Homemade DIY focuser for telescope with computer control

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.

The old evil focuser and motor. New jobby is 400g lighter.

Several of my Recent Images have been focused with this system.

G182.4+4.3 Supernova Remnant
G156.2+5.7 Supernova Remnant
IC443 Jellyfish Nebula SH-248
CTA1 G119.5+10.2 Supernova Remnant
SH-284 Sharpless 284, Do25, Do 23
SH-232 Sharpless sh-232, sh-231, sh-233, sh-235
SH2-217 Sharpless 217
NGC2174 Monkey Head Nebula, Sharpless 252, Sh2-252
SH2-282 Sharpless 282 Sh-282 Sh2-282
NGC1491 Sharpless Sh2-206
HDW3 Hartl-Dengel-Weinberger 3 PN G149.4-09.2
SH-263 Sharpless 263
IC410 Sharpless 236, NGC1893
SH-198 Sharpless 198, Soul Nebula, IC1848
SH2-212 Sharpless 212, NGC 1624
B33 Horsehead Nebula
SH2-210 Sharpless 210
SH2-200 Sharpless 200
IC63 IC59 gamma Cas nebula
SH2-187 Sharpless 187
NGC281 IC11, Sharpless Sh2-184, Pacman Nebula
SH2-176 Sharpless 176
NGC281 IC11, Sharpless Sh2-184, Pacman Nebula
SH2-173 SH2-173 Phantom of the Opera LBN 593
SH2-69 Sharpless 69, LBN 99
SH2-155 Cave Nebuka, Caldwell 9
NGC7635 Bubble nebula    Sh2-162
SH2-140 Sharpless 140
SH2-101 Sharpless 101 Tulip Nebula
NGC6888 Crescent nebula Sh2-105
M51 Whirlpool galaxy
SH2-224 Supernova Remnant
NGC7293 Helix nebula
IC1805 Heart Nebula
SH2-170 Sharpless 170
CTB1 Supernova remnant
SH2-168 Sharpless HII regions. Sh2-169 and Sh2-168
NGC7380 Wizard Nebula Sh2-142
PN G75.5+1 Soap Bubble Nebula
IC5146 Cocoon Nebula, Caldwell 19, Sh 2-125
M16 Eagle nebula NGC 6611 sh2-49