Any ATM worth his salt knows this, DT. On Oct 18, 2011 4:05 PM, "daniel turner" <outwest112@yahoo.com> wrote:
I checked my copy of Richard Suiter's book on Star testing and he has a chapter on the physics of the artificial star. Regardless of the type of source it needs to be moved a good distance away to avoid introducing an error. 20 times the focal length of the optic was once the standard but physics says that for faster and larger mirrors you could need more than 100 times the focal length.
The danger here is that you will proclaim a perfectly good parabola to be flawed, or worse you could carefully figure a prolate spheriod thinking it was a good parabola. Your own private reenactment of the Hubble Space telescope fiasco.
DT
________________________________ From: "erikhansen@thebluezone.net" <erikhansen@thebluezone.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 18, 2011 3:48 PM Subject: Re: [Utah-astronomy] ATM session report and next planned date
Maybe too much trouble for one time use, but if you do a lot of "star" testing it might be worthwhile.
Wow, that's an impressive setup for an artificial star!
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of erikhansen@thebluezone.net Sent: Tuesday, October 18, 2011 3:37 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] ATM session report and next planned date
Here is link about using a LED to build an artificial star, it does not seem to require more than about 100 ft of distance.
http://observatory.mvastro.org/library/Star_Test/ArtStar.html
On 10/18/11, Hutchings, Mat (H USA) <mat.hutchings@siemens.com> wrote:
Aw, come on, you can brave the cold at night in the winter!
Yeah, to a point, but then again, I am designing a heated observatory, so that's gotta tell you something... ;)
Re: Ronchi testing
With much experience, you can tell a lot with the Ronchi test. I used to hang-out with a local optical manufacturer, and we'd look at mirrors through the Ronchi. I would point-out problems that he had to stare and stare at, and most of the time he'd say "yeah, maybe..." until we star-tested it. Then he'd admit that I detected it with the grid.
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