Bob
):-{])) <---- madden@netcom.com madden@svpal.org Remember amateur astronomers: "keep looking for the next Universe"
On Thu, 20 Apr 1995 harrington@genie.geis.com wrote:
> To: grant@aretha.llnl.gov (Chuck Grant)
> Subject: Mirror cells
>
> Chuck,
>
> >The rubber mat technique fails for the same reason, slight
> >irregularties in the mirror, mounting plate, mat, or heat distribution
> >cause uneven compression of the mat. Using a rubber mat is better
> >than just leaning the mirror against a "flat" plate, but not nearly as
> >good as a flotation cell. A technique like this that relies on
> >compression needs a lot of compression to have an even distribution of
> >force, but this causes widely different compressions (and thus focus
> >shifts and unevenness) with different tilts.
>
> You're right, of course, but I found that at least the gasket material
> (keep in mind, this is not just convention rubber mat) worked just fine
> in my 13". Perhaps it was just dumb luck. To overcome what you
> described as uneveness at different angles, I found it necessary to add
> three 1"wide x 2"long x 1/4"thick pieces of aluminum along the bottom of
> the mirror mount. Also lined with felt, these prevented the mirror from
> shifting in the L brackets when tilted near the horizon. (Because of
> the mirror's lighter weight, these were unnecessary when I made a
> similar mount for an 8".)
>
> Cheers,
> Phil Harrington
>
>