Re: [ATM] Mirror alignment?

["David Harbour" <scarab2@cox.net>]

Geo,

It is instructive to remember that most of the truly "Great Telescopes", the
ones with which pivotal, foundation discoveries in cosmology were made, were
not collimated with lasers. The Hale 5 metre, the Shane 120", the Hooker
100"- I remember discussing this subject years ago on the list. I can
usually collimate a large, fast Newtonian in about two minutes; my record
was about 30 seconds. I may perhaps have a previous post that describes my
method in detail; it was commonly practiced for decades, and did not use
either a Cheshire eyepiece or lasers. If I can't find this post, I'd be
happy to re-write it; but just to get you started, before you ever look at
the position or angle of the secondary, you must make sure that the primary
is SQUARED ON. Make sure the secondary holder is PRECISELY CENTERED ON THE
OPTICAL AXIS, NOT OFFSET. Sqauring on the mirror and verifying that the secondary 
holder is on optical axis can be done simultaneously in one operation. About offset secondaries: 
Offsetting the secondary is (in my humble opinion) a fad of dubious value, and did not come into vogue until the last half
of the century,  and will COMPLICATE collimation. An f/8 system does not
need an offset secondary. No Newtonian requires an offset seconday; their
only advantage is to provide a circle of vignetting free illumination that
is centered on the optical axis- big deal; everyone deals with some
vignetting- what difference does it make if it is not quite even throughout
the field of view? To me it is just another fad (sorry- don't mean to step
on any toes of atms who think it is imortant; all my scopes performed
flawlessly without offset secondaries and were much easier to collimate).
Write to me off list, and I will compose the "longish", comprehensive method
for you, if you would like.

David Antoninvs Harbovr
scarab2@cox.net
http://www.atmsite.org/contrib/Harbour/index.html
http://www.atmsite.org/contrib/Harbour/Foucault.html


----- Original Message ----- 
From: "Tax Payer" <taxpayer779@hotmail.com>
To: <atm@atmlist.net>
Sent: Monday, April 18, 2005 8:02 AM
Subject: [ATM] Mirror alignment?


> Hi folks,
>
> I just received a mirror from a fellow ATM'r and have installed it, but
> having a heck of a time getting it properly aligned.  It's a 4.5 f8.  I
> don't have any equipment like lasers and such to do testing.  Can anyone
> suggest the best way to do this, or forward a URL or two with a site that
> describes the best methods?  Thanks in advance.
>
> Geo
>
>
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