DIY electronic focus control of manual DSLR lens

[michaelmorris]

A few weeks ago I decided to investigate adding an electric focussing capability to my newly-acquired SMC Pentax Takumar 200mm lens.  It’s a great lens, but having to manually get focus has proven to be a tricky and on at least one occasion the focus has slipped.    After doing a little research and looking in my wallet, I decided to try to adapt my existing Skywatcher Accufocus controller. 

http://stargazerslounge.com/topic/219776-how-to-electrically-drive-manual-camera-lens/

This way I could control the focus either through the Skywatcher focus control box or via my PC using my Hitecastro DC Focus Controller.  I wanted a small, lightweight rig to hold the Accufocus so that I could still use the DSLR and lens on a ball head. 

The rig is made up of some spare 2mm thick aluminium strip I had left over from a previous job bolted into an L-shaped bracket.  This attaches to the base of the camera via a Manfrotto quick release shoe.  I had to remove the rubber pad from shoe and grid out one edge and the base of the shoe to accommodate the aluminium strip.    

I added a short right-angled piece on the back of the bracket to brace against the back of the camera to stop the bracket from rotating.  Both this and the base of the bracket were padded with some strips of rubber from an old mouse mat superglued to them.

The Accufocus drives the focus ring via a toothed pulley (Aluminium 3mm HTD Pulley, 15T 6mm Bore) and a matching rubber timing belt (HTD 108T, 9mm wide length 324mm) from MotionCo.

http://www.motionco.co.uk/pulleys-belts-c-25.html

In the end, I found the best (and by far the cheapest) way of getting the timing belt to grip the focussing ring of the lens was simply by putting some rubber bands around the focussing ring.

In use, if I set the Accufocus motor to its slowest setting, it will allow me to achieve critical focus and will hold it there.  The bracket does flex a little when driving the driving the focus ring, creating a form of backlash, so autofocussing using this rig could be problematic.   However, using thicker aluminium would have meant I couldn't got the bolt on the hot shoe to screw on to the base of the camera.

[Mav359]

mmmm i like that

[Luis Campos]

Indeed!

What a great idea

Cheers,

Luís

[Gina]

Yes, looks good   A couple of differences from my arrangement.  I used an inside out belt on the camera lens to engage the timing belt and stepper motors rather than a DC motor.

Now I'm thinking of other drive methods when I get back to producing a wide field rig again.