Norbert reports: "I would have a telescope like the JMI NGT 12.5
but for a fraction of the cost. Base is the optical tube of a Meade
12" LightBridge Dobson. The tube is modified for a moderate
horseshoe mount: Declination wheels are shifted 100 mm (4 inches).
The self made rotatable top of the tube consists of sheet of 1 mm
aluminum instead of steel (lighter weight), attached with 3 spring
loaded toggle type fasteners. It was necessary to add a balance
weight."
Technical
Specifications: Type: Newtonian Aperture: 12 inch, f/5
Focal length: 1524 mm Weight of optical tube: 20 kg Balance
weight: 6,5 kg Weight of Mount: 20 kg Wood thickness: 24 mm
Horseshoe diameter: 752 mm (ca. 30 inches, made by router and
cycle) Driving roll diameter: 69,4 mm Angle polar axis
(latitude): 48°, adjustable EQ-3 stepping gear motor: n =
5,432/h ONDRIVE worm gear reducer: i = 12:1 Built: 2009
This telescope won
a first place award at International Telescopemeeting Vogelsberg
2009 (ITV 2009) Germany,
A lot of telescope for little money. The rotatable top of the modified tube
allows comfotable viewing of any part of the sky.
The Telescope
Prize winner at International Telescopemeeting Vogelsberg 2009 (ITV
2009) Germany Photo: Jasper Stein
Prize winning Scope at ITV 2009
Mechanical model, scale 1:10, for studying
Mechanical model, scale 1:10
The horseshoe mount disassembled in 2 parts without tools
Horseshoe Disassembled
Two Wooden rollers form the north bearing of the polar axis, horseshoe diameter 30 inches
Wooden Rollers support 30" Ring
Support bearing with roller and console
Support Bearing Close-up
Tube with balance weight, south bearing of the polar axis and precise adjustment in azimuth and polar declination
Tube with Balance Weight
Felt bearing for the declination wheels and the motion link with gear wheel and tension spring; declination is not motorized.
Felt bearing for Declination Axis
U-shaped distance holders prevents shifting of the tube on the declination axis.
Declination Axis Side Spacers
Friction gear for tracking with stepping gear motor and controller of an EQ-3 mount, worm gear reducer 12:1 (ondrives) and
driving roll with clamping clutch for tracking On/Off. Slipage prevented by water-resistant sand-paper (grain size 600) on driving roller.
Drive Roller with Clutch
Declination gear with a ratio of 1:4; the large gear wheel is a turned by a
toothed belt. The declination setting circle (diameter 5 inch) is calibrated on a star and to
find any object by its declination, pointing accuracy is within 7.5 arc-minutes (precise polar
alignment obligatory). Without gearing the Dec.-disk diameter whould have to be 20 inches.
