Stars and Collimation

[75BC (Brendon)]

I have a question about collimating.

Do people use a particular / favourite star when collimating / star testing?

I need to collimate my SCT as I’ve replaced the screws and was wondering if any old (or young) star will do. Are some better than others? I’ve read about magnitudes, and using stars near your intended target, but thought there may be a certain star out at the moment that, because of the way it looks in the eyepiece, can give a better result, compared to another.

Peoples thoughts on this will be most appreciated.

[Merlin66 (Ken)]

Brendon,
You need to use the Goldilocks star.....
Not too bright, not to dim, just right!
Not too low in the sky...

[brian nordstrom (As avatar)]

Ken is right. , any of the 3 stars that make up Orion,s belt will be fine just after dark this time of year. .

Just be aware that this type of collimation is very ,very sensitive and remember to use small movements , but once you get it, it will be perfect .

I use this method on my C9.25 and when it is on the view is awesome.

Brian.

[75BC (Brendon)]

Thanks Ken and Brian.

Ken, your mention of the Goldilocks star sounds familiar. I must have read it somewhere. Not that i can remember.

Brian, when you say 'this type of collimation' are you referring to collimating SCT's in general or something else?
I had heard that the 11" is super sensitive when comparing it to the 8" and 9.25".

[Merlin66 (Ken)]

Brendon,
I also have a C11 which I use exclusively for spectroscopy.
IMHO it's no more difficult to collimate than any other SCT I've had.

[The_bluester (Paul)]

Just don't use a double star or you may see some odd results!

[75BC (Brendon)]

Originally Posted by Merlin66

Brendon,
I also have a C11 which I use exclusively for spectroscopy.
IMHO it's no more difficult to collimate than any other SCT I've had.

That's encouraging to hear Ken. I 'am more confident with collimation than I use to be. It took a long time to get my head around it with a dob. Less time collimating = more time observing.

Originally Posted by The_bluester

Just don't use a double star or you may see some odd results!

Funny you should say that Paul. I learnt that the hard way.

[brian nordstrom (As avatar)]

This type of collimation , I mean the star test eg. Using a star,s defocused image to collimate your optics.
Brian.

Originally Posted by 75BC

Thanks Ken and Brian.

Ken, your mention of the Goldilocks star sounds familiar. I must have read it somewhere. Not that i can remember.

Brian, when you say 'this type of collimation' are you referring to collimating SCT's in general or something else?
I had heard that the 11" is super sensitive when comparing it to the 8" and 9.25".

[The_bluester (Paul)]

Originally Posted by 75BC

That's encouraging to hear Ken. I 'am more confident with collimation than I use to be. It took a long time to get my head around it with a dob. Less time collimating = more time observing.



Funny you should say that Paul. I learnt that the hard way.

As did I!, wondered about a bumpy de focussed star until I realised it was a double.

[75BC (Brendon)]

Thanks for clarifying that for me Brian.
Using a star in Orion’s belt should work well for me as it‘s in the darker part of my sky as I’m north of Perth. Point noted on small adjusted as this was one of the things I was doing wrong when collimating my dob until I learnt how.
And am I correct in saying I should wait for a good night for in focus collimation?

Originally Posted by brian nordstrom

This type of collimation , I mean the star test eg. Using a star,s defocused image to collimate your optics.
Brian.

[75BC (Brendon)]

Originally Posted by The_bluester

As did I!, wondered about a bumpy de focussed star until I realised it was a double.

Ha. That's exactly what happened to me. Good to know others make the same mistakes.

[The_bluester (Paul)]

Yeah, I knew not to do it but just aimed at a convenient bright star without thinking about it. Rigel as it turned out. The pup is small and dim but it was enough to make the star image look wrong. A quick check to make sure no one was looking and off I went with a better candidate!

[75BC (Brendon)]

Originally Posted by The_bluester

Yeah, I knew not to do it but just aimed at a convenient bright star without thinking about it. Rigel as it turned out. The pup is small and dim but it was enough to make the star image look wrong. A quick check to make sure no one was looking and off I went with a better candidate!

