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One thing I noticed with the 77ED was that at least one of the colours in an RGB run would be slightly out of focus, I noticed this on a few images and checked it all with a bahtinov mask. Going between RGB and having to change focus all night is not something that can really be done manually. There is also the problem of compensating for temperature changes over the course of a night. Focusing is the last part of my workflow that is not automated, so it was time to build a full auto focus system.

Accurate auto focusing is not really possible with the helical focuser that original came with the 77ED, so the first step was the upgrade this to the M57 Feathertouch. I’ve always had difficulty with heavy imaging trains and 2″ eyepiece holders, I’ve never found them to be very reliable and can introduce tilt quite easily. The M57 version of the Feathertouch allows the Borg adaptors to screw directly in making it all rock solid. I added in a camera rotator as well, it won’t really work without this as it locks your CCD angle in wherever the threads tighten up.

I then noticed a great thread on Stargazers Lounge by Neil Chase, who had also started his own automation group (SGL Observatory Automation). The idea was to use a combination of Arduino and Motor Driver to build an ASCOM compliant Motor Focuser. The programming side was really straightforward, it just took a wee bit of tweaking some of the variables to match what I was doing. The Feathertouch doesn’t have any fixing points so it took a bit of trial and error and a few bits and pieces from eBay to properly mount a stepper motor on it’s own frame bolted onto the main section of the scope. The result works quite well on a artificial star, now to just get it working with AquireStar to automatically find focus stars during imaging runs.


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