Anyone who has imaged with a SCT has probably experienced "Mirror Flop" when near the meridian, and possibly at other orientations. This is caused in part by the basic design of the mirror mount itself. In order for the SCT to be focused, the primary mirror must move closer or further from the secondary mirror by sliding on a baffle tube that directs the light to the back of the scope. The mirror is moved and held in place by only one connection, which is the focuser. This single support point can not keep the weight of the mirror from shifting as it moves across the sky. The tolerances between the mirror holder and the baffle tube are not small enough to prevent this "flop" or shift. My first attempt to halt mirror movement was done with long bolts to connect to the mirror cell holder as seen here: Mirror Locks. These worked somewhat, but I still got some movement when guiding, and adjustment to maintain collimation was very difficult. So, I made the decision to install the Software Bisque Locking Collar. The following is a brief pictorial of the process.
|When the wife is supportive, life is good :-). My operating location was the kitchen table.||The first piece out is the corrector. Remove the retaining ring and make note of the position of the cork spaces. Also note the position of the number on the corrector. Taking a picture is an easy way to return it to exactly the same orientation.|
|I had spacers at the top, bottom, and right side. I used masking tape to label the locations so each could be returned to its original position.||With the corrector removed, I carefully collected the spacers and taped and labeled them to a popsicle stick so they wouldn't get lost.|
|Here is the scope with the corrector removed . You can see the 3 markers for the spacer locations.||Next, I decided where the access holes needed to be cut and laid out the template on the scope with masking tape.|
|The Software Bisque collar installs over the mirror baffle tube. It needs a hole drilled in this tube as an "index" to keep the collar from rotating on the tube. A setscrew is tightened to hold the collar at this orientation.||The collar has now been placed on the tube. The indexing setscrew is the second one from the front.|
|I used a knockout hole punch to cut two very clean 1 3/16” access holes to allow me to reach the larger setscrews that tighten the collar on the tube. The tightening is done with a T-Handle allen wrench.||Two plastic plugs complete the surgery and all that's left is the reassembly. I also took this opportunity to clean my mirror, corrector on both sides, and inside of the OTA tube. I'm now ready to reinstall on my ParamountME and test the results.|