-- With Regards, Mel Bartels Programmer/Analyst, and amateur astronomer mailto: mbartels@efn.org homepage: http://www.efn.org/~mbartels How To Computerize A Dob: http://zebu.uoregon.edu/~mbartels/altaz/altaz.html
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- To: owner-atm@shore.net
- Subject: BOUNCE atm@shore.net: Admin request
- From: owner-atm@shore.net
- Date: Thu, 26 Sep 1996 17:02:04 -0400 (EDT)
>From atm-owner Thu Sep 26 17:01:59 1996 Received: from pine.ucs.uwplatt.edu (pine.ucs.uwplatt.edu [137.104.128.2]) by relay1.shore.net (8.7.5/8.7.3) with ESMTP id RAA08808 for <atm@shore.net>; Thu, 26 Sep 1996 17:01:56 -0400 (EDT) Received: from uwplatt.edu by uwplatt.edu (PMDF V5.0-6 #17356) id <01I9XTXG33W0APWHQR@uwplatt.edu> for atm@shore.net; Thu, 26 Sep 1996 16:03:27 -0500 (CDT) Date: Thu, 26 Sep 1996 16:03:27 -0500 (CDT) From: Adrian Pederson <PEDERSON@uwplatt.edu> Subject: Help with Foucault test To: atm@shore.net Message-id: <01I9XTXG591UAPWHQR@uwplatt.edu> X-VMS-To: IN%"atm@shore.net" MIME-version: 1.0 Content-type: TEXT/PLAIN; CHARSET=US-ASCII Content-transfer-encoding: 7BIT Hello again, I have not posted here for awhile but my first mirror, an 8", ~f5.5, is now almost polished out. There is still an outer ring about 1/4" wide which shows some faint grinding marks. Anyway, I am having trouble with the Foucault test. I would like to be able to see if I'm anywhere near spherical currently, and also just to get a feel for the test. I'm currently using the Dakin type tester, I believe it's also called a slitless tester. It is set up almost exactly like the picture on p.271 of Optical Shop Testing by Malacara, except the bulb is mounted directly behind the knife edge. The knife-edge is horizontal with the bulb on the right edge of the blade, it is mounted at a semi-fixed height on a two-axis positioning table. When setup like this how do you move the knife-edge to cut into the rays? This is kind of confusing to me, since the light source is also moving. I can see shadow patterns by moving by eye up and down behind the knife, these also appear to cut from the bottom or top depending on how far behind the knife I place my eye, this is without moving the knife at all. It is also hard to hold my head still, causing the shadows to dance around. It seems that it should be the knife and not my eye position that creates the shadows since it will be rather hard to measure my eye position. Can someone tell me a step-by-step procedure for simply finding the focal length with this type of tester. I appreciate any help I can get on this. Adrian Pederson pederson@uwplatt.edu
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