http://tech.groups.yahoo.com/group/schupmann/ Schupmann Tue, 12 Jan 2010 22:43:00 GMT phil_herring http://tech.groups.yahoo.com/group/schupmann/message/1173 http://tech.groups.yahoo.com/group/schupmann/message/1173 Thanks for the excellent reply, Jim! My rationale for using a field lens rather than a mirror is that it's one thing that I can probably buy at a reasonable Tue, 12 Jan 2010 11:56:54 GMT James A. Daley http://tech.groups.yahoo.com/group/schupmann/message/1172 http://tech.groups.yahoo.com/group/schupmann/message/1172 Hi Phil, You can make the field lens out of any optical glass that will take a fine polish. My nearly completed 14-inch medial utilizes a fused silica Tue, 12 Jan 2010 07:34:10 GMT phil_herring http://tech.groups.yahoo.com/group/schupmann/message/1171 http://tech.groups.yahoo.com/group/schupmann/message/1171 I've read a fair bit now about the Schupmann design, but most articles don't seem to discuss the field lens in great detail. So: does the field lens have to be Tue, 12 Jan 2010 01:00:28 GMT James A. Daley http://tech.groups.yahoo.com/group/schupmann/message/1170 http://tech.groups.yahoo.com/group/schupmann/message/1170 Thanks Bert; that sure leaves out silicon as the worst thing one can do with stellar coronagraphs is to work them in the violet because scattering from every Mon, 11 Jan 2010 22:26:07 GMT Willard, Berton - 1006 - MITLL http://tech.groups.yahoo.com/group/schupmann/message/1169 http://tech.groups.yahoo.com/group/schupmann/message/1169 Silicon reflects only about 30% at 700 nm, peaking to about 70% in the uv. Google "silicon reflectivity" Bert. On 1/11/10 4:51 PM, "James A. Daley" Mon, 11 Jan 2010 21:55:40 GMT James A. Daley http://tech.groups.yahoo.com/group/schupmann/message/1168 http://tech.groups.yahoo.com/group/schupmann/message/1168 Bert, The silicon mirror idea sounds very interesting and I would like give it a trial test. I think that among the local opticians some good polishing hints Mon, 11 Jan 2010 16:55:47 GMT Willard, Berton - 1006 - MITLL http://tech.groups.yahoo.com/group/schupmann/message/1167 http://tech.groups.yahoo.com/group/schupmann/message/1167 Here are a couple of sites to check out. I've never found a good reference for comparing measured BRDF of mirrors. If you find something interesting let me Sun, 10 Jan 2010 02:49:33 GMT Arnold Ashcraft http://tech.groups.yahoo.com/group/schupmann/message/1166 http://tech.groups.yahoo.com/group/schupmann/message/1166 Jim: I have been searching online for the measurements, but all the hits I find are in Journals I can't access. Very frustrating. The abstract almost gives Sat, 09 Jan 2010 21:00:43 GMT James A. Daley http://tech.groups.yahoo.com/group/schupmann/message/1165 http://tech.groups.yahoo.com/group/schupmann/message/1165 Hi all, I wonder if anyone on the list has used Rhodium for a reflecting mirror coating? I am performing special measurements on large delta m double stars Thu, 03 Dec 2009 18:50:35 GMT David http://tech.groups.yahoo.com/group/schupmann/message/1164 http://tech.groups.yahoo.com/group/schupmann/message/1164 John, Schupmann optics are pretty rare. I only know of two set that have exchanged hands in the last 10 years. I would guess that a commerical shop would Thu, 03 Dec 2009 09:01:34 GMT johnny999_99 http://tech.groups.yahoo.com/group/schupmann/message/1163 http://tech.groups.yahoo.com/group/schupmann/message/1163 Hello, Does anyone know of opticians who are amenable to making a Schupmann optics set, or if there are complete telescopes for sale? Thanks John Wed, 02 Dec 2009 00:13:06 GMT James A. Daley http://tech.groups.yahoo.com/group/schupmann/message/1162 http://tech.groups.yahoo.com/group/schupmann/message/1162 Hi John, The thickness of a Schupmann objective is not optically critical but if too thin it will be overly flexible and could lead to polishing and figuring Tue, 01 Dec 2009 03:00:47 GMT johnny999_99 http://tech.groups.yahoo.com/group/schupmann/message/1161 http://tech.groups.yahoo.com/group/schupmann/message/1161 In a circa 2007 thread, there was a reference to a Schupmann in Canada. Since I am there (here, in Toronto) most of the time - does anyone know where it is? Mon, 30 Nov 2009 20:27:51 GMT johnny999_99 http://tech.groups.yahoo.com/group/schupmann/message/1160 http://tech.groups.yahoo.com/group/schupmann/message/1160 Thanks guys - I will keep my eyes peeled for BK-7 or BSC-2 blanks. No need to be penny wise and pound foolish. What range of thicknesses would match up for Mon, 30 Nov 2009 14:55:31 GMT David M Groski http://tech.groups.yahoo.com/group/schupmann/message/1159 http://tech.groups.yahoo.com/group/schupmann/message/1159 Hi John, With OSLO and knowing the RI of the flint I'm sure one can come up with acceptable design. Personally I would keep my eyes open for BK-7 or BSC-2,