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I'd never given much thought to using Autofocus partly because of the cost of such kit, and partly because I didn't know just how useful they would be. After all I use a Bahtinov mask for focusing so it can't be that bad can it??
Then I started using filters and wanted to take photos with and without filters. Having to refocus proved to be a bit of a pain, so I started looking at focusing systems and especially the DIY variety. I had a stepper motor from an old printer and an Arduino board so what else did I need. Well try a stepper motor driver? Easy enough to get one of those and the code came from the Source Forge repository of Robert Brown.
After some fiddling around and trying to get things to work I finally had a box with the electronics in it and a motor all wired up to use with it. I also moved from the Arduino Uno R3 to a clone of the Arduino Nano.
I shan't list the components or give details of the code as this can all be found on Robert Brown's repository.
This is the breadboard version of the electronics. This showed a catch with using a recycled stepper motor and underlines the importance of knowing which leads are which. For a while the motor would not turn properly and after taking a meter to the leads to determine which lead went to which coil I swapped the two middle leads and hey presto the motor ran perfectly.
I have built the minimal version and omitted the voltage regulator as I will be powering the Nano clone from USB.
Having tested the electronics and ironed out the wrinkles, time came to put it all together on stripboard, then design a box layout.
Heat shrink on all exposed connections, and connectors mounted on the board to connect up the flying leads made installing the board a breeze.
The focus motor mounted on the focuser.
The mount was made from aluminium strip.
A tip for potential builders, remove the locking screw on the focuser or slacken it right off. I found adjustment of the tension screw also helped. If this is too tight the motor will struggle to turn properly or not turn at all.
Test shot after a bit of trial and error.
Mu Cephei, Erakis, or HD 206936, also known as the Garnet Star because of its red colour, not so obvious in this image.
Settings needed looking at for autofocus to work but once this had been done I shot NGC281 and was happy with the result.
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