Disasterous 1st Collimation

[ramstar]

Wish I'd never touched it! Thought I'd read all the various videos etc and understood what was required - obviously not! The side clips have disappeared (checked down the sofa but not there - don't know where else to look).

I am totally confused, frustrated and not sure where to turn to next? I've been using a Cheshire but the images I've seen don't really correspond with the photos & videos I've seen. The secondary has sometimes looked elliptic rather than circular! I'm now so unsure as to what to do next - is there somwhere I could take my scope to to put me back on track?

[Dude_with_the_tube]

collimation is quite a straight forward thing to do,but obviously something terribly wrong has happened with your first attempt.sorry to hear that fella.You will be better off checking the net where is the nearest astro club in your area or if there is none,then astro shop like FLO,Rother Valley optics etc and bring your scope down to them and let them have a look at it. i hope you get it sorted.

[rory]

second the astro club idea. see if theres one local and pop along . what scope have you got ramstar ?

[ramstar]

It's a Skywatcher 200 Dob. Trying to follow some instructions from Astronomy shed - see how I get on

[brantuk]

Get the secondary mirror looking circular for a start - you may have twisted it out of position. Then rack the focuser tube in and out slowly till the primary three mirror clips appear round the edge when looking stright down the center of the focuser tube. I'm not familiar with the Cheshire collimator so someone else will take over from there.

[Peter Drew]

As Brantuk says, it's essential to get the secondary correctly positioned first otherwise you end up correcting an error on top of another error. The further in you rack your focuser the more of your primary mirror you will see reflected in the secondary mirror. If necessary, rotate the secondary mirror until it looks circular and the image of the primary is central. If at that point the three mirror clips are not equally visible, the primary mirror should be adjusted until they are. This is much easier if there is someone else helping by turning adjusters whilst you look in to watch the results.

[bingevader]

Sometimes you can't see the mirror clips through a cheshire, I know I can't through mine.

It is possible to centre the primary without seeing the clips.

It is easier when you can see them however, so I use an old 35mm film canister with the bottom cut off and a tiny hole dead centre of the lid.

Start with the secondary and get it looking circular first.

Cheers

[ramstar]

Maybe I'm getting somewhere at last. Looking down the focuser through the Cheshire, I now have a circle with the inner ring more or less central. To make it easier to view everything I have blocked seeing the primary with a sheet of paper placed just below yhe secondary - hope I'm ok to here? Now removed the paper and can see 2 clips, though the whole thing appears to be off centre!

[Astro_Baby]

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

have a read of that if you havent already.....

[Matt Scunthorpe]

I have the 200p Explorer, and i cannot see the clips through a cheshire when i collimate mine. I dont know if this is causing extra problems, but like bingevader said, it can be done.

[umadog]

If you're really confused then it's best to just find your nearest club and ask them. It's easier to be shown in person. A lot of the guides don't explain why you're doing things, they just tell you what to do. If you have a problem not covered by the guide, then you're not able to fix it because you don't know why you're doing a particular step. The mirror clips is a great example: if your secondary is too small then you'll never be able to see all the clips at the same time. The guides mostly don't say that.

Here's a collection of the better links and a description of what the whole procedure is for: http://www.physiol.ox.ac.uk/~raac/collimationLinks.shtml

[Matt Scunthorpe]

I would definately double that advice above on going to a local club and getting it done properly, and shown how to do it. Thats how i first learnt the technique.

[ramstar]

Thanks all for your advice - I realised that I would continue to struggle the way things were going so have contacted a local society and a kind member has agreed to help me next week. With a brief gap in the clouds tonight at least I'm still able to see Jupiter (though not very clearly) so maybe all isn't lost!