Cheap PushTo for a Dobsonian

A simple map compass with a rotating bezel as a functioning azimuth navigation system – and it’s even accurate to 1 degree! North alignment is not required.

Starhopping is of course the only true philosophy for us purist “Dobsonians”. But with very large hops or faint objects, sometimes it would be nice to know that we are heading in the right direction. For this purpose, the Dobsonian could be equipped with digital setting circles and a GoTo or PushTo solution. That would be the perfect answer, but there is also a much cheaper solution: all you need is a tube-mounted angle measuring device for elevation and a compass for azimuth.

Take a simple map compass, without sights or mirror, but with a rotating bezel. The divisions must be in degrees not hours; liquid-filled is recommended. You do not need to spend more than €20. Attach a holder for the compass to the rocker box, parallel to the tube. I used two rulers to make guide rails, which I fastened with double-sided tape.

The whole thing now works really simply: take the current position data for your “object of desire" from an astronomy app. Then set the desired azimuth on the bezel, place the compass in the guide rails and pan the Dobsonian until the compass rose or needle is parallel to the bezel – that’s it!

But beware: firstly, the magnetic north differs from the geographical north depending on the location; secondly, some Dobsonian tubes are made of sheet steel, which can cause deviations. However, this tends towards zero if you move the tube horizontally away from the compass for a short time. If preferred, you could also check this by means of a nearby guide star.

Accuracy is around 0.5 to 1 degree – more than enough for visual observation. And just about the most beautiful thing about it: north alignment is not necessary! I wish you lots of fun with your new PushTo navigation on a shoestring.

Author: Jan Willem Robert / License: Oculum Verlag GmbH