100 mm f/4.2 Rich Field Refractor

Built by Guido Fuhrmann of Schloss Holte-Stukenbrock, Germany

One day I found an old Pentascop projector which had a really fancy Meyer Görlitz Lens with 420 mm / F3.6. The lens design is a Cooke Triplet. After investigating a bit about this heavy (3.5kg) beauty I found out that it could be a nice Richfield scope. So I gave it a go.

After a first test setup it was clear that I wouldn´t be able to use the full 117mm (f3.6) lens diameter, so I stopped it down on 100mm (f4.2). Because of the short light cone I had to use a 2” newton focuser. All necessary parts as focuser base, baffles and some parts of the zenith mirror are made out of PETG on a 3d-printer.

The wood for the parallelogram mount came from an old bed and some other parts I found in my workshop. Because of the 7kg counterweight and the 5kg of the scope the mount runs very smooth without shaking at all. Even moderate wind has not much effect on the system.

The first light was a real pleasure. Round stars over 2/3 of the field. At the corners only slight deformed stars which is expected. Eyepieces from 32 mm to 20 mm work really fantastic but under 20mm the optical errors become too much.

Anyway it became a really cool Milky Way cruser and I´m looking forward to summer when North American nebula is up - itt should fit completely into the field of view.

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