DIY Electric Focuser For Celestron 127 SLT Maksutov/Cassegrain

Interested in planetary and lunar photography with your telescope? You might find my article on astrophotography with Alt-Az scopes interesting too.

One of the tradeoffs with the mid-price Celestron 127SLT is that it shakes rather badly when you touch it, and takes several seconds to settle down. I’m focusing using a Bahtinov mask and Sharpcap’s Bahtinov aid, which gives a numeric indication of the accuracy of your focus. It can be a slow process to focus it since you tweak, wait, and tweak again.

I decided that a remotely controlled electric focuser would allow me to do a much finer focus than I could achieve by hand, since it would not require touching the scope.

This design doesn’t require removal of the focuser knob — only the rubber sleeve that covers it. This sleeve slips off by hand.

If you do pursue a different design that requires removal of the focuser knob, be warned that you must not tip the telescope down toward the table with the focuser knob removed — the knob is all that prevents the main mirror from falling forward and smacking into the corrector lens, which requires a teardown and cleaning to fix. This design does not risk that situation.

It took some head scratching to figure out how to mount the motor to the optical…