Re: [ATM] Optical flat part II

[Jarvis Krumbein <jkoptic@juno.com>]

Vladimir, the liquid flat is a very old idea.  Back in the early 50s we
had a test stand which used a pool of mercury as the reflective surface. 
A thin film of mineral oil kept the fumes from the mercury down and
helped to damp out any fluctuations from unwanted vibrations.  We could
handle up to a 12" mirror with a 14" diameter pan for the mercury.  In
practice, vibration was the killer as the mercury pool became unusable
when traffic was close by.  A truck 3 blocks away could send shivers onto
the pool and we were never able to cure the problem.  The mercury, which
had been borrowed from Grumman was returned and we substituted heavy
motor oil.  This worked OK but a very bright light source was needed due
to the number of reflections.  Another problem was keeping the oil
surface completely free of dust.  All these problems caused us to abandon
the setup and go back to the normal test arrangements.  Today, the
availability of very thin clear films such as used by Baader would allow
a dust cover over the oil and eliminate the dust problem.

Jarvis Krumbein

On Thu, 5 Jul 2007 12:23:23 +0200 "Vladimir Galogaza"
<vladimir.galogaza1@zg.t-com.hr> writes:
> Francis,
> 
> >The foucault test and the ronchi test may be performed 
> >with an autocollimator. However they become null tests 
> >which are much easier to interpret with an autocollimator than 
> without one
> >That is why I have become a fan of autocollimation.
> 
> One of autocollimation virtues is that the space required for 
> testing 
> is halved.
> Martti Koskimo once proposed a liquid surface in place of flat 
> mirror
> for test in autocollimation. Mirror to be tested is supported above 
> the
> pool of oil which serves as autocollimating  flat.
> I wander if somebody tried this. Should not be more complicated
> than interference test with mirror under the  surface of liquid.
> 
> Regards
> Vladimir.
> 
> 
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