COLLIMATION - WHAT IT'S ALL ABOUT

[Mr Q]

Frequently this subject comes up on this and other astronomy forums and the understanding of collimation seems to be a deep mystery for most observers.

So here's an in depth tutorial that should answer lots of questions as well as determining if your telescope needs a collimation with a simple star test.

http://w1.411.telia.com/~u41105032/kolli/kolli.html

[Darkstar_1]

Excellent article, well informed and easy to read.

[Macavity]

Good article [iMO]. Does make you wonder (slightly) how many astronomers really achieve the (slightly scary) millimeter limits with the, albeit fine enough (Newtonian / Dobsonian) equipment commonly available.

My own thoughts, albeit re. my ersatz VIDEO imaging of DSOs with a budget 8" / F4 ... Just do the BEST you can? Don't be too discouraged etc. The out of focus star diffraction patterns don't look too great, but the sheer "grunt-power" (resolution) of a fair sized aperture somewhat makes up for this?

Aside: My MAK150 produces far better star diffraction patterns but, on close examination, these look significantly off-centre. And, having invested in an external focusser (to defeat the basic mirror-flop!) I suspect I shall work on that one next.

[Mr Q]

Years ago I was testing my 10" (f4.5) newt's resolving power on the "double-double" in Lyra, which was nearly overhead during (my) steady seeing summer.

The scope's specs (and other sources) said that the scope should resolve down to about 1.2 arc". Doing several tests, I found that the scope could split one of the double components with the Dawe's limit (seperation of the components though merged together) of about 1,5".

Whether a true seperation or Dawe's limit, to me the scope performed well enough for visual observing. I did a star test and could not notice any obvious defects in the difraction ring image so left things as they were. Later, a few re-collimations were needed over the next several years but, for visual observing, the gains were almost not worth the trouble. For astro photos, I would keep the collimation up to snuff, otherwise, a typical collimation problem (determined by a star test) may not be worth pursuing unless you want the most details you can get in photos.

More often than not, bad resolution problems are caused by bad seeing conditions - not a collimation that is only slightly off.

[Northern Soul man]

http://www.astromart.com/articles/article.asp?article_id=548

I used this article to collimate my SCT - really simple if you can digest the info into the grey matter, I've observed with many different types of scopes and have found the poor seeing will degrade the image far more than an "uncollimated" scope will - so long as its near don't worry too much and spend the time observing.

Poor seeing, large temperature differences between day and night, planets low down (Saturn - now), issues with contrast for SCT's, scope not cooled enough. There's a lot against the observer, just have a quick check at a star image - some nights ok, others, a boiling mess. Ive found not to spend a great deal of time on collimating - re centreing - collimating - re centreing (you get the picture) and use the time to observe, the Planets - spend time just looking at a certain planet for a while and your eyes soon start to pick up little "snippets" of surface detail and gradually you can build up your own "impression" of what Astronomy is all about - OBSERVING. Paul.

[PaulB]

I am getting sick and tired of wasting valuable observing time, waiting to collimate my fast F4.8 Orion Optics 10".

So I searched the net and found a very neat little program.

http://sweiller.free.fr/collimation/Collimation03.exe

I collimate my 10" now using. Mire de Collimation, with my QHY5 and PHD. It works very well. And means you can get away with using a star of a fainter magnitude.

For me I can collimate on a 2nd magnitude star, and still make the adjustments in real-time.

However. I am now getting so fed UP of faffing about and wasting valuable imaging time, fine tuning the collimation.

I am thinking of getting a medium-sized triplet apo. In the 4" or 5" class.

Can somebody please invent a mirror cell, that will hold Newtonian collimation

[umadog]

It's not so much the cell that's the problem (at least not a good cell). Usually what moves the most between sessions are the trusses & associated hardware (if present) and the secondary support. It's probably possible to engineer a design that would shift a lot less, but there will be compromises. e.g. thicker spider vanes and heavier mirror cell. With the right tools, most collimation tweaks shouldn't take more than 5 minutes or so. Better to spend the time doing that than to have to cope with a heavy telescope and thick spider vanes.