Adding a fine focuser to a 4" Mak

The Sky-Watcher Mak's built in focuser is surprisingly good for a budget compound telescope, but there is still a slight image shift when reversing direction during focusing. It's also quite tricky to get the focus just right when doing astro photography. Having read that the Sky-Watcher Maks have a 36.4mm threaded eyepiece holder that is compatible with some high quality Japanese equipment, I decided to try out a Borg helical focuser.

The first picture shows the 1.25" eyepiece holder as supplied with the telescope. At the top is a 45mm diameter knurled ring that screws onto the port at the rear of the telescope. Less easy to see is the 36.4mm threaded retaining ring that attaches the knurled ring to the eyepiece holder.

Original eyepiece holder Dismantled eyepiece holder

I was able to unscrew the retaining ring by securing the eyepiece holder in a "workmate" style vice, then using a hammer and punch gently to loosen it. The two small holes in the ring provide just enough purchase for a sharp punch. (A better method is to use two pieces of stiff wire, such as nails with their points filed down, clamped in a vice to form a crude pin spanner.) The parts weren't glued together, but there was some of the infamous sticky Chinese grease on the threads. The second picture shows the three parts of the disassembled eyepiece holder.

The Borg #7315 helical focuser is shown in the next two pictures. First is the focuser as supplied, and secondly with the Sky-Watcher knurled ring and retainer fitted. Note that the focuser's travel is restricted by the knurled ring so the last 2mm of travel is lost.

Borg #7315 helical focuser Borg focuser with Sky-Watcher knurled ring

Lastly, here's the rear end of my Mak with the newly fitted Borg focuser. Since buying the Borg focuser I've invested in some other accessories with compatible threads. I now have the beginnings of a modular telescope system.

Sky-Watcher Mak with Borg focuser