1st collimation question?

[knobby]

Hi all, thanks for reading...

I've dabbled in collimation but never really had much confidence in the outcome.

my main issue is that when I make the secondary look round and centred under the focuser... After the next step of adjusting the secondary to see the primary clips... The secondary is now... Well, not as it was but quite drunk looking.

is this wrong or inevitable?

thanks

[Scooot]

Hi knobby are you blocking out the primary when you centre and round it in the first place? If you are, when you look at it through the cheshire, does the cheshire encircle it correctly? If so it sounds like everything's normal.

[Moonshane]

sounds like you are looking at the primary reflection not the secondary edge?

maybe my guide will help?

http://stargazerslounge.com/topic/197640-collimation-and-star-hopping/

[knobby]

Cheers chaps... Yep, I use coloured card to block reflections, it all looks fine until I adjust the secondary to show the primary clips...

I'll have a read through your guide Shane, thanks

[Mr Flibble]

Might be rotational error? If so it maybe worth slackening off the three tilt adjusters, rotate the secondary slightly, and then re-tighten the tilt adjusters and line it up to the primary. If its worse than before repeat the procedure but rotate in the opposite direction. If its better keep rotating until the secondary appears round when its lined up. Hope that helps.

[sbooder]

Quick question.  When you get to phase 2 tilting the secondary, is the reflection of the primary doughnut at an extreme edge of the image in the Cheshire before you tilt the secondary?

[wookie1965]

If you can post a picture and let us take a look at it.

[ronin]

I will ask a different question of you:

Are you collimating the mirrors and focuser and checking that the image of the secondary and primary is as expected, or are you altering/adjusting things to get the image of the secondary/primary that you expect.

To me there is a difference.

Collimation is a mechanical alignment of the componemts.

The primary question I would have is:

Is your primary mirror flat/orthoginal in relation to the optical axis of the scope, then is it central to the same ?

Without knowing that this is the state of the primary then I suspect that good collimation is not possible.

[sbooder]

I will ask a different question of you:

Are you collimating the mirrors and focuser and checking that the image of the secondary and primary is as expected, or are you altering/adjusting things to get the image of the secondary/primary that you expect.

To me there is a difference.

Collimation is a mechanical alignment of the componemts.

The primary question I would have is:

Is your primary mirror flat/orthoginal in relation to the optical axis of the scope, then is it central to the same ?

Without knowing that this is the state of the primary then I suspect that good collimation is not possible.

This is what I was thinking.  If the primary is at an extreme angle to start with this would produce the problem in the secondary.

[knobby]

I'll try to get some snaps over the weekend, cheers all!

[Scooot]

This is what I was thinking.  If the primary is at an extreme angle to start with this would produce the problem in the secondary.

I hadn't thought of that, it's a good point. So if this was the case, presumably you'd adjust the primary to move the mirror clips into view?

[Moonshane]

surely no matter how far tilted the primary is, the secondary can still be aimed at the optical centre? as mentioned in most guides, this process can be iterative if well out to start with and it may need you to go back and forth a couple of times. mirror clips are a red herring when it comes to collimation. if a scope does not have clips it can still be collimated, you just need to centre everything - I use the centre donut and rarely refer to the clips.

the primary should always be the last thing adjusted.

[sbooder]

surely no matter how far tilted the primary is, the secondary can still be aimed at the optical centre? as mentioned in most guides, this process can be iterative if well out to start with and it may need you to go back and forth a couple of times. mirror clips are a red herring when it comes to collimation. if a scope does not have clips it can still be collimated, you just need to centre everything - I use the centre donut and rarely refer to the clips.

the primary should always be the last thing adjusted.

You would think so, but no! if the primary is really at an acute angle it affects the view in the secondary of the clips....but it does have to be an extraordinary tilt on the primary to produce this effect.

But I agree that clips are not a good point of reference for the most part.

I no longer worry about the clips when using the Cheshire/sight tube combo for the secondary anymore because I now use a Black Cat Cheshire for the primary and after setting the secondary with the sight tube I find that the clips are where they should be in the view through the Black Cat Cheshire.

And the proof is in the pudding because I am tracking Saturn at the moment and they are the best views I have had in over 10 years, this using the method outlined above for the first time.

Who needs lasers?

[Moonshane]

I suppose sometimes we tend to skip over things that we do without thinking. e.g. my first adjustment for a new scope is often to tighten all primary adjusters as hand tight as they go and then back off by about a turn. this ensures your primary is approximately orthogonal (unless very poorly mounted) before you start.

[lensman57]

I suppose sometimes we tend to skip over things that we do without thinking. e.g. my first adjustment for a new scope is often to tighten all primary adjusters as hand tight as they go and then back off by about a turn. this ensures your primary is approximately orthogonal (unless very poorly mounted) before you start.

The best thing that I did when attempting to collimate my Quattro 8s was to make sure that the primary support plate was at the same distance from the back of the scope at the adjusters locations. This made sure that the primary was atleast orthogonal to the tube. Although the collimation is not perfect yet the last session produced less ugly stars than before, so yes I think making sure that the primary is the centre and orthogonal does matter.

A.G

[Moonshane]

it certainly matters more for imaging that everything is straight and aligned properly.

[knobby]

Thanks all ... I've read and digested all your ideas, going to have another crack tonight.

I think that it's a case of balancing the 'getting it to appear round / under focuser tube' and the 'pointing accurately at the primary'

I seem to be getting one right then messing it up by doing the other!

Ta

[knobby]

OK... Not perfect but its the first time I've ever had the Cheshire and the laser agree with each other :-)

The image of the laser return is actually with the laser loose in the holder and held slightly off to illustrate the red dot... Its actually bang on in the hole (but that would have been a naff picture :-) )

Just waiting on a star test.

thankyou all again for your help

[wookie1965]

Looking at your pictures i would be very pleased if i was collimating my scope and got it looking like that great job.

[knobby]

Thanks again chaps :-) spent 20 minutes last night staring at Saturn through 5mm (240 x) saw banding on surface and glympses of cassini ... Definitely an improvement, star test looked much more concentric too.

happy man!