Quote:
Originally Posted by Wavytone
Adrian I have the 311k encoders on my AZ8, thats 4 arc sec per step. They are quite simply a game-changer.
Admittedly there a few unknowns - the mechanical errors in the mount (the axes wont be precisely perpendicular), plus the effects of flexure in the tripod, mount and scope. The latter are significant in dobs as well as cheap metal mounts like the EQ5/EQ6. The other unknown at this level of accuracy is atmospheric refraction and so far I do not know whether SkySafari or the Nexus DSC are compensating for this. Maybe, maybe not. So far I've only had it out a few nights and not long enough to really test these aspects but what I do know is that it does reliably locate objects to better than 10 arc minutes with the AZ8. And it will do this all night from the initial calibration. No resetting, no recalibration required.
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Another critical underlying factor is the construction quality of the encoder itself. Not only do errors in the construction quality of the mount and telescope come in to play, as the encoder resolution increases, the construction quality and mechanical alignment accuracy of the encoder disc and shifts within the encoder housing becomes critical. At the price point of these mega resolution magnetic encoders used on amateur telescopes (very cheap ); it's highly likely that radial and axial alignment errors and concentricity errors of the encoder disc itself will offset any gains that may have been achieved by any additional rotational resolution gains of the encoder itself. Mechanical alignment errors of a few microns even will swamp any gains by the extra rotational resolution of the encoder itself. To the extent in fact that its quite possible that in the field a high quality 10k or 32k encoder might outperform some cheaper > 100k encoders. Of course you might get lucky. There will certainly be some really well made >100k cheap encoders go out and you're well in front. There will also be some that aren't so great at these price points.
To get the mechanical construction precision required on a consistent basis to take full advantage of these mega resolution step encoders you would need to spend several thousand $$$$. They are out there by the way. You can get them from a company like Heidenhain
http://www.heidenhain.com/ Unfortunately a high resolution pair will cost as much as most telescopes.
Cheers