Re: Tracking and guiding with and without encoders - Part2

Roland Christen

You will notice improvement with long focal lengths in good seeing. Otherwise you are limited by pixel resolution and atmospheric seeing.

Using the 180F9 refractor I was getting 1.2 to 1.3 arc sec FWHM all night during good seeing. The mount was guiding in both axes at 0.1 to 0.13 rms. I don't think that this would be possible with the non-encoder version of this mount - the Mach1. In our Chile observatory (1600 encoder mount) at LasCampanas we measured FWHM of 0.9 arc sec with the 305F8 Mak-Cass astrograph when we were setting it up.

As I indicated before, the Mach2 doesn't really work without the axis shaft encoders, just like your mount doesn't really work without the motor shaft encoders. Every decent mount has to have encoders somewhere, either on the motor shaft or on the axis shaft. The feedback from these encoders provides loop control and steady tracking rates. If the encoder is on the motor shaft then it does not account for errors in the geartrain. If it's on the output shaft then all errors are accounted for except for the encoder itself. Since we are opting to use high accuracy encoders on the output shaft, the errors are very very small, almost 5 times smaller than the best you can do with worm and spur gear reduction, even accounting for the use of PEM. You are then only limited by the atmosphere and your scope/camera resolution.

The encoders also provide a number of other benefits that people have wanted all along, so we are advancing the technology and raising the bar. The Mach2 is a very effective mount for high performing scopes and can handle larger loads better than its predecessor.


-----Original Message-----
From: badgerz49@... [ap-gto]
To: ap-gto
Sent: Tue, Sep 17, 2019 11:34 am
Subject: Re: [ap-gto] Re: Tracking and guiding with and without encoders - Part2

Roland - so you are saying Total RMS will improve with encoders.  Back to the original question; how much improvement is there in Total RMS for guided imaging with typical 2-3 second guide intervals?

In limited testing I haven't noticed any improvement in Total RMS with PEC on vs. off, which is why I have doubts encoders will improve Total RMS much, if any.  That's with an excellent PEC curve that almost eliminated PE.  Seeing seems to be the limiting factor.  Fast oscillations, backlash, and PE are negligible.


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