[gregbradley]

I got a replacement worm sent for free bySoftware Bisque several weeks ago. I haven't been able to get to the mount due to work.

I did last night and successfully changed the worm and readjusted the cam thanks to the helpful video from Chris Venter.

I did a 10 minute image and got elongated stars, quite badly elongated too. It was windy and that was not helping for sure but the elongations were from tracking/PE issues not the wind as I strategically position the slide off flat roof to minimise wind and I was using my AP140 which is not partcularly wind prone.

I also did several automated t-point runs and that is now working quite reliably (I got on top of that last trip and it remains working - yeah!).

I adjusted the polar alignment until I got a perfect report from t-point. Odd behaviour occassionally with t-point. It can be slightly erratic.
I did a 24 point run and it told me to raise the altitude by 8.8 ticks. I did that. I ran it again and did a 48 point model and it told me to lower it by 8.5 ticks! I did. I ran about another 44 point model and it said it was perfect.

I also did a new PEC curve and the resulting curve did not seem to affect guiding.

I did another PEC using 2x2 binning instead of 3x3 binning. It gave a better curve and one that looked more like the one on my PME that works so well. Its more subtle and only small sections above and below the middle line rather than large.

So I conclude from this that 2x2 binning is way more accurate than 3x3 is on a 1050mm focal length refractor. Also seeing was not great due to the wind. I wonder if I should try one at 1x1 binning to get even higher resolution.

So now I have a new PEC and perfectly polar aligned it was time for the acid test - more exposure runs.

Oops, more elongated stars and very very odd autoguiding where the guide star oscillated between 2 points back and forth and I was getting 2.39 pixel errors in guiding which is massive (I want below about .3).

I immediately thought this must be some sort of backlash issue. Perhaps I did not tension the drive belt correctly but I thought it was done the same as Chris did on his video.

I slide the counterweight further down the shaft to put more weight bias (the RA shaft was nearly horizontal and I wondered if it was too balanced). I also recallibrated the autoguider just in case something was way off there.

I also went for much longer guide exposures and reduced the aggressiveness down a lot (to 3). Bingo - guide errors routinely low - between 0.00 and .4 mostly.

I also slid the dewshield down from full extension to keep it out of the wind stream. That helped a bit.

5 minute subs were now showing perfect guiding. I was using a MMOAG and an SBIG STi guider. Woohoo!

I think the PE was so low that the autoguider was causing its own oscillations and I needed to turn the guider way down. I may need to turn it down even further as the polar alignment is very very spot on.

No sign of a spike in PE (there was a bit of black rubbery thread on the belt, I wonder if that was part of the spike I was getting, the worm did not appear to be damaged in any way although perhaps scratches may only need to be tiny to affect guiding and grease hides some of that).

So it looks like I have a working PMX and most likely a working PEC curve (to be verified tonight).

Next step is a 300 point t-point model with Protrack corrections as well as PEC corrections and 15 minute subs. That's tonight if its clear enough.

Gee, I even did some imaging for once!

Perhaps I could even whack a 12 inch OOAG on this baby now or a CDK 12.5 inch (probably not, too wind prone but OOAG only has half the tube sticking up in the air).


Greg