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Collimation virgin (soon to be ex)


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Hi guys,

Got my long cheshire this morning, from that well known auction site, was second hand and looks like it was originally from joy's optics on the same site.

Have followed the astro baby guide, but before I start messing with it, wanted to double check a few things; (working on the principle if it ain't broke, don't fix it)

1. There is a lot of slop when it's in the focuser, so much so that the dots and crosshairs can be lined up, or quite a way off depending which way I move it. If I tighten the lower screw first then the second, it appears to be fairly close, I guess if I do the same order with the eyepieces it should be ok.

Or, should I put some tape on the cheshire to make it fit, as I have seen suggested on here? But wouldn't I have to do the same on the eyepieces, so not keen.

2. I measured the spiders to check the secondary is centred, and it's 1mm adrift on one axis, do you consider that close enough?

3. Checking the secondary is centred in the focuser, again the slop makes a difference, as does moving my eye across the hole.

4. I can't see the mirror clips in this cheshire so will drill a cap assuming I have a small enough drill bit?

I was expecting a bit of slop as I've noticed it on the eyepiece, but didn't realise it makes such a difference to whether things are lined up or not.

It looks like the secondary needs moving up the tube a little, but everything else ok? Have attached the view below, any advice would be most welcome.

Was hoping to get across to sgl9 but sadly too much to do today.

Many thanks in advance

Mark

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the secondary needs to go up the tube as you say, use your cheshire for this, simply put your cheshire in your focuserand move it in towards the secondary, untill all you can see is a small margin/border around the mirror then adjust accordingly

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Thanks guys,

Will probably have a crack at it next weekend, I'm reasonably comfortable with the theory so should be ok.

My main query was to do with the movement of the cheshire in the focuser, is such slop normal?

I've read it's a major issue with lasers, but didn't think it was a problem with cheshires?

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Hey, I took the plunge and had a go last night. Drilled a hole in the focuser dust cover to make a collimation cap.

Got the Spider within a fraction of a mil.

Got the secondary centred in the focuser but then couldn't get the primary mirror clips straight without moving back down the tube a little.

The three Allen bolts didn't have as big as movement impact as I expected, so had to move it on the centre screw.

Primary was a little adrift but got the dots to match up using the cheshire, although crosshairs still a little off the dot.

All in all, not as much to worry about as I first thought. At least I didn't make it any worse and having had a quick look at the moon an hour ago, I think it's an improvement on where it was, but then clouds moved in so no chance to do a star test yet, maybe later.

The second time will be easier and I hope I can get it closer, will have another crack when I have a couple of spare hours.

One question though, the dots match up, but the cross hairs of the cheshire not on the dots, is that a secondary issue?

Ta

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