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- To: owner-atm@shore.net
- Subject: BOUNCE atm@shore.net: Non-member submission from ["Mark VandeWettering" <markv@tick>]
- From: owner-atm@shore.net
- Date: Mon, 21 Oct 1996 16:36:27 -0400 (EDT)
>From atm-owner Mon Oct 21 16:36:15 1996 Received: from tick.pixar.com (tick.pixar.com [138.72.30.65]) by relay1.shore.net (8.7.5/8.7.3) with SMTP id QAA11614 for <atm@shore.net>; Mon, 21 Oct 1996 16:36:14 -0400 (EDT) Received: by tick.pixar.com (Smail3.1.28.1 #15) id m0vFR4Y-0007UmC; Mon, 21 Oct 96 13:35 PDT From: "Mark VandeWettering" <markv@tick> Message-Id: <9610211335.ZM19242@tick> Date: Mon, 21 Oct 1996 13:35:42 -0700 In-Reply-To: Fraser Clarke <fjc3@st-andrews.ac.uk> "Re: ATM Re: 4.25" Wing-nut idea..." (Oct 21, 12:28pm) References: <Pine.SOL.3.95.961021122521.14661C-100000@pesto> Reply-To: markv@pixar.com X-Mailer: Z-Mail (3.2.0 26oct94 MediaMail) To: Fraser Clarke <fjc3@st-andrews.ac.uk>, Brand <huntb@ucs.orst.edu> Subject: Re: ATM Re: 4.25" Wing-nut idea... Cc: faintfuzzy@worldnet.att.net, atm@shore.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii On Oct 21, 12:28pm, Fraser Clarke wrote: > Subject: Re: ATM Re: 4.25" Wing-nut idea... > I think that I read something in S&T about dping the same sort of thing > with resistors (in series) around the edge of the mirror to correct for an > undercorrected mirror. I don't suppose this would give enough expansion > for what you want to do, but it might be a jolly good idea for longer f > scopes??????, if the expansion would work out to be a parabola. > Any thoughts??? > BYe Nothing like opening with a good inflammatory statement: This idea sucks. :) I read the article in question, and I was (and still am) exceedingly skeptical about the claims made for its effectiveness. A number of my criticisms are: 1) introduction of heat in the tube is probably the last thing you want unless there is some overwhelming need for it (like dew prevention). It doesn't take much a change in air temperature within the tube to induce a magic quarter-lambda shift in the wavefront. Its just a bad idea. 2) regardless of what the author claimed, glass is an exceedingly good insulator, and I remain skeptical that the mirror can be "tuned" in near real time by the application of small amounts of heat. 3) such tuning only remains effective while the mirrors surface is undergoing heating and cooling. Therefore, more and more heat needs to be applied to maintain the figure as the mirror heats up. Bad idea. I wish Sky & Telescope was a bit more skeptical about some of the stuff they publish in their Telescope Making column. This was about the third bogus or semi-bogus idea which has graced their pages lately. Mark -- Mark T. VandeWettering Telescope Information (and more) Email: <markv@pixar.com> http://webspace.com/markv/ <markv@webspace.com> Clear Skies!
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