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favourite this post 20" SCHMIDT CASSEGRAIN TELESCOPE 25" PRIMARY 9.5IN SECONDARY MIRROR SE - £2600 hide this posting unhide

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make/manufacturer: SCHMIDT
model name/number: CASSEGRAIN TELESCOPE 25"

Mirror set removed from a never used NASA optical device. Originally believed to be a DK or RC mirror set however after closer examination it appears it may be a fast 20in schmidt cassegrain telescope with a missing corrector but not 100% sure. Might make a good ATM base for a DK or RC telescope design otherwise make corrector for it. I'm working to get the exact specifications if possible will update info. It appears the primary is f/1 and the secondary has a 42.7in radius giving the system ~f/2.6

Primary is held in a cradle that was machined from a solid chunk of AL. Cradle is 4 in thick with a 5/8in rim with a ~26.5OD and overall 26.75inOD. Back side will accept a disc that is 24inD and 1/4in thick, center hole 22 7/8D and 3/8 thick. The mirror appears to be made of Pyrex, 25.75OD, center hole is 5in ID and the glass is 1in thick at the hole, apx 2.5in thick at the edge. The mirror is in excellent shape overall. It is held in the cradle via several silicone spots as seen in pictures with small spacers all around the rim. Assembly is 90lb. Heavy AL disc back is 28 3/8in D x 1/2in thick and is 32lb, it was fixed to the mirror assemble via 3 bolts and nylon washers, both AL parts have numerous drilled and tapped holes.

Secondary has a heavy duty mount with 3 point adjustments and 20inD spider. 9.5inD mirror is in excellent shape but a couple very fine scratches you can see in picture.

A professional briefly looked at the mirror made rough estimate the design was a fast 20" Cassegrain System ~f/2.6

Other possible uses, as a Hindle sphere for testing and figuring cassegrain secondaries. Also in the Waineo null test for concave aspheric mirrors ( ie parabolas) You can also make a lensless Schmidt camera with it.

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post id: 6789732613

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