From: Milton Aupperle <milton@outcastsoft.com>

Date: April 26, 2010 11:39:46 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Encoder  self-correction question....

Hi Alberto;

That's basically what PEC is. The only difference is that PEC relies on you tracking / correcting a star, and that's subject to turbulence so you need a very steady night to do it or possibly miss corrections too.

A high resolution encoder should remove the need for the star and the turbulence uncertainty factor and human error, but would likely need to be an Arc second or smaller in read out to be worth doing.

Basically what I would envision is that a device is clamped to the RA axis, and then a PEC recording session is made with the amount of drift over several cycles measured. Then this data is processed and a series of PEC offsets are generated and fed back into the PEC for the scope. The next time you use the scope, you can turn PEC on and it corrects all the defects. You could do this task day or night too.

Unfortunately, all the low end mounts I know of do not allow one to read or write the PEC data directly into the mount. So this would have to be done manually by likely putting a fake star on the screen and having you push the hand controller buttons to move the star. Of course there is no feedback from your presses on the hand controller going into Astro IIDC, so you can't tell if you made the right correction or not. So I can't really see it working unless one can upload the PEC Corrections.

And a device already exists that monitors it, so I can't really see a lot of incentive to do this.

TTYL..

Milton Aupperle

On 26-Apr-10, at 9:12 AM, albe albo wrote:

Hello to all.

I just saw the "real" device that I figured out in my mind since long time ago  

The principle is very simple and i guess that many people thought to it: a encoder that reads the AR axis rotation detecting any error ( periodic or not)  in real time allowing a real time correction.

A kind of autoguide without stars.

Some years ago,when  i thought to such device i was answered that such encoder was a dream and that it didn't exist but now i see that someone did such corrector.

The interesting fact is that changing the mechanical adapter will allow to transport the device on different mounts.

Someone have feedback about it?

http://www.mda-telescoop.com/index.php?option=com_content&task=view&id=52&Itemid=82

Now i was thinking to a Mac - Astro IIDC software based version of such device simply buying an encoder (i found one with 3,6 arcsec resolution) and attaching it directly to the AR axis.

I was thinking that even a  resolution > of 1 arcsec could be used because the software could read the "trend"  and correct it.

http://www.microesys.com/drcEncoders/pdfDRC/Model%20M35%20Data%20Sheet.pdf

The question for Milton: is such kind of correction so different from an autoguiding?

Which kind of conversion is needed between the phisical encoder and the USB port in order to simulate the data that AstroIIDC get from the guide star?

That device send its control pulse trough the ST4 port like a normal autoguide.

It could be interesting to do some experiments (even with rougher encoders) in order to understand the feasibility.

Thank you for the attention

Alberto