I hate focusing. Or rather, I hated it. My newtonian telescope, like most others, came fitted with a nasty rack and pinion focuser. These have slop as you change direction, you can't do fine adjustments, they weigh a ton, and can flex alarmingly over time. We all know the problems with focusing. You reach a point where the picture doesn't seem to change much, so you never know where the very sweetest spot in the focus is. This focuser (see pic at bottom) was motorised by me several years ago, but the motorised system didn't give me very fine control, and the motor running at fast speed tended to make the Artemis camera crash.
So I decided to make my own, using my normal "blunder in naively and see what happens" approach to making things. The basic points I wanted to cover:
What did I end up with? Well, it sort of looks like a focuser.. See pictures below. I don't *do* pretty. I only do functional. A decent machinest will do a far better job, but, there is always a lot more pleasure to be gained per astrophoto when you make bits yourself. More commercial crayford focusers are of a more enclosed form, whereas mine is more "open frame" approach. I do have another tube that can be used around the drawtube, but it doesn't really add anything. Inside the OTA is a ring of tightly fitting flocking paper that prevents any light getting in around the drawtube. The silly colours are mainly due to me experimenting with various clothes dyes in the anodising.
To interface with the computer, I have used the Artemis Focuser module from Steve, Arthur and Co. This consists of a small black box of electronics. This unit takes signals from your computer and drives the stepper motor on the focuser. The kit just contains the electronics - it is up to the user to find a stepper motor and attach it to their own telescope focuser. It interfaces to the computer via USB and comes with an ASCOM driver.
This means I can use FocusMax to do the focusing. This software creates a model of your telescope by measuring out of focus star sizes at various points. When you want to focus, you just open the program and press focus. It take automatic control of the CCD camera and focuser, and dances around magically on the screen, arriving at perfect focus within about 30s to 3 minutes depending on where you started from.
I sourced my own Stepper motor and 1:150 reduction gearbox from RS, who are just up the road. Part numbers 351-4574 and 336-422. The ARtemis module came in a kit form... actually just two circuit boards... one of which I had to source the parts, build and box myself. Having an RS trade counter 2 miles away is such a luxury! The Artemis module works extremely well, and is to be strongly recommended.
Overall, I'm very happy with the outcome of this project - focusing is now a joy. It takes the unknown out of focusing, and is easy to re-focus between filters, or refocus several times during a long exposure run as the world cools down.
You need a drawtube of course. Bore out some 2.5 inch bar and mill a flat down the side making sure it is lined up. The flat wants to be running parallel to the long axis of the tube. The part is very strong! Finally it was etched in caustic soda, and anodised matt black.
And a couple of upright bearing blocks. These are mounted 120 degrees apart and use 4 inexpensive bearings to support the tube.
You need some purple bits
Along with some silver bits
And a flat thing to put it all on
Put it all together
And bolt to scope
and hope it doesn't fall off
Fire up focusmax, and shoot some images!
A short Video 5MB showing it working.
Several of my Recent Images have been focused with this system.