Collimation of a 200p (no laser)

[Avocette]

I have read up many of the threads here about collimation (many thanks to astro-baby etc) and set about my first attempt armed with a collimating cap, home-made from a 35mm film canister, to supplement the Skywatcher Cheshire collimating eyepiece which I bought with the scope.

I adjusted the secondary Allen screws until I could see the three mirror clips equally visibly from the collimating cap. Then I inserted the collimating eyepiece and looked at the primary mirror centre spot ring and adjusted to align it with the cross hairs of the collimating eyepiece. I got things aligned and had a satisfactory session viewing the moon and saturn with a couple of its moons showing well.

However later I was trying to figure out why the two sets of cross hairs and the centre spot ring were not all aligned if collimation was correct. Looking through the collimating eyepiece there are two sets of cross hairs, the local ones that for me are rather difficult to focus on, and the much clearer image of them as seen after reflection by the secondary, primary and secondary mirror again.

The local fuzzy cross hairs did not line up with the reflected image of them but were rather to one side.

So this morning I've started again, and this time set up the secondary so that in addition to being able to see the mirror clips evenly via the collimating cap, a fine subsequent adjustment lines up the fuzzy cross hairs with the centre spot ring. Then the primary mirror adjustment brings the image of the cross hairs into alignment with the fuzzy real ones and the centre spot ring.

I feel as if this makes sense now - it is surprising that there are no instructions supplied with the collimating eyepiece!

By the way I'm quite happy with the physical fit of my home made collimating cap and the Skywatcher collimating eyepiece which are both fairly snug in the focus tube without tightening the knurled screws.

I also noticed that the adjustment of the primary mirror involves compressing the three neoprene O rings through which the adjustment bolts pass. I guess these may eventually lose their elasticity?

[triton1]

I to have a 200p but have springs instead of washers.Has your;s been modified.I use a laser with cap and find i have to redo every time i use it.Also collimation changes when the scope cools down.

regards Jonn

[nightfisher]

Avocette, good post, im just starting down the collimation road, having always used refractors, your post makes sense

[NGC 1502]

From post #1 -- "I guess these may eventually lose their elasticity" ?

The 3 neoprene washers can be replaced with these http://www.classic-bike-shop.com/70-1574-thackeray-washer-385-p.asp

Known as 'Thackeray washers' or double coiled spring washers.

Some good DIY shops stock them, or online.

Regards, Ed.

[Scott]

Avocette, good post, im just starting down the collimation road, having always used refractors, your post makes sense

wow Jules, 7079 posts without owning a reflector . made me laugh.