Re: [ATM] which Collimination tools?

[Bruce MacDonald <brumac@gmail.com>]

Hmm,
I think that that is ALWAYS sound advice.

My experience:
I started out using the good ol' film cannister, and lined everything
up "by eye".  It worked and the views were good.

Then, I bought a cheshire collimator (to be technically correct, a
combo sight-tube/cheshire) from a friend, and discovered that what
looked symmetrical and "OK" using the film cannister could be improved
with the cheshire.

I then bought a 10" f/5 dob in need of rehab.  I could not put the
peephole of the cheshire in the focal plane 'cuz it would not rack in
far enough to accommodate the 45° reflective part of the cheshire. 
Consequently, I could not see the full diameter of the primary
reflected in the secondary.

I bought a set of Tectron tools, which included separate sight tube
and cheshire and an autocollimator, with which I had previously had no
experience.

The sight tube instantly revealed that my focuser was not square to
the main tube.
On re-checking the defect was indeed visible using my old cheshire,
but not "obvious" as it was using the sight-tube.  After aligning the
primary using the cheshire, I tried the autocollimator.

The autocollimator goes dark when the scope is correctly collimated,
but even within the dark range, you can see ghost images of the
primary mirror's centre spot.  The merest tweak of only one of the
primary collimation screws eliminated that.

I've only ever played around w/ a laser collimator.  I found it
frustrating.  Also, how do I know that the laser collimator is itself
collimated?  People that own 'em love 'em.  Who am I to argue?

So, my recommendations:
What you need depends on how accurate you want to be.  
I prefer the separate sight-tube/cheshire to the combo -- it just made
the job easier.

I found the views dramatically better after squaring the focuser.  I
could not visually see the difference using the autocollimator.

Since I've only done this excersise start-to-finish on an f/5, this
probably has affected my opinion.  I understand that with very fast
scope, even the slight tweaks make a big difference.

--BM





On 7/24/05, John Moore <jamoore42@yahoo.com> wrote:
> Hi All,,
> 
> Thnx to all who replyed,, sounds like they are tools that are nice to have,,
> but not mandatory,,  I'LL let my budget decide.
> 
> thnx for the help!!
> 
> John Moore.
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