Why collimate?

[JonnyP]

I'm guessing that this is a completely ridiculous question, but here we go....

I assembled my SW 200 dob a few days ago and while it was cloudy I thought I'd check out the instructions for collimation. The secondary mirror is correctly aligned, but the primary mirror is slightly out. I didn't want to play around too much for fear of snapping a bolt, or worse, breaking a mirror. (Can't break my new toy too soon so I'll wait to get some local advice.)

I took the telescope out a couple of night ago and got some nice views of Albireo, Jupiter, M103 and the moon.

Compared to my last cheap telescope, the images looked pinpoint sharp in the ep with a lot more background stars, so I was wondering how much difference a completely accurately collimated telescope would make.

If it was 100% in collimation, would my newbie eyes be able to see a difference? As I get more experience will collimation become more important? Is an experienced astronomer able to look through a scope and say 'this telescope is out of collimation.'

Or have I got entirely the wrong idea about collimation, and it means something completely different?

[John]

If a scope is not in reasonably good collimation it simply can't perform at it's best in terms of resolution and contrast. So you either won't see, or won't see as clearly, the finer details of astronomical objects.

[x6gas]

If you are happy with the view then there is no need to rush to collimate your 'scope IMHO.

Rather than checking for alignment of the mirrors, have you tried a star test? Focus on a reasonably bright star and then de-focus slightly either side and check what you see. If the 'scope is perfectly collimated you should see a nice Airy pattern of concentric circles. If the Airy pattern is skewed off in one direction then your scope needs collimating. At some point it is worth learning how to collimate your scope. Astro Baby's guide is great...

Poor collimation on my scope really shows up on my astrophotography and I think you'd notice it on bright objects like Jupiter. At the end of the day, if your scope isn't properly collimated you are not getting the most out of the instrument, but at the same time if you are happy with the view then I wouldn't stress about it!

[JonnyP]

Rather than checking for alignment of the mirrors, have you tried a star test? Focus on a reasonably bright star and then de-focus slightly either side and check what you see. If the 'scope is perfectly collimated you should see a nice Airy pattern of concentric circles. If the Airy pattern is skewed off in one direction then your scope needs collimating......... but at the same time if you are happy with the view then I wouldn't stress about it!

I tried a star test the other night, and sure enough the Airy pattern is slightly off centre - not massively so.

As I thought, if I can live with it for a few weeks, I'll be ok!

(Mind you I used to say that about tuning a guitar and never got into a band....)

[faulksy]

I tried a star test the other night, and sure enough the Airy pattern is slightly off centre - not massively so.

As I thought, if I can live with it for a few weeks, I'll be ok!

(Mind you I used to say that about tuning a guitar and never got into a band....)

[x6gas]

Nothing quite like the satisfaction of seeing a perfect Airy pattern though!

When you do come to collimate, check that your spider vanes are correct. I was surprised that mine were quite a way off 'out of the box'.

[swamp thing]

Nothing quite like the satisfaction of seeing a perfect Airy pattern though!

Oh I dunno! I think I'll settle for the horse head nebula rather than an airy pattern.

Just kidding I know what you mean.

Regards Steve

[Moonshane]

your guitar analogy s perfect. learn to collimate. it will ensure you get the best from your scope. it's an easy process once you learn it.

[umadog]

When you star test you need to make sure that the star is exactly in the middle of the field or the airy disk will look asymmetric.

This thread explains what you're doing when you collimate: Telescope Reviews: Concise thread about autocollimators+improvements

The axial alignment is the critical thing. You want to have the whole field of view in focus at the same time. If this isn't right then your images will be slightly blurry. Faster scopes have more critical tolerances.

[todd8137]

i never touched my 300p for a year when i did get round to have in ago,it was miles out ,the secondary and main were crazy ,now at the time i still could see every thing with out a problem ,but once don things just seemed that little bit brighter

[JonnyP]

i never touched my 300p for a year when i did get round to have in ago,it was miles out ,the secondary and main were crazy ,now at the time i still could see every thing with out a problem ,but once don things just seemed that little bit brighter

That's interesting and is probably what I was trying to establish ie would my newbie, inexperienced eyes be the limit in the detail I could pick out, or would it be collimation that is the limit. (Or for that matter, LP or seeing conditions..)

Thanks for all the replies guys. I will certainly learn how to collimate over the next few weeks.

[John]

In a way you could say that you won't notice until you read others with similar equipment reporting seeing details that you are constantly struggling to see with your scope, eg: fine details on Jupiter, Saturn's Cassini Division cleanly defined, details on Mars, etc. Often of course it's the seeing conditions that get in the way of seeing these more subtle details but when things come good, thats when you want your optics to be "on song".