Note: I discovered weeks after this test that the filter drawer of this lens actually contained a Nikon UV filter. That might have influenced the result, so further testing required.
Further testing the golden oldie 300mm F 2.8 AF Nikkor ED. At F4 with 56×180 seconds on ISO800, Nikon D750, HEQ5 and the Lacerta MGEN II autoguider. A lot a gradients to remove, and really bad conditions with fog, cirrus, passing contrials, in general a sky not over SQM 19.50
There is something wrong with the starshape in this image. The colors are ok and the nebulosity really stands out. However, zooming in reveals strange artefacts.
I checked the light frames and decided to delete 30 out of 56 lights, because the focus was not ok. In addition I removed some lights that were really off track, had very bad star shapes. Futhermore, were before AstroPixelProcessor refused to register the frames, it now did register and stack the frames. Obviously only half of what I had before. So I lost a lot of nebulosity and nuance in the image!
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.
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