RE: [ATM] 25" mirror possibilities

[Ken Hunter <atm_ken_hunter@yahoo.com>]

Another option...

Until proven otherwise it's just a glass blank with
the possibilities of future use in a telescope.

The option is to trade it for a blank that is known to
"fit the bill" ie. is the right shape, size and figure
to make the telescope that you want. For instance, if
you want a 20 inch F5 parabolic mirror to put into a
scope, trade it for that.

The person trading would have to then figure out what
to do with it or perhaps they are looking for a "piece
of glass" that size.

Ken Hunter


--- Scott Milligan <starzkey@charter.net> wrote:

> 
> 
>   I recently obtained a large (25" full thickness)
> mirror on Ebay.
> (Aperture fever struck.)  This is a unique piece,
> and I would really
> appreciate some ideas from other atm'ers as to the
> best way to put it to
> use.  
> 
>   
> 
> Dennis:
> 
> Short of reconstructing the Wright-Schmidt corrector
> plate and using as is
> (a time consuming and/or expensive proposition), I
> suggest one of two
> possible uses for large, thick glass:
> 
> 1: Make into a flat, and use the flat to test other
> optics.  Unfortunately,
> this option doesn't make much sense if all you want
> is one, large telescope.
> 
> 2. Pay someone to lightweight the substrate by
> generating a conical profile
> on the back and coring a hole through the center. 
> Then, refigure the
> optical surface into whatever kind of 'scope you are
> looking for, and use
> the perforation in a center mount concept.
> 
> A full thickness blank can be an asset to an optical
> shop, since the
> thickness will help minimize self-weight deflection
> when mounted in the test
> stand: therefore, full thickness blanks of moderate
> aperture make excellent
> flats when used in a temperature stabilized
> environment.
> 
> The extra thermal mass, however, is a drawback when
> used in a telescope,
> since it will take MUCH longer to come to thermal
> equilibrium as the ambient
> temperature drops around it.  The result; a
> turbulent layer of air near the
> mirror surface is always present, preventing the
> 'scope from attaining it's
> theoretical resolution and contrast transfer.  Of
> course, this problem could
> perhaps be adequately managed by installing the
> scope in a permanent
> observatory, with some degree of temperature control
> inside the building.
> 
> A third option is to ignore all of the above, wing
> it, and put it into a
> telescope.  But my recommendation would be to not
> spend a lot of money doing
> that, until I had discovered whether or not the
> thermal lag problem is
> significant.
> 
> Scott Milligan
> 
> 
> 
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> ATM mailing list http://www.atmlist.net/
> 


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