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The 'EC' suffix is the one with an encoder on the RA axis. The CEM120EC2 has one on Dec too but that doesn't help for unguided imaging and it's not a portable mount.
I use my CEM25EC for unguided imaging. I've tested it with 2000mm and don't see any RA movement. However, the encoders only eliminate the RA periodic error and that only serves to highlight the next greatest error source which manifests as polar alignment error. That might be due to the initial setup (Polemaster is 30 arc-sec/pixel) or it might be due to external issues like a tripod leg settling into the soil. That level of error shows over 10 minutes @ 2000mm and would be negated by guiding.
I have no complaints and enjoy the simplicity but I'm under no illusion that a portable unguided setup will be the equivalent of a guided system.
The common expectation seems to be that they should be the same and when they aren't, it's considered a failure of the mount and that's just unrealistic.
Steve.
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