[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
RE: Rayleigh Water Test (Was: Re: [ATM] 30" Flats)
I would think that the cohesive forces in a liquid could cause a distortion
in the surface. (Foe example a drop of water on most surfaces is usually not
spread flat but is a ellipsoid configuration or thereabouts. Also depending
on the container walls the liquid can actually be pulled up or pushed down
near the wall. Wouldn't this mean that great care is needed to get
compatible type of container, type of liquid, the percentage of useful flat
surface declines. etc.. I believe this led to having to spin mecury in
order to get a reasonable flat surface.
Jerry Reddell
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf
Of matt
Sent: Thursday, February 17, 2005 10:24 AM
To: vorblesnak@peak.org; atm@atmlist.net
Subject: Re: Rayleigh Water Test (Was: Re: [ATM] 30" Flats)
OK, so let's narrow down the issues a little:
- vibration from outside sources - how about a viscous liquid, in a baffled
container, with solid heavy walls, placed on top of a vibration reducing
support ? The usual thing people do with their optical bench stuff, place it
on top of air bags, sorbothane pads etc .
-mirror in unnatural position -valid concern for thin mirrors that are not
RTV'ed to the mirror cell. Narrowing it down to either thicker mirrors , or
thin mirrors that are glued to their support, this would then cease to be a
problem.
Anything else ? I'm tempted to give it a try before I try the hard way, with
making 3 large flats etc.
best regards,
matt tudor
-----Original Message-----
From: vorblesnak@peak.org <vorblesnak@peak.org>
To: atm@atmlist.net <atm@atmlist.net>
Date: Thursday, February 17, 2005 11:08 AM
Subject: Rayleigh Water Test (Was: Re: [ATM] 30" Flats)
>Ingalls addressed this in a article in Scientific American. The primary
>problem seemed to be vibration from outside sources. He noted that the
>train on the track some distance away, caused ripples in the fringes when
>using it to test a flat. One suggestion was to use a very viscous liquid,
>heavy oil etc, and dampen the liquid flat well. Even then you must allow
>it to settle down. The other problem was it placed the mirror in an
>unnatural position and in large mirrors sag became an issue. Rarely do we
>look at our toes with a 30" newt.
>
>David Davis
>Toledo, OR
>
>
>> Speaking of flats, is there any quality up to date information of how to
>> use a liquid as the reference flat ?
>> In theory it would be very simple and inexpensive to place the
>> interferometer in the telescope focuser/eyepiece holder, turn the scope
>> vertical on its equatorial mount or a make shift test stand, and point it
>> straight down at a liquid surface . This would become an instrument
double
>> pass autocollimation test . Why aren't ATM's using it and instead are
>> laboring to make large flats or pay many thousands to acquire same large
>> flats ?
>
>
>_______________________________________________
>ATM mailing list http://www.atmlist.net/
>
_______________________________________________
ATM mailing list http://www.atmlist.net/
_______________________________________________
ATM mailing list http://www.atmlist.net/