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).


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.

NGC4565 in Coma Berenices

And what a beautiful edge-on sprial galaxy this is! I made almost 3 hrs of 120-second frames with the ASI183mm Pro and the Esprit. Then I combined the resulting monochrome (Black/White) image with the older C11/Nikon D750 color frames I had from last year. This process included debayering of the color frames into a Red, Green and Blue version. And again recombining an LRGB with the monochrome and RGB frames. Finishing in APP (Background neutralisation, removing Lightpollution ) and in Photoshop.

This is the monochrome ASI image. It is wortwhile exploring it a full resolution in Astrobin, detecting the many little galaxies in the background.

Since the Field of View of the Esprit/ASI is much larger then the C11/Nikon, this image was cropped to fit the color frames.

M106 added more data

I could add 116 shots of 120 seconds, in an attempt to bring out the outer spiral arms more clear. The total integration time is now over 8 hours and this is the LRGB combination below (all shot from Meldert, Belgium). Click on the picture to go to Astrobin.

These 4 nights were more or less used, there was some high-altitude clouds passing by which not always affect the photometer (click for a larger image)