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nytecam
Postmaster
Reged: 08/20/05
Posts: 5741
Loc: London UK
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In a letter by optician John Wall [Crayford mount/ large dialyte refractor etc] in the current BAA Journal [119,3,2009] he reports a new refractor system using a large long focus [single element non-archromatic] objective before a smaller short focus positive achromat with overall good correction for chromatic abberation [CA] for the combo. He quotes CA of the single element OG is reduced 95%. 
Anyone tried something along these lines 
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Nytecam 51N 0.1W
Meade 30cm LX200+ETX-70+e-finder+C8+Ha+CaK PSTs SBIG SGS+homebuilt spectrographs
Starlight SXVF_M9+Lodestar CCDs/Canon 300D DSLR/Fuji E550
My observatory build-ETX-70 imaging-my videos
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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A Schupmann is simpler to build and offer 100% color correction with a polychromatic Strehl 0.997 in may cases It also uses a singlet objective but only the addition optics are a small spherical mirror and menicus corrector lens. I'm working on my third set of schupmann optics. The design gives amazingly sharp images since there is no obstruction,coma and is super well color corrected.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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nytecam
Postmaster
Reged: 08/20/05
Posts: 5741
Loc: London UK
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Quote:
A Schupmann is simpler to build - Dave
How simple is simple The Wall new scope is incredible simple 
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Nytecam 51N 0.1W
Meade 30cm LX200+ETX-70+e-finder+C8+Ha+CaK PSTs SBIG SGS+homebuilt spectrographs
Starlight SXVF_M9+Lodestar CCDs/Canon 300D DSLR/Fuji E550
My observatory build-ETX-70 imaging-my videos
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Mike I. Jones
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Reged: 07/02/06
Posts: 1571
Loc: Fort Worth TX
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Nytecam, if you can locate the prescription for Wall's dialyte in the BAA Journal, please post it and we can all have a ZEMAX/OSLO look at it. I haven't had much luck getting really good optical correction for the particular configuration you describe, not for any usable field diameter (lots of field curvature).
I think the Schupmanns, Ed Jones's Chief systems, and the Seymour Rosin corrected hyperboloid systems are a simpler way to go, with far better broadband correction at larger apertures and flat, CCD/DSLR-sized fields.
Mike
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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Quote:
Quote:
A Schupmann is simpler to build - Dave
How simple is simple The Wall new scope is incredible simple
Very simple, it only has three elements, a double convex singlet objective, a meniscus correcting lens and a 1" diameter spherical mirror. Both lenses are made from the least inexpensive optical glass, which is BK-7. The Super Schupmann design has all spherical optics. The unit I'm making now has poly-strehl of 0.997 and is diffraction limited to 1/2 a degree field. The results have been confirmed by OLSO and Zemax and many designs are in the public domain.
Wall's uses a 5 element corrector made of a number of different glass types in addition to a singlet element objective, two optical flats and a field lens.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4927
Loc: MA
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I haven't studied this, but if a Schupman indeed has zero color then the lens material doesn't matter, right?
Schupmans and Schiefs are cool designs, but not cool enough to ever be commercially produced, evidently.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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In theory is doesn't matter what the glass type is in a Schupmann, only that both the objective and the corrector lens are made from the same glass. There are public domain designs for ones that use quartz which extends the wavelength range into the UV. Since a light crown works well, BK-7 is the material of choice, since the performance is excellent that cost of the material is the least expensive.
Schiefspieglers have been available commerically for years. A company in Germany sold them for years, in the USA I believe Cal Astro Optics and Torus Optics sold mirror sets for years and AOK Swiss sells complete OTA now.
While I don't know of any commerical Schumpmann optics, Astro-Physic new astrograph is a version of Schupmann known as a Honder and outlined in Jim Daley's book on Schupmanns. The spot diagram is very impressive.
Here is a spot diagram for a 6" f/12 that I finished the optics for a few months ago. It shows that all the colors fall well within the airy disk and the 1/2 degree field is well corrected.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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