My oldest telescope Meade ETX-125 focuser modification project (published a decade ago on Instructables):
In addition to improving the smoothness of the focuser motion, this mod allows setting the scope into a perfect focus by dialing a value from the list of settings for each of my eyepieces and camera backs. That's also helpful for arranging exposures with the rear mounted camera while tuning the perfect focal position from test shots' analysis. See it in full details on the Instructables website.
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