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- To: owner-atm@shore.net
- Subject: BOUNCE atm@shore.net: Non-member submission from [OPTIXWIZ@aol.com]
- From: owner-atm@shore.net
- Date: Tue, 15 Oct 1996 04:48:25 -0400 (EDT)
>From atm-owner Tue Oct 15 04:48:22 1996 Received: from emout11.mail.aol.com (emout11.mx.aol.com [198.81.11.26]) by relay1.shore.net (8.7.5/8.7.3) with SMTP id EAA21759 for <atm@shore.net>; Tue, 15 Oct 1996 04:48:21 -0400 (EDT) From: OPTIXWIZ@aol.com Received: by emout11.mail.aol.com (8.6.12/8.6.12) id EAA27142; Tue, 15 Oct 1996 04:47:50 -0400 Date: Tue, 15 Oct 1996 04:47:50 -0400 Message-ID: <961015044749_127060357@emout11.mail.aol.com> To: epabcc@epa.ericsson.se cc: OPTIXWIZ@aol.com, atm@shore.net, rod_hiddleston@cpqm.saic.com Subject: Re: ATM Pic du Midi (08/15/96 posting!) Dear Bratislav, Sorry friend, but you've stepped in bullshit up to your waist this time! EVEN excellent BIG optics benefit from stopping down in "bad" seeing. A guy named David Fried (a bonafied genius) covered the analytics of this in OSA publications during the 60's and 70's for the benefit of stategic defense applications, initially. But he covered astronomical applications also. Basically, stop down until there is no major image blur, only image motion. That defines what astronomers call the seeing cell size, but Dave Fried called rho. Your best resolution for short integration times (.001 second to 0.03 second) will be with an aperture 5 times the rho aperture. And the resolution will be twice (2X) the diffraction limit of a rho aperture. So if you were at the "Pic" with a big refractor and rho were 100 mm, you would like to have an aperture of 500 mm to observe with, and you'd get resolution for a diffraction limited 200 mm aperture visually, or with a good CCD camera, if the latter were sensitive enough to get you an exposure in 0.001 second to 0.03 second (the shorter the better!) AND if the scale factor allowed you to meet the Nyquist Criterion (a minimum of two pixels per Airy disk or blur spot), IF your optics were diffraction-limited for the 500 mm aperture. So if the scope you were using were actually 600 mm, or a 1000 mm reflector, you'd stop down to the 500 mm for optimum results. Staying at 600 mm or larger will actually give INFERIOR results. (Fortunately, the "Pic" is one of the few places on the globe where excellent seeing can be had. Rho equal to 600 mm and larger has been seen at various times. Unfortunately, the "Pic" does not have a 3-meter diffraction-limited telescope to take "full" advantage of it!) If you were in my backyard, rho might only be 50 mm, so my "optimum maximum" aperture would be 250 mm. Remarkably close to what the "old heads" use to recommend, eh?! This IS NOT rocket science. Hundreds of folk worldwide know this stuff. But maybe not many of them are ATMs or astronomers. So, pass it on. Sorry I have not been part of the List lo these last few months, but other responsibilities have gotten in the way. I've been off the list since August something 'cause my e-mail was getting clogged with ATM List postings. Best wishes to you and my fellow ATMs, Gene Cross La Mirada, CA 310-941-9476
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