Collimation Confusion

[Entropy]

Hi guys,
Its me again with yet another annoying beginners question. Firstly i need to give a bit of background on my scope as i'm not sure if this is relevant.

I own a Saxon 8" Newt, it had one of those really bad R&P focusers on it, i put up with it for quite a few year, but last year i had enough and i purchased a bintel crayford style focuser. I had some slight problems fitting this focuser to my telescope but with some new screws, some grinding in the screw holes and a bit of frustration i managed to get it focused.

Around this time i also learned more about collimation. I purchased a laser collimator and have had a couple of goes moving the secondary mirror only. Today i have got the guts up to start moving around the primary mirror to see if i can improve this further.

My question is, how important is the focuser's position in the telescope, can any mis-alignment be collimated out?

Also, should i be playing with the primary mirrors position with only a laser pointer? If so what exactly am i looking for with the red dot?

Thanks for your help guys
Scott

[erick]

Hi Scott

First step is to search out the collimation threads here on site. There are several in recent months that will provide lots of information (and probably more confusion as well!).

Follow your laser's instructions. First adjust the secondary tilt until the laser dot is hitting the centre of the primary mirror, then adjust the primary mirror tilt until the laser beam is returning directly back to the laser. Achieving this is not perfect collimation as you'll read in the threads, but it's a lot better than doing no collimation at all.

Eric :)

[DJVege]

Check out andysshotglass.com. The collimation tutorial there is great.

Also, make sure your laser collimator is also collimated.

Also, the focusers position is important. It should be directly above the secondary. You can use a cheshire to check this.

[rmcpb]

Scott,

Don't get too worked up about your collimation, it gets better with practice and we all start somewhere.

If you have not been adjusting your primary then you have not really been collimating your scope.

Now let's start at the beginning.

If you installed your crayford focuser directly onto the tube and have not buckled the tube then it should be OK. The GS crayfords come with the curve for a 230mm tube so it should just bolt straight onto your tube and be aligned.

If collimation is broken down to its essentials then there are three steps:
Centre secondary under the focuser so that it has an even "margin" around the secondary when looking directly at it through the focuser or, even better, through a sight tube like a Cheshire eyepiece. I find it a bit easier to do this by putting a bit of white paper opposite the focuser so you can really see it against the paper. The secondary should also be "round" indicating it is square to the focuser.
Adjust tilt of secondary so the beam from the laser strikes the primary right in the middle of the centre spot. You may have to go back and forwards with these steps a few times to get it just right but it will improve with repetition. Once the secondary is round and the beam is striking the centre of the primary then....
Adujst tilt of primary so that the beam of the laser is returned back into the laser so it is literally retracing its path showing the mirrors are in alignment.


Now there are better ways to collimate but that will get good views and you will get better at it over time, then it may be time for you to get into the other methods if you choose.

Keep looking up :)

[astro_nutt]

Hi Scott!
How important is the focuser's alignment?..that's a damn good question!!..cause good mechanical alignment from focuser to secondary and secondary to primary delivers the image to your eyepiece. A couple of ways to check this...put a laser collimator into the focuser..turn it on..then adjust the focuser fully in and out at the same time watch the beam on the primary mirror..if it moves across the primary..then the focuser needs adjustment until the beam is stationary...
Cheers!!

[mark3d]

i find collimation is better, faster and easier now that i use a barlow lens with the laser collimator - it compensates for any freeplay in the focuser

http://gmpexpress.net/~tomhole/blaser.pdf

:thumbsup:

[leinad]

Hi Scott, also from learning the collimation process myself with a collimation tool and laser, I found that the laser may have a bit of slop in the focuser when tightened with focuser/eyepiece screws.

So.. collimate to the pri.mirror center spot as well as you can, and adjust primary mirror for final collimation. Then rotating the laser in the focuser around the slop, you'll be rotating a circle with the laser on the primary mirror(looking down the tube opening of course). This will help you know how and where to tighten the focuser screws to roughly have the laser centered in the focuser. Then adjust primary, etc again to get the final beam centered.

Checking with the cheshire/collimation tool after this lets you know how close you are or what final adjustments are needed.

[Entropy]

Thankyou very much for your help guys, this has really helped me a lot.
Im now happy i have a semi-decent collimation, and not only that, but i have a better understanding of the non-optical components of my telescope.

Thanks again
Scott

[programmer]

Hi Scott,

Next clear night try a star collimation test and see how close your collimation is according to that. I'd be interested to compare notes being a beginner myself.

[Entropy]

Sure, no worries.
Today i was really game and actually cleaned my primary and secondary mirrors for the first time. I am very pleased with how well they came up so i have been cleaning eyepieces for the last 30mins or so in expectation of a great night of viewing... and it looks like Mother Nature is going to play nice.

So, hopefully, i will be able to post a nice pic of my collimation attempt tomorrow sometime (Taking the nephew to dreamworld tomorrow, so im not sure what time ill be able to post).

[programmer]

I need to get myself some cleaning fluid for my eyepieces. I gave the primary a wash the other week. It's so tempting to grab a cloth and polish it to death :D but I resisted that urge and followed the method in Astronomy Hacks. I didn't do the secondary. Seems like you'll have some great views tonight.