[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: [ATM] Autocollimation Oil Test
Hello Gary,
The method with the small hole in the center of the oil flat is the most
tempting.
All errors you see are only from the mirror you test and from collimating
errors.
The elliptical flats errors and it's collimating errors do not spoil the
accuracy of the test.
the test is just like using normal Glass flat with a small hole in the
center of the flat mirror in horizontal position.
This is the way many pros test their mirrors but in this there is that
always present problem of twisted mirror
when the mirror is in testing stand.
In oilflat test the twisting of mirror is essentially smaller and easily
predicted (using PLOP etc.)
( Only that Elevation is depression )
There are two uncoated reflections ( Glass + oil ) and the intensity is
reduced say by factor 1/400.
Of course you don't need a laser although laser collimator is very helpful
in collimation.
If laser is used the beam is expanded to illuminate the whole mirror.
I use spatial filter ( microscope objective and a pinhole ) but this is
needed only for interferometer.
As always with lasers you should be careful.
Ronchi test is the easiest. You can use bright led directly through the
Ronchi screen (slitless arrangement ) and
there is plenty of light.
Any telescope ( some need modified support for the main mirror ) with
oilflat test and a Ronchi you see a lot of the quality of the whole
telescope and if you look at the interference effects of normal Ronchi you
can use it as a simplified interference test ( TEXEREAU page 73 )
Martti Koskimo
----- Original Message -----
From: "GF" <gary@rcn.com>
To: "Martti Koskimo" <martti.koskimo@kolumbus.fi>
Sent: Saturday, January 21, 2006 5:30 PM
Subject: Re: [ATM] Autocollimation Oil Test
> Hello Martti,
>
> Thank you for the description. I'm particulary interested in the method
> with the hole in the center of the oil. Is the laser diffused? If not, is
> there any danger from the beam?
>
> Regards,
>
> Gary Fuchs
> USA
>
_______________________________________________
ATM mailing list http://www.atmlist.net/