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Collimation


RayGil
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Hello Group.

Info:

I have been active in astronomy and owned different scopes for over 10 years now, although it's only in the last year that I have been active from a reporting/discussing point of view, astronomy was always my second hobby, being a Radio Ham was my first.

Times have changed and astronomy has now taken over from radio.

Over the last few months I have seen many posts about collimation from people either having new scopes or buying second hand scopes.

My question is, When to actually collimate?

In my 10 years I have never had to do this? Ever! yet I see posts from people that collimate their scopes as a matter of course, every couple of months?

The reason I pose this question is, recently I bought a SkyWatcher 200p and along with the bundle that came with the scope was a LaserDream Deluxe laser collimator from Astro Engineering.

So do Larger Newtonian scope need collimation more often? I use my scope at a dark sky site, which I have to travel to, so I would say I may need to learn how to collimate at some point.

My other question is are people just collimating their scopes way to often or is it just a fact of life that larger scopes need more adjustment?

My understanding is this, I fix the laser into the eyepiece tube, switch the laser on, rotate the collimator and observe the laser dot, if it stays in same position while you rotate it, it's fine!

If it produces a small doughnut, or small orbit then the scope needs adjustment?

Have I got that right?

Ray

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Hmm, the collimation 'can of worms'!

Some swear by collimating several times a night, some do it every session, some less so.

I find if you are careful with your scopes then collimation is not required all that often. My 6" travelled down from Lincs with me nearly 3 years ago in the car, has had regular use and kept it collimation spot on. I went to Luckshall with it in March and on return it needed a tiny tweak to get it back to spot on (and I mean, tiny!)

The SW200 was way out of collimation when I brought it back from Kent in the car, so was given the laser treatment. Since then, I have used it nearly every clear night and it is still holding collimation perfectly.

When you get into the realms of 14" + I think you need to collimate fairly regularly, but, with careful handling, you can get that down to every now and then.

I think that sometimes, too much fuss is made of collimating. If you're purely visual, you can get away with letting it slide a bit before it infringes on your viewing pleasure. Imaging is a bit less forgiving though.

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The bigger the scope, or the faster the scope, or if it's a truss tube scope then it needs collimating frequently.

I have to do mine everytime I use it, but after a while it's dead simple.

Your question about turning the collimator in the focuser to see if the dot moves really only applies to see if the collimator itself is collimated.

The red dot will tell you if your mirrors are aligned. If the red dot missed your primary mirror donut then the secondary will need adjusting and if your return beam misses the required hole in the collimator then your primary needs adjusting.

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Because it's a 16" truss tube dob. Everytime it's striped down the truss tubes are removed, OK I've marked them but they are exactly in the same place. Just moving it around can cause the mirrors to wander slightly, it's only a quick 1/8th of a turn but I'm a bit picky and hate comet tailed stars so have learnt to do it everytime, it takes seconds thats all.

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Just to update, I watched that video on YouTube, it uses the same laser that was supplied with my scope, so I built up the scope and checked, primary slightly out, adjusted and secondary blob on! so really easy to do, and I will keep a check on it now, I guess with moving the scope all the time to the dark sky site, things tend to move.

Cheer's

Ray

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I collimate my 6" and 12" dobs every time I use them. I carry them out and back in after and before each use so they mirror is bound to shift slightly. As Mick says, it's just a little tweak here and there once you get it close the first time you do it properly.

The problem with larger mirrors is that the mirror shifts about slightly when you move the scope around and this inevitably affects the collimation, and in faster scopes (eg f5) this can make a big difference. For visual use as Hugh says, it's not as critical as imaging BUT I can see the difference in contrast and colour (on eg Alberio) between the scope when collimated with the Cheshire/Laser (I use both from time to time but have found the Cheshire easier in daylight - laser in darkness) and when tweaked slightly during the star test done after collimation is 'spot on' with the usual tools.

bear in mind it's 'impossible' to get, and during the average session keep, collimation 'perfect' so just get it as close as you can and do it as often as your scope tells you is required.

good luck!

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Thanks Astro-Baby, I have also read your guide, which is very good, My next option is to do a star test I think.

But with a well looked after scope, and mine is, the offset should be, when moving the scope in and out of the house and transporting it to the dark sky site. I will keep a check on it, but the simple laser collimator should suffice for now, before I go to the expense buying the extra's.

Cheer's all

Ray

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i collimate before every session, its second nature now... i travel to and from each session by car and the tracks that lead to my obs site are bumpy. The collimation has been slightly out each time, the only time i didnt collimate (when i forgot my hotech) the viewing was pants, contrast bad, stars not becoming pin sharp etc...

I think a lot of people are scared to collimate because it means undoing screws and bolts, i felt the same when i first got my 12" but given the choice between mediocre viewing and letting the scope show its true potential then im glad i collimate prior to each and every session, it only takes me about 30 seconds now

Edited by Llamanaut
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Once the donut,primary and secondary all look pretty centred and you can see all 3 clips on the primary...............you are good to go.

Now concludes the idiots guide to collimation.................(me being the idiot).

ha ha

I'm sure you're not mate. the good news is that your scope having a reasonably small mirror will hold its collimation for long periods. :D

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All sorted with collimating now, I will put the laser in my kit bag and just keep checking it when I've set the scope up, there does seem to be an awful lot of confusing info out there!

I'm glad I have SGL for advice!

Cheer's and thanks to everyone who commented.

Ray

Cumbrian Skies

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