You're kidding! Rigel was the star I did it with.

Once I realized I thought I'd stop and have a good look though as I've never really looked at many stars / doubles / multiples. Quite beautiful, and it sparked a new area of interest for me.

[75BC (Brendon)]

Thanks to all who replied. Just thought I would update those who are interested.

Had a go at collimating on the weekend. I used Alnilam. As this is a new scope for me (had a 10” dob before and use to collimate during the day) I’m learning how to do this. Spent quite a while turning screws and checking and although it was roughly there, I couldn’t quite seem to improve on this very rough collimation.

Last night I thought I’d have another crack at it. This time I used a combination of Alnilam and Aldebaren. Now I’m getting somewhere. I think I was going wrong by not tightening all the screws. As I have replaced the original ones, they weren’t tight. So this time I only tightened each screw that needed adjusting. My local conditions couldn’t support anything like high mag collimation, so my goal of getting it ready for some really detailed planetary views will have to wait. But it’s getting there now. I wasn’t out there long as I get up at 5am for work (and I need my beauty sleep), but before I packed up I swung over to our old friend Orion and had a look at M42. Looked good. Icould quite easily see the ‘E’ component of the Trapezium at 140x (first time I’ve ever seen it), and I swear ‘F’ was there somewhere teasing me.

I ‘am super impressed with my new setup. When I emptied my bank account on this I was hoping, but honestly didn’t think I would see THIS much difference from my Newt. Can’t wait until I really start stretching its legs.

[Regulus (Trevor)]

I use a cheap Cree torch i got from Aliexpress.
I cover it with foil and put the smallest pinhole in it, and then I set it up about 20mtrs away from the scope (although I read somewhere that 30~40mtrs is recommended).
As an artificial star it's excellent.

Trev

[75BC (Brendon)]

Hi Trevor. I did think of doing the same as don’t like wasting my limited observing time. What put me off was conflicting info I read on the distance you need to do it. I didn’t want to have to take my scope somewhere to give me enough room as it would kind of defeat the purpose. I’ve read some people using distances in the 100’s of metres. If you’re able to do it at 20m, I might give it a try. Thanks.

[The_bluester (Paul)]

I had heard of but never really considered using an artificial star, which I should. If I can make a suitable one I have a good candidate tree around 50M away from where I usually set up that I could attach it to.

Also, it is really worth considering a set of Bobs Knobs collimation screws if you have an SCT and it has normal screws fitted. the ones on the C925 required the use of a small, sharp, pointed screwdriver and the thought of waving that around near the corrector plate in the dark did not impress me much.

[75BC (Brendon)]

Hi Paul. I’d be lucky to get 30m distance without going into a neighbour’s yard which is why I haven’t tried this method.

I did consider Bob’s Knobs but decided not to. Purely personal choice. I used some stainless items instead. I only changed them because when I got the scope and checked collimation it was a bit out. Must have had a bit of a bumpy journey I spose. 2 of the screws were really tight and I stuffed the heads on the originals which are quite soft material.

[The_bluester (Paul)]

I have found the thumbscrew collimation screws really worth having, with a bit of practice (And suitably longish arms) you can tweak one while still looking through the EP, or very nearly so. I found it much quicker as you don't have to be so careful placing a tool for fear of scratching the corrector plate. The worst that you are likely to do is put a fingerprint on it.

[75BC (Brendon)]

There were a few reasons I didn’t go with Bob’s knobs.

1. I have long arms but I still don’t think I’d be able to reach them while looking through the eyepiece on this scope.
2. Some people say they don’t hold collimation quite as well as normal screws. Not much in that one possibly.
3. I suffer many afflictions. A couple being perfectionism, and a severe case of OCD. Having the knobs would just make it far too tempting to fiddle all the time, and like you say Paul, going near the corrector with a sharp instrument is not much fun. Very scary actually. Kinda works the same way as that stuff people paint on their fingernails to help stop biting them. If you don’t like it, you’re less likely to do it.