Paramount ME II Classic

See the Paramount Limited Warranty page for details about what's covered.

On-axis Absolute Encoders vs. Motor-based Encoders.

Paramount's equipped with on-axis absolute encoders know where they are at all times.  Paramount's with incremental encoders (or motor-based encoders) know only how far they have moved since they were initialized using a nightly process called homing.

The crucial additional difference is that the on-axis absolute encoders are fitted directly to the mount axes themselves, bypassing the worm drives.  Paramount's with incremental encoders are fitted to the worms instead, which means that with incremental encoders alone, periodic errors in the worm drive show up in the tracking.  These mounts must be calibrated and corrected using a process called periodic error correction (PEC), which measures and records the repeatable gear train errors and removes them.  (TheSky features advanced, multi-harmonic PE detection and PEC calibration that minimizes periodic error in mounts with incremental encoders.)

For mounts with incremental encoders, homing re-zeros the encoders when precise sensors on each of the axes are reached. From then on, the incremental encoders are in effect delivering absolute readings.

However, the crucial additional difference remains, namely that the incremental encoder system is behind the worm drive, and periodic error correction is still required to get the best out of the RA tracking.

High-resolution on-axis absolute encoder technology is significantly more expensive than incremental encoders.

The short answer is, “it depends.”

On-axis absolute encoders eliminate periodic error and enable the mount to always know where “home” is.

That’s convenient and expedites setup for an evening of imaging. However, with Paramounts, periodic error is already very low, and after a one-time training, it becomes negligible. Moreover, Paramount’s included Homing software homes in only 15 to 60 seconds.

So, at least with Paramounts, periodic error is practically non-existent and homing is a breeze.

What about pointing and tracking?

Without encoders, Paramounts routinely allow 5-to-10-minute unguided exposures; many have reported 20 minutes. Also without encoders, Paramount’s produce all sky pointing accuracies at or below 30 arcseconds RMS.

Absent Paramount’s exceptional software, that performance would not be possible. Operating in conjunction with TPoint™, ProTrack™ continuously updates the mount’s position across both axes to correct system-wide tracking errors including tube flexures, atmospheric refraction, polar misalignment, harmonic errors from mis-centered encoders and/or worm gears, and more.

On-axis absolute encoders alone cannot correct these errors which exist with all telescopes. A properly applied telescope model is necessary to achieve superior pointing and tracking.

So are on-axis absolute encoders right for you?

Perhaps if you want to enjoy the conveniences mentioned above. And for many, that’s enough.

With that said, the optional on-axis 26-bit Renishaw absolute encoders with 0.02 arc second precision are the finest available and they operate in temps as low as –40° C.

See the Paramount Lubrication Video for details how to lubricate gear-driven Paramount mounts.  (Log in required.)