VX mount, PE

[Erquy]

Hi,

just wanted to share about my new VX mount: I measured the PE (by taking pictures 0f 10 minutes long and measuring the distance peak to peak and recalculate then the arc/sec, non polar aligned and without using a specific PE software): I found about 38 to 46 arc/sec peak to peak on 1 worm cycle (the values are extreme peak to peak I found done on 4 worm cycles)

After PEC training (note I am learning PEC training), manually done using liveview zoom in Canon utility with a simulated reticle (so maybe not the best way to do it and only 1 PEC training, not using a batch), I achieved going down to about 12 arc/sec peak to peak. This allow me to take aout >90% good shots (well rounded stars) for 1 min exposure at F10 with my C8 (I took 20 pictures and only need to reject 2 and still relatively small shift in 1 case which is more due to DEC shift than RA shift, I could still use it), unguided. Prior to PEC training, I would say only 60-70% were OK to my taste and mostly due to RA shift.

Below a 250*250 pixel of a star from 1 min unguided picture taken through the C8 at F10 with Canon EOS 1100d

note that all of the PEC correction is done manually and measured on picture. PEC not done with autoguider nor measurement done by some specific software like pempro and the like (so still rought measurement, and I hope I am not wrong in my calculation!)

What´s your opinion? Has anybody something to report on PE of the VX mount?

Regards

[Tiki]

I did something similar with my SP. I can't remember the peak to peak figures but I got a mostly smooth sinusoidal curve. There was just one portion of about 1/5 of a period that went a bit scatty. I stacked sixty one minute subs straight on top of one another and analysed the result with Image J (freeware).

[Erquy]

Hi

I did another PEC training and also took 3*5 min with PEC and 3*5 minutes without PEC playback.

Below snapshot. Quite a difference!!

According to this picture, without PEC, peak to peak is about 30 arc.sec and with PEC, only 5!

Below picture is Cebalrai and was taken at f25 with the C8 slightly not polar aligned

[Erquy]

Hi,

I now uploaded some data in PECtool. above 2 runs of PEC done over 2 different nights -so based on different polar alignment- (data after "drift removal" as polar align was not spot on when I did the training): I am amazed how the curves are similar even in small variation!. Still to work out another 3 and average it.

In my calculation above, I was wrong as I think I was well polar aligned, and difficult to consider drift in the calculation. So according to the data, PE is about 17-18 arc sec (and with correction, as seen on above picture, I am down to some 4 arc sec).

[Erquy]

Hi,

Finally I run 5 PEC training and averaged them. I obtained RMS error of 1,09 and a peak to peak of 18.2 on the average (made by PECtools). So pretty good if one compare with other data reported out there on other mounts.

Regards

[Chris Rowland]

This matches what I've found with my AVX, P-P error without PEC about 35 arc seconds, after PEC training (5 cycles using a guider) RMS error 2.6 arc seconds.

That PEC graph looks similar to mine, one big cycle and one small. Each cycle very similar.

Chris

[Erquy]

Hi,

after fine tuning my PEC curve on several runs, now I can get 100% usable 1 min subs at F10 (2000 mm) :

http://stargazerslounge.com/gallery/image/19045-altair/

nice sharp stars in the middle, of course cannot do much on the edges.

I tried above 2 min at F10 but it is then going down to 60-70% usable and I think shall work 2min above >90% with reducer at F6,3