Orange Tube C8, Tasco 7te-5, 4" Criterion Dynascope, Jason/Towa 313
Nikon Action Extreme & Pentax WPii Binoculars
At my club, everything one could want up to 18"
Paul Maxson Celestron C14, Mewlon 250, Orion EON120, Flea3, ASI120MM. Those who say it can't be done need to stay out of the way of those doing it. http://www.sunspot51.com
David Cotterell Toronto, Ontario "If an observer actually sees an object, there is no point in referring to a formula to find out whether he ought to see it; and if he fails to detect it, no formula will ensure his success." - W.H. Steavenson 8" f/15.5 TEC Maksutov 16" f/5 Teeter/Zambuto Dob 66mm WO SD AT 65EDQ APO Refractor Astro-Physics Mach 1 GTO Mount iOptron ZEQ25 mount Canon 60Da
"The White Zone is for loading or unloading of passengers only. No Astrophotography." Cosmic Acres! Greatest restoration challenge: Tulley and Sons 3" achromat on Altazimuth mount, circa ~late 1820s
Quote:Looks like a DFM:-Tim.
Quote:0.64-m (25-inch) f/9.6 Ritchey-Chrétien OTAOur unique, high-resolution primary and secondary mirrors are made from zero-expansion-coefficient substrate. They were custom-figured in 2002 for the Clay Center Observatory by world-class opticians at Brashear LP in Pittsburgh, Pennsylvania. Taking more than one year to figure and polish, they provide diffraction-limited performance and a wide, flat field. The full-thickness Zerodur primary is an f/2.8 hyperboloid figured to 1/90 wave RMS at 632.8 nm. The Astrositall hyperboloid secondary has a surface figure of 1/100 wave RMS at 632.8 nm. The optical tube features computer-controlled aperture doors, as well as two sets of primary and secondary baffles. Users can select either a 2-inch-diameter unvignetted field with minimal central obstruction or a 4-inch-diameter unvignetted field with a slightly larger central obstruction. The combination of superb optics and good local seeing enables the 25-inch telescope to produce sharper images than telescopes several times its size.
---John 14.5" Dall-Kirkham w/Royce optics Celestron 11 AP140EDF,TEC140,Tak FS60-C ZWO ASI120MM and ASI120MC DMK21AU618.AS SBIG ST-10XE http://www.spacescenes.com
Quote:Funny thing about this school is that for less money, they could have built a better free-standing observatory.
Quote:What's a "DFM?"I posted this in Cats and Cassess because of the scope itself. Another thread described the implausibility of building a 1/10 wave C8, even if the mirror itself were 1/10 wave. The difficulties aligning the optics were just too great. The current scope is not a C8, but apparently C8's big cousin. Wouldn't the same issues apply? And, about the 60-foot pier: Homework completed or not, could such a tall pier really be adequately steady? Wouldn't the sway so far from the ground blur the images?
- Jared Willson
16" F/12 R-C with optics figured by Paul Jones mounted on Byers Research Grade Series II mount with Gemini II GOTO housed in 11.5' Sirius Observatory; C11 on G11;a few Ethoi and other longer focal length Televue eyepieces in the 2" format; a 6" F/10 refractor for which I made the achromatic objective.
Quote:Hi Joe,Good luck with the job!It looks like an excellent facility with some interesting research and education programs, I'm sure you could have a lot of fun there. The 25 inch looks like a very impressive scope - let us know what you find out about the mirror specs and the thermal properties of the rooftop dome when you start!Cheers,Keith
Quote:Have you ascertained if this figure is a P/V or RMS value? The distinction is most significant.
Quote:Why do they discuss the accuracy of each element? Isn't the total system performance more important? Star Instruments gives an analysis of the combined system (double pass auto-collimation interferometric analysis) on their R-C optics sets. If the mirrors are made independently and not tested together, the combined system performance could be much less.
Quote:RMS = Root Mean Square. It is the magnitude of the average deviation of error. Take measurements at 1,000 points, for example... Some will be negative and some positive. Square them to force them all to be positive. Average the 1,000 values together. Then take the square root (to offset your previous "squaring"). It lets you know how far from perfection a randomly selected point will be.PTV or P/V = Peak to Valley. It is the measurement of the largest deviation from perfection across the entire surface or wavefront.Obviously, for a given optic, the PTV number will be worse since it is a measurement of the biggest error rather than the average error. PTV has generally been considered the gold standard for assessing optical quality since it is almost impossible to create an optic with a low PTV but a high RMS. In practice, either value will likely give you a good prediction of the other. Any time you see values better than, say, 1/20th wave you are almost certainly talking RMS rather than PTV.
12.5" Home built F-4.8 Eq Newt. Lightholder Optics mirror 12'x12' roll-off roof observatory 6" Home built f-6 Newt. w/Dick Wessling mirror on CG-5 Eq. mount. 4.5" Orion Starblast My equipment philosophy... If it ain't broke, fix it anyway.