Cheap Electronic Focusing

I was recently asked a question on Astrobin about focusing, which got me thinking about posting something. Adding an electronic focuser to my rig definitely improved both the quality and frequency of my focusing. Focusing is acutely important for lunar/planetary work, and probably just as important (but easier) for deep sky astrophotography. I started out with a really terrible focuser on my old Meade department-store level scope, and thought I had hit the big time when I got a Crayford-style, dual-speed focuser on my Astrotech Imaging Newtonian. I've heard some people complain about the stock Astrotech focuser, but I guess I don't know any better and it is certainly way better than anything I had used before. After using it a while, I decided I wanted an electronic focuser. With my wobbly mount it is hard to focus by hand because the image jiggles all over the place whenever you touch the scope. I started shopping around and decided the Orion Accufocus was about the cheapest commercial setup that would do the job (you could put together a stepper motor and some gearing for less, but that started to look like too much bother to me). So I bought the Accufocus and started using it with the handcontrol/battery box supplied with it. I had to jerry-rig the attachment a bit, because the Accufocus is not designed for use with the stock Astrotech focuser. I attached the bracket that holds the stepper motor to the focuser via the two screws that set the focuser tension and locking; I replaced one of these screws with one that was a bit longer, on which I could thread nuts so I could independently attach the bracket and set the focuser tension. The pictures hopefully show what I did:

Although the handcontrol works fine, because the winters are cold in Utah pretty soon I decided I wanted USB control of the focuser so I could work on focusing from the warmth of my living room couch rather than sitting out in the snowy back yard. I picked up a FCUSB unit from Shoestring Astronomy. It works well with the Accufocus. Stark Labs has Mac-native software to run the FCUSB (called Shoestring Focus), and Shoestring provides Windows software. I started out with the Mac software, but after I started controlling my mount with PicGoto I had to run Windows anyway, and I found Shoestring's FocusPal works a little better than the Mac-native Stark program. So I now use FocusPal. FocusPal lets you run the focuser at variable speeds either as long as a button is pushed or in fixed-duration pulses. Typically I get the Moon or a bright star in my field of view and do rough focus with that. With stars, I use the diffraction pattern from my secondary mirror mount for rough focus; I just focus to get good spikes. Once I'm on my target, I pick a star with intermediate brightness and use the "fine focus" feature of Nebulosity, my imaging program, to get as good a focus as my patience allows. "Fine focus" provides two focusing metrics: intensity (which you want to maximize) and "half-flux radius" (essentially the size of the star, which you want to minimize). Both are shown graphically, so it is easy to see the effects of adjusting the focuser, even when the seeing is messing with your star.

So was it worth the cost of adding these upgrades? Yes! I get much better focus in much less time and stay warm while I'm doing it. I really couldn't use "fine focus" at all until I started doing electronic focusing. Now it is no problem to stop and refocus in the middle of an imaging run, and focus on my scope does drift a little (probably thermal expansion/contraction of my optical tube). Now I can correct for that.  There are, I'm aware, automated routines for focusing with these electronic focusers, but I haven't got any working yet.