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My old astronomy project:
An idea how to build a motor focus


Motor focus with stepper motor

  1. Mechanical parts
  2. Worm gear
  3. Stepper motor
  4. Conclusion

1: Mechanical parts

Parts from old M42 lens

It's very hard to focus a telescope, you can't touch the telescope because it will get it to vibrate. And very small adjustment is necessary.

Here is some early planes how to get rid of this problems:
I going to build a motor focuser (at least give it a try). It will be placed between telescope/lens and camera as a fine adjustment unit.

It's complicated because of the small distance between camera and lens (for a telescope it's not that critical). 32mm is what I have to fit it in. I use an old wide (28mm) angle lens which I will rebuild for this purpose. The selected lens can reach a adjustable focus range of 6mm and it's very mechanically stable.

I also take parts from a macro extender to get the Pentax M42 thread. It's planned to have Pentax M42 thread at both end but also have an ocular 1 1/4" holder.

How to connect the motor and gearbox I don't exactly know yet, it's not so much space for this.

Now a lot of mechanical work have to be done.

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2: Worm gear

Wormgear

Now the first parts are finished, the white ring is a one part of the worm gear, home made and treaded with M5. Now made of plastic, maybe I have to replace it with one made of aluminum in the future. At least I now know it's possibly to make such gears.

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3: Stepper motor

Stepper motor with wormgear

Mounted together, the most left part is a 2x tele extender. Now the tricky part is left how to connect the stepper motor to the worm gear and also to build some electronic stuff to drive the motor.

This motor comes from a 5 1/4" floppy drive and it's a little to big and heavy, maybe I can find a smaller one. The motor could also be replaced with a DC-motor which is much easier to control.

One turn of the worm gear will move focus about 10 um.

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4: Conclusion

First test show that it works fine, very easy to control the focus (manually).

Today replaced with a more modern construction.

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