Perfect collimation

[The Warthog]

I had been messing about with the collimation on my Newt for a little while, and I seemed to have lost all my collimating powers. I would have done a simple collimation, primary only, but I had noticed that my secondary was too far down the tube, probably as a result of messing with it over the last couple of years, and cranked all the screws back and then started trying to point the secondary at the primary again.

It seemed that every time I started to spend some time on it, SWMBO would interrupt with something in the house that needed fixing, and the last time I tried, I gave up in frustration.

I was all set to do it this afternoon, then my son asked me to make a filter for his pond, which used up an hour and a half, but with that out of the way I went into the house to get the scope. Into the kitchen and my wife is on her knees with the bottom drawer apart, but I was on a mission. I got her a drill and bits, and took the scope and my allen keys out to the patio table.

I had read Astro Babe's excellent primer on collimation, and noted the key phrase about making little adjustments to the secondary. I put in my Cheshire, and soon found that I wasn't nearly as much off as I thought. Two or three minutes sufficed to get the secondary sorted (put the centre spot in the crosshairs, and the mirror clips will be in the right postition,) and it took about 15 minutes to adjust the primary and line up everything, while explaning to my son what I was doing.

Of course, it's too cloudy to do a star test, but I'm not worried that it will be off - the view through the Cheshire was perfect.

I think the difference between today and the previous attempts was mostly attitude. I have paid little attention to he secondary in previous collimations, except to make little tweaks. Moving it up the tube was a new beast to me. Adjusting the primary is pretty much second nature to me now, although somehow it made more sense today. That may be a result of reading Astro Babe's primer, or it may be, too, that my brain was firing on all cylinders today.

Anyway, to learn from my experience, if it gets frustrating and annoying, walk away for a while. Clear all other distractions away, sit in a nice chair in the sun, and take your time. It will all work out in the end.

[philsail1]

That's inspiring stuff "Warthog!" Glad you got your collimation sorted.

One question - "How does one know when the secondary mirror is in exactly the correct position with regards to distance from main mirror?"

Regards,

Philsail1

P.S. I'm up at this hour (04.21 in UK) because of bad backache after building garden wall yesterday!

[The Warthog]

That's explained very well in Astro Babe's primer. Basically, you eyeball whether it is exactly central in the focuser tube, or is too close to the front or back edge. It was quite easy to see that my secondary was too far down the tube.

[philsail1]

Thanks for quick reply there "Warthog," I'll look up "Astrobaby's" primer (later this morning, as I'm off back up to bed!).

Thanks again,

phlsail1

[Beulah]

I totally agree with the attitude aspect. Most collimation only needs tweaking - and a lot of patience. It really cannot be done when the "Honey Do" jobs are pending.

I was extremely fortunate that one of the best and FIRST pieces of advice I found whilst Googling was not to collimate with the tube in a vertical position

Astro-Baby's article is excellent, I don't think I have read one in such detail, especially regarding the spider alignment. It's people like these that make learning this malarky all the more speedier and accessible.

[Astro_Baby]

Thanks guys - I only wrote the article cos I was frustrated when I had to relearn it all. Plus last year there was so much cloud I thought I'd put my spare time to some use that (hopefully) benefits other astro folk.

Tha patience thing is something I do stress in the guide - its a job that needs your complete attention and a decent time budget. If you get it done in 15 minutes when you'd budgeted for 4 hours thats super and you now have 3hours and 45 minutes to watch the telly, have a beer whatever. If it takes 4 hours and you budgeted for 15 minutes then stress sets in, relationships suffer and telescopes can start flying around the room

Glad the guide is being of use to other astro folk though.

[centroid]

There's no doubt that trying to achieve "perfect" collimation can be a a frustrating task.

With 'Newts', one can make use of things like Cheshire eyepieces, to aid the task. I discount Laser Collimators, because these themselves, need calibrating, if they are to be of any use. I know that many people have tried them, then given up, and gone back to the more reliable/traditional approach..

For SCTs, there really is only one way, and that is using the Mk.1 eyeball and a star.

Hotech have introduced a Laser Collimator, that employs rubber compression rings ('O' rings), to centre the collimator in the eyepiece adapter of the scope. However, they then go on to say, that first the scope must be collimated using a star, and the Laser Collimator, calibrated against the collimated scope.

I suppose if you frequently need to re-collimate your scope, then perhaps the Hotech unit, would provide a quick reference for checking to see if the collimation has shifted. Other than that, I can't see that it would serve any purpose.

The main problem we face in trying to see a set of Airy rings, is the 'seeing'.

With an SCT, seeing the and centreing the dark ring of the central obstruction, within the light circle of the defocused star, is pretty easy.

However, seeing the Airy rings for the fine tuning, is very much affected by the 'seeing', and these a easily lost in the twinkling image.

An artificial star offers a good alternative, but then, as in my case, with a focal length of over 3 metres, the distance from the scope, that the artificial star needs to placed, is not that practical.

There are some software package that can be used, such as Metaguide and CCD Inspector.

Metaguide is a 'freebie', and I have tried it for collimating, but was not too impressed.

CCD Inspector is an advanced piece of software, but at $179, a very expensive option indeed. Plus the fact, I have read some negative reports on the various forums.

Having said that, I tried the 'demo' version, and thought it was quite good. But not $179 worth of good.

BTW,

Into the kitchen and my wife is on her knees with the bottom drawer apart, but I was on a mission. I got her a drill and bits, and took the scope and my allen keys out to the patio table.

Nice one WH!!

Dave

[Doc]

but I was on a mission. I got her a drill and bits, and took the scope and my allen keys out to the patio table.

This made me laugh. If this was my missus the drawer would still be on the flloor until I fixed it.

This made a very interesting read WH. AB's primer is very good indeed and very easy to follow.

[The Warthog]

Also, I gave the tube a wash with a damp cloth and dish detergent. I was able to remove some paint transfer, dirt and stains that had gotten onto it, and made it look almost like new again. I'm sure that will contribute to an improved optical performance, as noone can be at their best when they're looking a bit drab.

[albedo0.39]

Sort of pleasing that someone as experienced as you still gets the tweaking bug and also somewhat worrying that collimation is such a difficult subject to achieve satisfaction on - despite being (in the textbook) "easy"...

I've got all this to come, I'm sure (sigh)