Sunday, July 11, 2010

Auto-Guiding with PhD

I constructed a Meade 505 compatible serial cable so that I could upgrade the firmware on my Autostar 497 hand controller. The pinout for this cable can be found on Mike Weasner's Meade Autostar Information page. I'm reproducing the schematic diagram here:

The only challenge was wiring the RJ12 (4P4C) connector; I had to buy a crimper specifically for it. Most crimpers cost $20 to $30, but I found a really cheap one for $3.00 but it cannot crimp RJ45 connectors (it's purely for telephone cables).

The black dongle above is a Targus PA088E USB-to-serial converter; then a short RS-232 cable; and finally my home-made Meade 505 cable.

I got the ASCOM Platform files from ASCOM Standards, and the drivers for "Meade LX200 Classic and Autostar #494, #495, and #497 (combined telescope/focuser, 5.0.3)" from the scope drivers page on the same site.

Everything worked great out of the box, although it took PhD quite some time to connect to the Autostar (I thought it was hung).

I used the Philips Toucam as the guider; a bit of a challenge because it's not very sensitive and the sensor is so small. I used my William-Optics Zenithstar 70ED as the guide scope, and there was no payload. This scope is f/6.2 so if I use a 50mm f/1.8 standard lens as my guider, I should have less troubles with the sensitivity (or lack thereof) of the Toucam. The wider field of the 50mm lens on the tiny ICX098BQ sensor will also make life a lot easier.

I got an RMS of 0.36 (which I've read is pretty good) out of the box! and no major RA errors to be had. There was a persistent error in DEC that would take PhD some time to correct, I believe this is due to my lack of polar alignment, so I have to do a bit of tweaking.

Still, very good results! now I see why over-mounting is so important; the Zenithstar is rock-solid on the Great Polaris, even with the big imbalance (the standard counterweight is too heavy).

So now all that's left for me is to find some dark-sky site and good weather!

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