Using the PegasusAstro FocusCube 2 on an Esprit APO 120mm

There are good reasons to switch the a motor controlled focusser:

  • automating sequences in Sequence Generator Pro
  • Autofocus
  • Automated focussing after a filter wheel switch
  • Getting comfy inside while able to fully control your telescope
  • Go to sleep while your equipment takes care of image acquisition
  • no more slipping of the focusser with heavier loads

Why the PegasusAstro focuscube? I actually ordered the Lacerta motofocus first, however there were delivery problems. It first took two months to deliver, after which nothing happened. On inquiry I learned that it would take another two months. I decided to change to the PegasusAstro, and a few days later it was on my telescope, mounted and working…

Both these brands could demonstrate that the motors would actually fit on an 120mm Esprit. That was my main reason, other considerations were the strict requirements of connecting to a PC, working with SGP and similar software, and the ability of attaching a handbox. The PegasusAstro FocusCube was standard delivered with a temperature sensor (option with the Lacerta).

Picture: PegasusAstro.com

It was not difficult fitting the FousCube to the Esprit standard focusser. The only challenge was to shift the L-frame so that the two bolts could fit the focusser body, while a the the same time the axis and the connecting cylinder were also aligned. The two screws were part of the assembly of fixation material delivered with the FocusCube. They fit the smaller screws of the Esprit focusser.

The two bolts fit the smaller sets of predrilled holes, which have tiny little hex screws inside. They are easily removed and replaced with two bolts that are part of the material send along the FocusCube.
The FocusCube attached to the Esprit standard focusser.

Getting autofocus working with Sequence Generator Pro, and the FocusCube was also a matter of trial and error. After two nights the autofocus works very well.

This is the full set of settings that work with my equipment:

  • when you cannot get a nice ‘V’-curve when autofocus runs, try to increase the exposure time. The image statistics should give you at least 50 stars. Below that value, the HFR values become erratic and unreliable. I use 20 seconds for a 7 nm H-Alfa filter.
  • remember that autofocus is intended for small corrections, so you should already be near focus before you can run it
  • always run autofocus before a filter switch. In theory the filters are parfocal, however in practice they rarely are
  • I only run autofocus per degree Celsius. If the temperature doesn’t change, there is little reason for focus. The whole autofocus process takes time, maybe 5 minutes or so, time that you loose imaging.
This is an actual screenshot of my first run with autofocus, based on the above settings.