Although the DF-2 focusser comes with a T-threaded adapter that fits most SCT's a conflict between the focussing motor and a raised edge on the SCT prevents the two from making proper contact.
The solution to this problem is to make an adapter which is just a thicker version of the standard DF-2 adapter, i.e. one that has a v-grooved edge on one side and a female T-thread on the other. I had mine made out of bronze instead of aluminum to avoid the risc of thread locking (same-material thread pairs can sometimes fuse together). Since bronze is quite heavy I included a series of holes along the circumference, thereby reducing the total mass of the adapter by nearly a third:
The inside of the adapter is threaded and painted black to minimize stray light. In the pictures below it has been screwed onto my 8" Meade LX100 and the DF-2 is ready to be mounted:
The AO7 guider requires a male T-thread for mating to the telescope, so I designed a T-threaded adapter for this purpose:
As indicated by the arrow the adapter has a small hole on the side so that I can insert a key and gain leverage in case it gets too tightly screwed in. The other adapter also has such a hole on the side. Again, the inside is threaded and painted black to minimize stray light. Once screwed into the DF-2 the assembly is ready to accept the AO7 - or anything else which is designed to mate with the basic SCT T-thread:
In the picture above a Celestron f/6.3 focal reducer has also been inserted between the DF-2 focusser and the AO7. Note that use of such a focal reducer only will work for the small-chip ST7, for the larger chips found in ST8 and ST10 the off-axis abberations become too large. If you want to use a focal reducer with these cameras and the AO7, then go here to see how an Astro-Physics 0.67x reducer can do the job.
This arrangement is quite stable and the DF-2 can easily handle the load of the AO7/camera. However, for proper balancing of the
SCT in declination a counterweight should be added to the opposite side of the scope. I can also use filters with the
configuration above, since I have a special way of mounting filters within the AO7 that avoids the
need for a filter wheel.
Here's my mechanical mating page where you can see more examples of custom made adapters.
Comments greatly appreciated! (mikael@leif.org)