18” Ultra Compact



  18” f4.5 (mirror set shared with my observatory scope)
  Feathertouch Focuser with integrated Paracor, (SIPS)


  Total Weight; about 30kg
  Size; will fit in the boot of my car, (except truss poles!)
  Max eyepiece height; 2.1 metres
  Truss poles; 20mm Al tubes covered in black heat shrink.


  Geared stepper motors driving through toothed belts
  40000 tick encoders 
  Nexus DSC for  scope position readout
  SkySafari for telescope control
  Raspberry PI driving stepper motors via Phidget modules 
  Plate-solving digital finder finishes goto’s to 1 arc min.

This scope has been a 10 year journey, striving to reach ultimate performance in a size and weight that can be transported in my car.


Phase 1: The mirrors were removed from my observtaory equatoria fork mount and the basic UC design took shape. Ithad the usual ptfe (Teflon) pads for bearings. 


Phase 2: testing with the servos showed that the PTFE bearings were giving too much friction. I  replaced them with ball bearings and now it runs very smoothly and easily. Added the encoders, wifi link and starting to finish off the wiring and installation of ancillaries.

IMG 0953

Phase 3: Having proved the drive system to work very well, the decision was made to go into small scale series production! Working with a friend we designed a compact unit built into a high quality aluminium case, laser etched panels and improved user setup and interface. 

IMG 0976

Phase 4: Modifications were undertaken between 2017 and 2019.

Changed from 'toothed wheel drive’ to ‘toothed belt drive’. Although not as elegant the performance is so much better. At the same time I introduced clutches on both axes. the scope can now be simply pushed to a new location in the sky, and the tracking drive automatically recalculates and takes over at the new position.

Screenshot 2023-01-26 at 17.14.17

Phase 5: Squeezing everything into my new Mustang was getting tedious, so a rebuild was undertaken to make the scope more compact when being transported, and a bit stiffer in winds. 

The Altitude drive is now via rollers on both trunnions. This gives superb motion control.

The electro-magnetic clutch shown here isn't really necessary - a simple slip clutch suffices.

A gallery of photos of the telescope is presented here for those looking for inspiration!

Recently I’ve added a digital finder scope, and ‘eFinder’. This is described here. It automatically improves GoTo accuracy to about 1 arc minute with respect to real sky RA & Dec.

I have decided that the current design no longer should be called a Dobsonian. It is so far from John Dobson’s original concept both mechanically and with the addition of tracking, GoTo and eFinder. It's an AltAz Scope!

© AstroKeith 2022