How to electrically drive manual camera lens?

[michaelmorris]

I recently purchased a Pentax Takumar 200mm lens for astrophotography with my Canon DSLR.  I'm really pleased with the lens, but I miss having the ability to drive the focus remotely.  One idea would be to somehow drive the focus ring with a Skywatcher/Orion autofocus motor (I have two, and it wouldn't take long to remount one).  Does anyone know of any examples of how this (or a similar solution) has been executed?

Thanks

[Scott]

I'm sure I've seen something similar in the diy section but can't seem to find it. Kind of like a motor driving the focuser with a friction wheel. Sorry, not much help hey.

[Stu]

I know Gina was doing this with camera lenses on a widefield rig at one point, not sure if she completed it or not. Will try to find it

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[Stu]

I think this may be it...

http://stargazerslounge.com/index.php?/topic/177070-Arduino-controlled-focussing

Stu

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[Photosbykev]

There are a number of motorised solutions that are used mainly by the timelapsing and video crowd. They typically use a belt drive around the lens on the drive motor or mount a gear around the lens and use the drive motor that way. Obviously the motor hardware needs to mounted and again look at the DSLR video options, they use a pair of aluminium rods mounted off of a the baseplate extended forward under the lens.

[davew]

Here was my solution. It was easier than it may look to set up. Uses a SW focus motor and belt drive.

Dave

[michaelmorris]

Thanks' that's pretty much what I'm planning. What pulley and belt did you use?

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[davew]

Hi Michael,

The pulley is a 24 tooth 6mm bore from Motionco. No matter what you want to use, with a SW motor, the shaft is 6mm according to my Motionco receipt. Serial number PL3M024AL.

The belt is a 9mm rubber timing belt from the same company.

The length of belt can either be worked out by clever maths or a piece of string like I did it !!

Dave.

My latest project will be a Lakeside motor from Ian King. I have the strangest feeling it will cost 5 times as much for pretty much the same result !

[davew]

Oh, another thing .........

If you go the SW motor route, I found that 9v is way too much voltage. The motor goes wild with so little resistance. 6V is closer and 3V is useless. I use 4.8 volts that's provided by 4 rechargeable AA batteries...... Perfect.

Dave.

[michaelmorris]

Hi Michael,

The pulley is a 24 tooth 6mm bore from Motionco. No matter what you want to use, with a SW motor, the shaft is 6mm according to my Motionco receipt. Serial number PL3M024AL.

The belt is a 9mm rubber timing belt from the same company.

The length of belt can either be worked out by clever maths or a piece of string like I did it !!

Dave.

My latest project will be a Lakeside motor from Ian King. I have the strangest feeling it will cost 5 times as much for pretty much the same result !

Cheers

I too was looking at MotionCo.  Based on your set up, I'm minded to go for the 108 tooth (30cm) 9mm wide HTD belt and the 15 toothed HTD pulley.  My rationale is that few teeth on the pulley > slower (more accurate) focussing - is this reasoning correct?.  I guess the down side will be less torque due to the fewer number of teeth on the wheel that are in contact with the pulley.  Does this sound reasonable?

[ChrisLX200]

Cheers

I too was looking at MotionCo.  Based on your set up, I'm minded to go for the 108 tooth (30cm) 9mm wide HTD belt and the 15 toothed HTD pulley.  My rationale is that few teeth on the pulley > slower (more accurate) focussing - is this reasoning correct?.  I guess the down side will be less torque due to the fewer number of teeth on the wheel that are in contact with the pulley.  Does this sound reasonable?

You won't need any torque for this job, resistance will be close to zero anyway. You do need (preferably) a geared stepper motor though.

ChrisH

[michaelmorris]

I need to keep this both simple and cheap, so using my existing Skywatcher Accufocuser is a prerequisite.

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[davew]

Sorry for the delay getting back.

It's true that a smaller drive wheel will give less movement to the lens but I've never found it a problem after my voltage fix. All lenses seem to be ok even though the range of operation is so different. Some modern AF lenses hardly move from close up to infinity and some lenses need winding round quite a bit. The slow movement provided by 4.8 volts and on the slow setting on the control box seems to sort it all for me. I made myself an extension lead so I didn't stand at the mount to focus.

Any further questions just give me a shout,

Dave.

[michaelmorris]

Parts ordered.

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[michaelmorris]

Focussing rig now complete.

See thread in DIY section for more details.

http://stargazerslounge.com/topic/221121-diy-electronic-focus-control-of-manual-dslr-lens/#entry2377304

Thanks everyone for your help with this.

[davew]

That looks a very well thought out system.

All I would say is don't tension the belt too much. It will try and pull the camera / lens over and if it fails to do that, pull sideways on the focus mechanism.

I have to say I'm impressed.

Dave.

[michaelmorris]

That looks a very well thought out system.

All I would say is don't tension the belt too much. It will try and pull the camera / lens over and if it fails to do that, pull sideways on the focus mechanism.

I have to say I'm impressed.

Dave.

Thanks. The lens has a very positive manual focus (i.e. much stiffer than on an autofocus lens set to manual). It therefore requires a bit of tension in the belt, else the belt slips.