Collimation Confusion

[skir]

I've been reading the astro baby guide and I have a couple of questions.

The guide mentions that most collimation issues are down to the primary mirror but then starts out by showing how to adjust the secondary. Should I do step 4 first?

Also do I need a collimation cap and a Cheshire collimator as well?

[Spec-Chum]

No, do it in the order on there.

1. Check spider vanes (only necessary on very first collimation unless you've removed the secondary or unscrewed a vane for some reason)

2. Check secondary is shown as central and circular in the focuser (again, it's very rare for this to have moved unless something drastic has happened)

3. Align the secondary by making all the primary clips visible and the donut on the centre of the primary is in the cross hairs of the Cheshire

4. Align the primary so that the reflected image of the donut overlaps it's own reflection

You only really need to check 3 and do 4 on any 1 night.

Also, I just use a Cheshire for everything.

[Daniel-K]

what scope are you using SKIR?

[skir]

what scope are you using SKIR?

Altair astro 8" f5 Newtonian, which I had delivered a couple of days ago.

[skir]

No, do it in the order on there.

1. Check spider vanes (only necessary on very first collimation unless you've removed the secondary or unscrewed a vane for some reason)

2. Check secondary is shown as central and circular in the focuser (again, it's very rare for this to have moved unless something drastic has happened)

3. Align the secondary by making all the primary clips visible and the donut on the centre of the primary is in the cross hairs of the Cheshire

4. Align the primary so that the reflected image of the donut overlaps it's own reflection

You only really need to check 3 and do 4 on any 1 night.

Also, I just use a Cheshire for everything.

Thanks for that. Can you just use a collimation cap for everything or is that not possible?

[skir]

Also, there seems to be about a mm to a mm and a half difference in the length of the vanes. I guess I will need to re-adjust these?

[rwilkey]

I don't check collimation on every trip out, I only check occasionally. If you have a new scope it should not be out by much, but always good to double-check. Just get a Cheshire collimation eyepiece, you don't need a collimation cap as well.

[Spec-Chum]

Thanks for that. Can you just use a collimation cap for everything or is that not possible?

Not really, you need the cross hairs to align the secondary.

Also, there seems to be about a mm to a mm and a half difference in the length of the vanes. I guess I will need to re-adjust these?

Nah, one of mine is about 2mm shorter and I've never got around to fixing it...

[Moonshane]

first thing to do with collimation of a new scope in my opinion is check things before you adjust anything other than the primary. you may find that the collimation is OK bar a minor tweak on the primary so in that case (as with most cases when you check the collimation) it's a very quick and easy adjustment.

it's better to get them as close to central as you can assuming the tube is perfectly round - none of mine are so I just do my best. not something to overly worry about as you can adjust this and any leaning of the focuser out by the secondary tilt with no visible detriment.

broadly if the vanes look pretty central and the secondary looks pretty round and central in the focuser drawtube then this is OK.

you then need to get the secondary and then the primary aligned with the cheshire as described above and in AB's guide.

don't agonise over it though as the primary has the biggest effect by far and is easiest to adjust, the secondary has less effect and is tricky to adjust.

[skir]

I should of said this in my first post really. The scope is second hand so it will have been collimated previously I'm sure. But it has been couriered to me so could have been knocked out a bit during transportation I guess?

[skir]

Sadly I did not get a user manual with the scope. So another question. Behind the primary there are six large plastic knobs, 3 are black and 3 white. The black ones have a spring each, the white ones are just threaded bolts. Are the block knobs for colilimation?

[Peter Drew]

Yes, the black ones are for collimation and the white for locking. Recheck your collimation after using the locking screws.

[skir]

Ok, first step then is to get a collimator, I've got one on order from FLO.

In terms of adjusting the position of the primary. Do you loosen all of the knobs on the back, do the adjustment and then tighten the collimation knobs followed by the other knobs?

The seller tells me he collimated the scope before it was delivered, but of course it could have been knocked out in transit.

[Moonshane]

the collimation can be knocked out ever so slighty when lifting the scope from the house (after collimating) onto a mount. I always collimate in situ once cool and set up. it's part of owning a newt albeit a small part once you get the hang of it.

personally I don't like locking bolts and usually remove them. if the springs are half decent they should retain position in use. as hinted at by Peter, they can affect the collimation when tightened if not careful.

[skir]

So would it be worth only using the locking bolts when the scope is being transported?

[Moonshane]

possibly so thinking about it. if I were making a mirror cell, locking bolts would not feature.

[skir]

Well I think I need to get a collimator on it and see if it does need doing first and then go from there.

[Moonshane]

definitely the right thinking. many people start fiddling and realise it was not that far off in the first place.

[skir]

Well I've received my Cheshire collimator in super quick time from FLO and got the scope all setup and ready to go. It did require some work, but I guess that is to be expected after its been couriered.

thanks for everyone advice on here