Brent, I confess I don't know, only that it delivers what I consider a great image. What's the best/easiest method to determine the figure? Rich --- Brent Watson <brentjwatson@yahoo.com> wrote:

Rich,

I had a 6" Dynascope at one time. I found it in a pawn shop. The mirror was so dirty I was not sure there was a mirror in the scope at all! I tested the mirror and found it was a great sphere. Tha't OK if you want a sphere, but a parabola at f8 is quite different than a sphere - at least 1/2 wave. I have always wondered if it was just that scope, or were all Dynascopes spheres? How about yours? Chuck - is yours a sphere?

Brent

--- Richard Tenney <retenney@yahoo.com> wrote:

...

Got the following from a fellow on the Criterion Dynascope list today. Amazing webcam image obtained from this humble classic 6-inch newtonian (I'm still the original owner of a vintage 1972 RV-6, still my preferred grab-n-go scope)...

---------------------------------------------------

...

This was captured with a Philips ToUcam Pro webcam through a Tele Vue 2x barlow with an extension tube:

http://www.unm.edu/~abqtom/images/Planets/Saturn/2004-03-22-TEW-Sat.jpg

...

__________________________________ Do you Yahoo!? Yahoo! Finance Tax Center - File online. File on time. http://taxes.yahoo.com/filing.html

_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com

http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy

...

Visit the Photo Gallery: http://www.utahastronomy.com

__________________________________ Do you Yahoo!? Yahoo! Finance Tax Center - File online. File on time. http://taxes.yahoo.com/filing.html

_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com

http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy

Visit the Photo Gallery: http://www.utahastronomy.com

__________________________________ Do you Yahoo!? Yahoo! Finance Tax Center - File online. File on time. http://taxes.yahoo.com/filing.html

--- Brent Watson <brentjwatson@yahoo.com> wrote:

you can look at the diffraction patterns on either side of focus.

That's probably the easiest/quickest way if he doesn't have a Ronchi. I believe there are patterns on the Web somewhere, for comparison purposes, if Suiter's book isn't at hand.

I have always suspected the RV-6 I had was an "escape". (Escaped the figuring process.)

I once talked at length about this with Paul Rini. According to him, and as best as I can remember, many of the trained optical workers in the area "made the rounds" between telescope/optical manufacturers, eventually working for all of them at one time or another, and sometimes moonlighting simultaneously. Not all the opticians were of equal ability, either. Some had exceptional talent, Paul mentioned a Jeff Hunter who supposedly put out some of the best mirrors that Edmund, in this instance, ever sold. He actually would parabolize f/10 production mirrors. So there is the possibility that some RV-6 mirrors were made by a higher-grade worker than others. My own personal experience with Criterion in the 1970's was unpleasant; they could not deliver my order even after one year of delay, on an original one month promise. I recall several frustrating telephone conversations with Mr. Krewalk. Even then the company was in decline. They eventually sold out to B&L on the strength of their SCT line, which Celestron & Meade crushed to death in the marketplace. The best 6" Dynascopes I have ever seen were sixties vintage, the only 8" Dynascope I ever saw was fifties vintage (and beautiful to behold, let me tell you.) Lastly, the 6" Dynascope tube is undersized. Rising thermal currents don't have much room to stay out of the optical path. But, all that aside, I too have seen some excellent imagery from 6" Dynascopes. And I always thought they looked darn cool. Sorry to wax nostalgic. C. __________________________________ Do you Yahoo!? Yahoo! Small Business $15K Web Design Giveaway http://promotions.yahoo.com/design_giveaway/