Secondary holder is drunk ???

[Shawn]

Collimating the scope last nite, not really first light, more like just seeing how close it was after travel, needed very little in the way of adjustment about 1/8 turn on one and a wee smidge on another to get perfectly concentric rings both sides of focus, with barely discernable mirror flop, even with the lock off. But when looking down the business end the reflections are far from concentric, the secondary looks crooked and the reflection of the secondary in the primary is not either, I kind of get lost in the reflections at least I think thats what Im looking at... Anybody ?????
:shrug:

[asimov]

If you have perfectly concentric rings each side of focus in a star test, forget what you see down the business end I would suggest.

[Shawn]

Great, thank Asi .Sort of worrying tho, Ive trolled the net looking for info on it, to no avail, read just about every page on collimation out there, My eyes seem to be telling me that that the optical axis is not dead straight. ,,,this may or may not cause problems with allignment,,,I wouldnt know..It getting tough to get my head around.

[leon]

Yea mine looks a bit wonky when i look at it, but stars are crisp, and in focus.
so, if it aint broke dont fix it i say.

[Lester]

Hi Shawn,

If you are getting concentric rings around out of focus star when it is centred in field of view, and using high magnification ie. 5mm eyepiece. I would ignore what you see when looking down the tube from the corrector end.

Pleased to hear that you have almost no mirror flop, but was that also at high magnification. My LX200 14" at 1200x = when imaging Jupiter the image will move 2 fields of view, on the laptop from one side of focus to the other. But at say 200x it would be almost nothing. I gather that you will be mainly using your scope on DSOs, so you may not have tested your scope at such high magnification.

[Shawn]

Thanks Leon

Lester only have 9mm, what I meant by mirror flop is movement in the rings when balance is shifted from East to West. but yes with the 9mm nearly a whole feild of view on focus in to out. that movement not present with general slewing around, did I get my terminology wrong , ?.. The whole experience has resulted in contradictory observations. When you squiz down the busy end of your 14" are all the reflections concentric with one another...

[Lester]

The busy end I presume is the corrector end. I have never looked much down that end, because if collimation is good at the eyepiece end, I am satisfied.

[Shawn]

Me neither, I just noticed it and thought,,,thats odd. First instruction in the book, "where to put your eye",:lol:

[Hitchhiker]

Shawn, I agree with what others have said - if the rings around an out of focus star are concentric, your collimation is fine.

Looking down the corrector end, you will see all sorts of things depending on where you are looking from.

[Shawn]

Yes the reflections are confusing, but are definately not concentric, unless my eyes need collimating, "thats quite likely" . I think your right, in the words of Leon ,,,If it aint broke dont fix it...

Cheers All

[asimov]

Mine are not concentric either looking down that end (C9.25 SCT) But I take no notice, the proof of the pudding is in the star test. Hope your mind is at ease now Shawn :)

[Lester]

Come on now Shawn,

Please get us some DSOs. After seeing Strikers 10" richy perform, and produce small compact star images, can't wait for the

BIG GUN To pull in a few DSOs.:)

[ballaratdragons]

You will always see the optical train as 'out of wack' when trying to look in the wrong end.

That is because the only place you could see the train line up is where the secondary obstruction is, and you can't see thru the obstruction (unless you are Superman)

[asimov]

You stand at the correct distance so that you can see the reflection of the secondary just fractionally bigger than the actual secondary Ken.

To do this correctly you would use a card with a peep hole in it mounted on a tripod for instance, & keep positioning the card until the exact position & distance is attained. It's on the internet, & this method is used to roughly align after stripping the scope for a corrector or secondary replacement etc.

Edit: Adding article

http://www.mira.org/ascc/pages/lectures/collim.htm

[Shawn]

Ahhhh, guys my mind is at ease,,,And yes the obervatory is on progress, nearly have all I need to those DSO,s. Ill try not to dissapoint:),,

Thanks again

Shawn

[Roger Davis]

The optical axis is not always coincident with the mechanical axis.
The important thing is to optically collimate your instrument.
See:

http://www.kendrickastro.com/astro/pdf/sct_collimation.pdf

[Shawn]

I thought this might be the case, which brings me to another question, If the optical axis in not coincident with the machanical one, how would this affect polar allignment, if indeed it does to any significant degree...:shrug:

[[1ponders]]

Thanks for that link Roger. :thumbsup:

[Roger Davis]

Although the optical axis not coincident with the mechanical axis, it doesn't necessarily mean that it is not parallel to it. If you have drift aligned your scope as the final polar alignment method, then it makes no difference! All axes have been taken into account for orthogonality, otherwise you would not be polar aligned and tracking on an object.

[Shawn]

Thanks a lot for your help guys, got a fair amount of work ahead of me before I can attempt proper allignment, all this is noted and will be recalled upon when I get the beast into its new home...

Again Thanks...