Guiding experience

[Peter Somogyi]

I've created this topic to share my 1st experiences with guiding on a ~12mag object (with 250/1000 scope + Alpy guide module).
I expect here a deep discussion (couldn't find this topic by sorting each alphabetically....)

Last weekend I've got a new Lodestar X2, retiring my ASI 130mm (the yellow 1/2" one!) putting it on a 50mm focus canon objective lens so that now I'm able to (re-)teach the scope very easily via wifi remotely... Otherwise, that chip is a very common and being used widely for guiding in AP world....

Switching to Lodestar X2, the change is astonishing. Random noise patterns are gone (though have taken and used darks)!
Instead of 4-8 sec noisy guide star (nearly disappearing) at 2x2 bin of the ASI, now with the X2 gone down for 1 sec with a clear and stable star shape !! (at 2x2 bin) Which means 0.5 sec for positioning, 1 sec is to make sure won't get it lost when going to sleep.

Although 2x2 binning brought approx. extra 0.5-1 mag ability for the ASI, it's still a pain finding any object due to its noise! (I suspect these cams are optimized for fast reads for moon & planets rather than low noise.)
Once I moved to Metaguide becasue PHD[2] didn't like ASI drivers. But later found that ASI recommends WDM-style driver that solved the crashes/hangs.

There are 2 places you can use darks... in PHD2 there's a main icon, but common driver page also offers it... PHD2-one should be used I think.

Some tuning I made during last night in PHD2 with the 2x2-binned X2:
- "RA min", "Dec min" had to set to 0.10 instead of 0.50, otherwise guiding won't happen at subpixel precision !!! guiding graph in PHD2 smoothed a lot!
- set aggressivity to 70% from 100%, somewhat reducing oscilations
- don't know what hysteresis means, altering the 10% didn't bring improvement.
- 2x2 avg and 3x3 median filtering turned to better be switched off, caused higher oscillations on the guiding graph
What I still don't see perfect, is guide shots statistics view... it's still asymmetric, maybe the scope wasn't balanced enough, or having too big backlash (where can I set it? does PHD2 recognize backlash at all?).

Now a word about finding middle of slit at subpixel precision. I did it at the same 2x2 bin, but slided the "lock position" while put the detector in loop maxing out the histogram + watching star shape to be symmetric, pressing the up/down button at 0.10 precision in PHD2 while guiding on a bright star finding the optimal value.
Then the ref. star was taken with the same setting. This step was really needed I think because of the huge binned pixels.

Attaching the X2 to Alpy: there's an approx. 10mm I had to pull it outwards beyond the ring, therefore focusing + rotating was a series of tries. (Missing adapter for the extra 10mm...)
Focusing: was using a Bahtinov mask (at f4 it can't be skipped), but first I had to focus the scope to have the narrowest spectra on the G3 ccd (hopefully had to be done once). Only then focused the X2. But next I'll use only scope focuser... It's also a question why focus is different there...

As for the Alpy slit mirror, I have defects on the surface - a few holes (not on the slit), hope it won't affect reflectivity near the slit.

The other big improvement of X2 is finding the star... having noiseless 0.5s instead noisy 4 sec or so is a big relief! Now finding 12 mag star and dragging it to the slit is not a pain anymore!

PS.: ASI reseller writes it has a UV/IR cut filter, but I couldn't find or disassemble it... Maybe it's an error from me here (IR/UV blocks lot of light, especiall in IR where that chip is exceptional...). But I really needed it for remote goto [re-]teaching...

Any more thoughts/experiences welcome.