De-forking a Schmidt-Cassegrain Telescope

Interestingly, de-forking SCTs has been around as long as the SCT itself! The original owner’s manual for the 1970s vintage Celestron C8 describes how to do it and you could even buy a ‘tripod adapter’ for the C8. Nearly 50 years later the procedure is nearly the same. Briefly, you need to support the telescope so nothing falls as it comes apart. I place mine on a sturdy table covered with a towel. Start with the telescope on its base with the clutches loose. Before you start, gently scribe where the fork arm that has the dec clutch attaches to the base; this is so you can re-align this arm in case you ever re-fork the scope. On the LX200, remove the plastic cover from the bottom of the fork arm that has the dec clutch. This will give you access to the 4 bolts that hold the arm to the base. Using an Allen wrench slightly loosen these 4 bolts. You may need an extension to crack these bolts loose. Once cracked loose, snug them so the arm doesn’t move before you’re ready. Gently lean the telescope forward over the control panel and allow the telescope to pivot on the dec axis until the front of the scope and its dust cover are firmly supported on the table. Now loosen the 6 bolts (3 on each side) that hold the telescope to the fork trunnions. The middle bolt may be hard to reach and you may need to file down an Allen wrench to fit between the fork and the bolt head. Once all 6 bolts are loose, loosen the 4 bolts that hold the fork arm to the base by several turns; this will allow you to open the forks enough to slide it up and off the scope without scratching the tube. While supporting the forks to keep them from falling, carefully remove the 2 outer trunnion bolts from each side. Loosen the 3^rd until it is almost out. Once this 3^rd bolt comes out you’ll need to hold the mount to keep it from falling, so be careful! Carefully remove the 3^rd bolt from each side while supporting the forks and then lift the fork up and off the scope. Installation is the reverse of this procedure.

Very important! Do NOT put the trunnion bolts back in the scope! They may be long enough to bear on the mirror. Instead, place them in a labeled bag and store them with the mount. Purchase a set of shorter bolts from a hardware store to plug the holes on the telescope.

The first time you de-fork a Schmidt Cassegrain can be a bit tricky, but once you’ve seen how it is done it is fairly easy. However, please proceed with caution.