Collimation update

[GTR]

After deciding last night it's now or never, I think I finally got my Dob Skywatcher mirrors correctly aligned! Does the following I did sound correct?

I began by measuring the spider vanes to check that my secondary mirror was central and it seemed ok. I then made a central pin hole in a cap to fit the eyepiece bit, and noticed one if the three screw bits holding the primary mirror was out of sight on the secondary...basically, the secondary mirror needed tweaking.

I used the weeny Allen key provided and after a few turns here and there on the back if the secondary mirror, I got the entire primary mirror bang on in the middle of the secondary reflection.

I then could see that quite clearly the black circle thing and the tiny circle imprinted on the primary mirror where miles off central!

So with my scope facing a lit wall, I used an Allen key to loosen the three locks behind primary mirror, then I used a screwdriver to loosen and tighten different sides if the mirror til after much trial and error and starting to get a bit cheesed off, I got it pretty much all bang on centre. One downer was that after re tightening the three locks I thought I'd knocked the mirror back out if centre again and it needed a few extra tweaks!! Grr!!

I then had a decent few hours enjoying Jupiter and that bright orange thing nearby which a lady friend at work who's bloke knows astronomy told me is a massive red dwarf. I'm sure the views have improved, infact an out of focus star gave a VERY central looking halo and dark circle in middle! :-) Does all this sound ok? I only used a simple cap, nowt flash!

Oh, one minor issue, my focuser seems to get a touch bit stuck and 'jump' especially when I'm fine tuning into a star or planet. Does the runner it slides up and down on need oiling??

[LukeSkywatcher]

I'm no expert,but what you have done sounds right. Can you post a picture looking down the focuser (with no EP in place).?

The cap you used is about the easiest way to visually see if the mirrors are aligned. I'm not sure i'd oil the stem that the secondary is on. It may allow it to slip or rotate which would cause problems.

[Spec-Chum]

I think he meant to oil the focuser.

[GTR]

Can't do a picture just yet as my scope is kept at my dads house which has much better visibility from his garden! Bit it looks ok to me so hopefully I've sorted it. The three primary mirror clips and of course the mirror itself is all in view and central on the secondary mirror, and the dark inner circle and central point on primary are both central too, possibly a tiny touch out if u look close enough, but for a first effort I'm happy with it! The focuser works ok but fine tuning it can make it 'jump' a bit at times, feels like the focuser tube thing is a touch loose? I CAN focus right and it stays there,, but doesn't feel smooth.

[LukeSkywatcher]

I think he meant to oil the focuser.

Thanks. I see that now. Yes a little drop of oil will help.

[jimmyjamjoejoe]

Is it a rack and pinion or crayford focuser? Either way, check for debris along the runner. Definitely don't oil a crayford, it'l just slip.

If it's a rack and pinion it might be worth removing the tube + gears, cleaning them, and slapping some lithium grease on them. Grease will be better than oil.

It could be dirt, sticky cheap chinese grease, slightly misaligned gear, or all of the above...

[Moonshane]

if it's a crayford (which it probably is), the worst thing you could do is put oil on it. the mechanism will just need tweaking, usually it's the central grub screw on the underside and the two small ones either side of it. it's tricky to describe but easy to do.