Re: [ATM] first light on a Lurie-Houghton

[Alexis Cousein <al@sgi.com>]

David Weinshenker wrote:
> finicky
> enough (according to the figures given here) that it
> needs a "test and adjust" process to go from the
> initial "installed by measurement" alignment to the
> optically optimum setting (as does the primary mirror
> of a fast reflector).

The same holds for SNs: you do indeed need a *collimation
procedure* for a scope like that, not something you can
measure once and for all and forget.

You don't necessarily need an adjustable corrector for the
*main* error: the primary is spherical so it's got
many possible "optical axes". If you adjust its tilt,
you can get rid of coma (at the expense of very mild
astigmatism, unless your mechanical alignment is way off).

But if you want things perfect (including illumination and lack
of any astigmatism on-axis), then yes, you need to be able to
shim the corrector.

If it's at all like what you have on an SN, you should be able to use
a a sight tube's cross hairs' faint ghost reflection on the corrector
to see whether your collimated combined focuser/"optical" axis after a
Newton-like collimation hits the corrector squarely.

-- 
Alexis Cousein                                  al@sgi.com
Senior Systems Engineer/Solutions Architect     SGI/Silicon Graphics
--
<If I have seen further, it is by standing on reference manuals>

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