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- To: owner-atm@shore.net
- Subject: BOUNCE atm@shore.net: Non-member submission from [btk@ix.netcom.com (Bill Marriott )]
- From: owner-atm@shore.net
- Date: Thu, 31 Oct 1996 17:28:35 -0500 (EST)
>From atm-owner Thu Oct 31 17:28:29 1996 Received: from dfw-ix4.ix.netcom.com (dfw-ix4.ix.netcom.com [206.214.98.4]) by relay1.shore.net (8.7.5/8.7.3) with SMTP id RAA08726 for <atm@shore.net>; Thu, 31 Oct 1996 17:28:28 -0500 (EST) Received: from (btk@sfo-ca7-20.ix.netcom.com [204.30.64.52]) by dfw-ix4.ix.netcom.com (8.6.13/8.6.12) with SMTP id OAA06389 for <atm@shore.net>; Thu, 31 Oct 1996 14:27:49 -0800 Date: Thu, 31 Oct 1996 14:27:49 -0800 Message-Id: <199610312227.OAA06389@dfw-ix4.ix.netcom.com> From: btk@ix.netcom.com (Bill Marriott ) Subject: MakNewt Project To: atm@shore.net Well, the Cassagrain still is sitting, waiting for the new workshop to be built, which is going nowhere as we have a new baby, so, time to make some more optics. In response to discussions about refractors several months ago (which has come up again recently I've seen), and planetary optics, comments are usually raised at this point (usually by Bratislav) about how a longer focus newtonian is possibly the more efficient way to go, in terms of ease of construction, and ability to make perfect optics. So, with some design help from Bratislav I am putting together a f8 6" Newtonian, with a Maksutov corrector, which if it works out should produce an excellent planatary scope, as secondary will be fairly small, <1.25", which will be mounted through the center of the corrector, so no diffraction spikes, and a closed tube to boot, along with the excellent image produced by the Maksutov design, as well as a primary made of Cervit. This is a trial version of the 12" MakNewt I hope to make in the not to distant future. (I have the blank for the 12" corrector, but need to come up with some kind of a generator to dig out the 1" sag needed!) So, the topic of the day is fabrication of the meniscus. I have done some reading, in Mackintosh's ATMT,looked thu TM magazine, (not much there) I suspect there are some S&T references, ( suggestions?), and I have a copy of Warren Filmore's article on Mak construction. The article with the most info on Maksutov meniscus fabrication is A.J. Blackwood article in ATMT vol. 1. My area of greatest concern is hitting the proper RC and thickness for the corrector, though I have been lead to believe that tolerances are more forgiving for the Newtonian version of the Maksutov. Blackwood's article goes into detail about changes in RC as one changes grit, and differences between TOT and MOT. Any further comments on this from those out there who have dealt with this issue would be greatly appreciated. Starting out, I'm first attempting the concave side of the meniscus. I have set up one of the one-armed bandits at work as a pseudo generator. Tool is on bottom, consisting of a 6" pyrex disc, cross hatched approx. .300" deep with 1" squares. The overarm is pulled out till the stroke approximates a chordal stroke, with the center of the corrector blank approx. 1/2" to 3/4" from the edge of the tool, the arm makes a short 2" stroke, and the spindle is running at approx. 120 RPM. I was concerned that the approx. .275 sag would take forever, but with 20lbs of weight and 80 grit, 45 minutes of grinding time put the sag at 75% of desired value, not to bad!, another 15 minutes & I should be close. Then I was going to try to finish R1 and flash polish to check focal length. Blackwood goes into detail about hitting fl. by sphereometer alone, which concerns me as my sphereometer that has the range needed is only accurate to .0005" or so, while my really accurate sphereometer (.0001") only has a range of approx. .030, so how to link the two is the question, or with the MakNewt design, maybe the .0005" accuracy is sufficient. Once again, comments are appreciated. Once R1 is done, then I was going to block the corrector concave side down on a blocking pyrex, and mill the other side parallel, which should center the curve??? Then with the corrector on a level surface, concave side up, I would think that by putting a small ball bearing in the middle of the corrector, it will find the center, which will allow me to mark and then core out the 1/2" hole for the secondary mounting, before I start the convex side of the corrector. Since the center hole will be less than half the size of the secondary, I don't think any roll off of the figure into the hole will be of any consequence. Comments? Anyway, seems fairly straight forward at this point, we'll see where it goes. Bill Marriott Woodacre, Ca. USA btk@pacbell.net
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