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Having the Right Gear (Ratio)

The “old dog” Takahashi needed autofocus and I did it the standard way- by attaching an already geared down electronic focuser motor directly to the focuser shaft. Here’s a pic of my original attempt with the focuser on the left side of the OTA (Optical Tube Assembly:

The problem I had was that this beautiful old telescope has a MASSIVE focuser and this motor simply wasn’t strong enough to lift it plus a camera when the scope is pointed straight up at the zenith. Fortunately on the other side of the focuser is a fine focus knob. To put it simply it’s a geared down focus control that I added a few years ago to get precision focus by hand. I pulled off the fine focus knob to access the shaft. I connected the motor to this to get a beneficial gear 7X reduction. I could no longer use a highway cruising gear to climb a mountain!

Here is the focus motor mounted on the fine focus (MEF4) shaft of my Takahashi FSQ106N. You almost can’t see the focuser moving!

As expected the autofocus routine takes longer than normal however the result is nice, sharp stars!


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