Astro-Physics 900 GTO Mount
After using an Orion Atlas EQ6 mount for the first year and a half with my AP160 EDF I found a nice used AP900 GTO mount for sale on Astromart for only $6000. Buying it used I was able to save over $2000. Unlike the Astro-Physics refractors that go up in value over time, their mounts depreciate slightly. This is largely because thanks to Astro-Physics ramped up production, they are much better able to keep up with demand.
Like all things Astro-Physics, the AP900 GTO mount is a work of art. The mount head weighs the same (54 lbs) as my old Orion Atlas mount, but can easily hold twice the weight with about 10 times the precision and a huge improvement in stability. Below is a test I ran of my AP900 mount showing a very smooth periodic error. This is without periodic error correction. (Click here to compare to my old Orion Atlas.)
Achieving precise polar alignment is fairly easy with the AP900 thanks to its tight tolerances and precision machining. I typically get very close alignment using the AP polar scope alone. Then using WCS polar alignment software I dial in near perfection in 15 to 20 minutes. It has takeen some practice to be able to get reliable and repeatable near perfect polar alignment, but I have it down to a science now and can typically be right on the money before astronomical darkness has even set in.
Thanks to the AP900's excellent tracking and stability my imaging has improved significantly since getting this mount.