it right and if it might be holding you back.

Having never owned an SCT up until Xmas last year I'm still finding my feet.

Cheers

[asimov]

Yes Matt, I certainly know all about that fixation you mentioned. ;) Me being me...I'm gunna make a point of purposely putting the SCT out of collimation & firing off a few to see the difference between good & bad collimation. I've seen the pictures on the internet; but I'm the type that needs to see it first hand. I want to know how far out it can be before it becomes an issue in high magnification photography.

[matt]

Interesting John.

I'll be very keen to see your results.

[asimov]

That damn fixation gets me everytime actually!! Only last night when I dropped in the 2X barlow/diagonal/didgeredoo extension tube...& then had trouble getting focus....I stood back & thought "hmmmm I wonder if collimation ISSS really on the money!??"

I almost had to physically restrain myself from grabbing the damn screw driver & having a tweak! I KNOW it's on the money, damn it! :rofl:

Crap seeing has a lot to answer for! :lol:

[asimov]

Rob has a point though. You need to take it closer to focus to really be able to tell if it's as good as possible.

[matt]

Will do.

It's really not very far out of focus now though, and you lose rings the tighter your focus.

And what benefit is there of being a smaller diameter with more compressed rings and image?

[asimov]

http://legault.club.fr/collim.html

This will explain it better than I can. :)

My collimation is about the same as yours...yes, I use Antares a lot too. Does my collimation look ok ? ;)

[Robert_T]

doh :doh: , that would be it:P

[matt]

John

I've read that page many times.

It doesn't, however, make any mention of the diameter of the star test for an SCT ie how many rings you need for the test to be effective.

Obviously, those star test examples are "idealised" graphic demonstrations and not actual star tests (how they appear).

But I'll record another antares avi with the out of focus image a little closer to focus and more compressed to see what it reveals.

By the way, just in case I'm missing something, what am I looking for in your screen capture of processing jups?

[Lester]

Hi Matt,

Collimation like that image of Antares, I would say what ever you do


DO NOT TOUCH IT!

You will not see the difference in the focussed image. Its called splitting hairs, chasing rainbows. But if you gotta do it to put your mind at rest then because its a free world, go for it.

As a well known prophet (who lives down the road) once said. Seeing rules.

[matt]

Indulge me Lester...

despite the sage wisdom of your beloved guru:P

Who by the way, shares a self-confessed fixation for collimation perfection!

[[1ponders]]

Matt, collimation is a bit like seeing in some respects. By that I mean if the seeing is only mediocre then having your collimation out a bit isn't going to make a hell of a lot of difference. The better your seeing the better your collimation needs to be to make the most out of it. I agree with what has been said before that you need to use less out of focus to judge correctly, though from looking at your image personally I would be trying to tweek that as you said, to the right and down.

It's also very important to have the image/star as close to center of your chip when judging collimation as you can get it. Are you collimating with or without a diagonal?

I've found a pretty good estimate of accuracy of collimation is if the star is flaring out one side more than the other. If it is then you are not collimated yet. On nights of poor seeing I will sometimes use that flaring to judge collimation if I can't get rings. If I can get the flaring even around the star then I should be pretty close to collimated. Certainly good enough for the conditions. In fact in those sort of conditions I will probably be saying, "what the hell am I doing out here wasting my time :doh: "

[[1ponders]]

Also do you suffer from a "Blue" rim on your images after you process, or when you're imaging is one side showing blue flaring? I've found that can also indicate a collimation issue, but not on all nights it seems to depend on the humidity at the time.

[matt]

Cheers Paul

And no, I'm not using a diagonal when collimating. That's a lesson I learnt a looooooong time ago;)

[asimov]

The Jupiter/registax screen shot was just my way of saying "my collimation is NOT perfect, but I managed to capture this bloody shot, does it look ok to ya?"

Happy with Lesters last jupiter efforts? I collimated his scope too...well we both did really :)

[Lester]

Sometimes its in peoples nature to tweek and tweek and tweek and tweek, but all that tweeking would make me giddy, unless there were real noticeable results.

My 8" Celestron SCT has never been recollimated in over 30 years and the Guru has checked it and was satisfied. That scope has been half way across the country via Australia Post twice and back and still collimation is spot on.

I think why some are conserned about collimation and cleaning optics is that deep down this imageing thing is like a competition and someone gets good conditions and flukes it, while others are looking to the steroids to do the work.

[[1ponders]]

efinately not pickin', they all look good to me, 'specially seeing as they are the only Jupiters I'm getting to see atm:rain: :cloudy: :sad:

The blue rim I'm talking about show's up on the left side in your image Asi, and I found it a real pain to try to deal with at times. I'm talkin' fractional turns of the ol' allen key to ge it right. And some nights I jus' can't get it. The more humid the atmosphere the harder it seems to be.

[Lester]

Yea you tell em Asi, I helped. :party: (otherwise they won't believe me):cool:

[matt]

Who's to say who's right or wrong Lester?

And didn't many a wise man once say "we learn by doing"???

I've never owned an SCT before so it's all a learning curve. I've also spent thousands of dollars on kit that I'm trying to get the best performance out of.

I live in an area which is quite adversely affected by seeing, so I'm working flat-out to make sure I've got everything under control which is in my control.

As for being competitive etc.... well, that's not for me.

I'll leave that to you and John and your on-going 9.25/ 14 inch shootout of which we read sooooo many regular updates/ thoughts and never pass comment about its validity:)

[asimov]

Lester turned the scews for me, & he did a great job too!:rofl:

I know the blue ring in question Paul. I play with the wavelett filter (not to be confused with the waveletts themselves here) to tweak it out, & if I can't I leave it there. :)

[matt]

Wow! Asi

I just noticed the wavelets in your registax screen capture.

Slider 6 and 5 are fully cranked!!!!!

That's what I call HARD processing:scared:

[asimov]

Correct Matt :) theres no 'right or wrong here' I'm always looking for that perfection, that ultimate collimation...just one more tweak of that screw! And now that my mate Paul has mentioned the dreaded blue ring, I'll be getting on a roll & trying to tweak that out now!....THANKS MATE!!!! :mad2: :rofl:

Hey you could question the validity of the games Lester & I play...:P

[asimov]

Yeah, I like things fully cranked Matt :)

[matt]

The validity issue wasn't directed at you John and I enjoy the comparisons between the 2 scopes. Just as I enjoy posting about the minute intricacies of SCT collimation and will continue to do so.

Looking forward to your further "tweakings" in Collimation Land, unless your mate talks you out of being so nit-picky and pernickety:lol: