How to Convert your Sky-Watcher 8x50 Finder into a Guide Scope

Many Sky-Watcher telescopes come with a decent quality 8x50 finder scope. I converted my scope into a guide scope for use with a ZWO ASI 120mm Mini.

The telescope I use for backyard astronomy and astrophotography is a Sky-Watcher EvoStar 100ED. It came with an 8x50 right angle finder scope (8x magnification with an aperture of 50mm). Since this is roughly the size of the average guidescope, I thought I could convert this to one. There are many people who have done this and there are plenty of posts about it in forums such as CloudyNights. Most people use this adapter to connect their camera to the scope. I thought I could save money and have it 3D printed instead.

I’m not much of an expert in CAD so I looked on Thingiverse to see if I could find an STL file of the adapter. I found this part and thought it looked promising. Some quick searches revealed that the Datyson was similar to the ZWO 120mm Mini camera I own, so I had it printed from a local 3D printing shop for $5. Below on the left is the 3D printed part.

The part threaded well into the Sky-Watcher finder, but didn’t fit properly into the 1.25" thread on the camera. So I had to improvise. The 120mm Mini came with a 1.25" to C thread adapter. I simply took this adapter and super glued the female C thread side to the 1.25" side on the 3D printed adapter.

Unfortunately I hit one more snag. As I tested the camera and new guide scope on random objects in my room, I was unable to achieve focus. Turns out the camera was too close to the objective lens of the finder scope. In order to solve this issue, I used a junk Celestron 1.25" T adapter I had lying around. I unscrewed the silver extension bit and T adapter, and was able to thread in the camera from one end. In the other end, I slid in the guide scope with the 3D printed adapter + superglued C adapter + 1.25" extension tube that came with the ZWO camera. See the full assembly below.

This solution was put together with things lying around my house, but overall the connection from the guide scope to the camera is very sturdy. I plugged my new guide scope into my computer, switched on Sharpcap, and the whole thing worked well. Here’s a screenshot of Sharpcap as I pointed the scope to a trophy in my room.

I had to do a lot of googling to find the right 3D printable adapter, as well as to determine whether the 8x50 finder would even work at all as a guide scope. I hope this post has helped to inform you that it is possible to convert your 8x50 finder into a guide scope, and that it works well! Some improvisation may be necessary to achieve correct focus, but that’s all part of the fun. Clear skies!