Quote:
Originally Posted by ericwbenson
Hi Bart,
After you get the basics setup, such as:
1) OAG orientation: square to main imager and above main chip is a good start
2) Camera orientation: up-down = North South. Verify by turning on image crosshair and slewing star with hand paddle, it should stay near the line. Image might be flipped left-right or upside down, don't worry about that.
3) Set the Lodestar binning to 2, always, it cleans up the venetian blind effect and makes for more sensitive pixels.
4) Calibration: nice L shape (just make sure the calibration times are long enough). DEC backlash will show up here, not much you can do about it.
The following is optional but will improve picking up faint guide stars. If you are going to choose your guide star manually you can skip:
5) Capture a set of bias and 10 sec darks (10-20 frames each should be fine) using the Autosave in Camera Control, you won't be using longer than 10 sec guide exposures I expect!
6) Go to Process...Set Calibration and import these frames, use sigma clipping (default settings) and Autoscale darks. Before exiting hit the "Replace with Masters" button. Exit dialog
7) Now you can use Options...Full calibration on the CCD guider window to calibrate the guider frames
Even more optional:
8) Process...Create Master frames, pick the Dark master frame for the guider and go into Process...Replace Bad Pixels. Hit Auto generate, use Dead pixel threshold=95 and hot pixel threshold= 300, ok. Change the map name to something like SXL2x2_c95_h300, save map, exit, don't save changes to master file.
9) Go back into Process...Set Calibration and pick the master dark and assign a Bad Pixel Map.
10) Tune the AG loop. Find a star that hits 20-40K counts in ~1 sec exposure. Start with aggressiveness zero on both axes, watch the guider graph. The ugly RA sinusoid and erratic DEC drift line are what you're AG is fighting, it won't always win, but you hope it can get a draw...
Increase aggr to 2 on one axis, watch a few minutes hope thing improve, increase by two more, watch some more, etc. Never go beyond 8, try to use 6 or 7 if your mount is smooth enough. Repeat for the other axis.
Watch the RMS number it is more important than peak-to-peak. NB it might be in pixels, multiply by guider image scale to get arcseconds:
(guider scale = 206 * binning * pixel_size_um / focal_length_mm)
so in your case gs = 412 * 8.3 / EFL.
RMS < 0.5" is ok, < 0.3" is good, < 0.1" is fantastic, beware this will scale with guiding quality AND local seeing conditions, so a good moonlit night is best (you don't feel guilty about wasting imaging time!)
That's it. If your still not happy, better look at a bigger mount :>
HTH,
EB
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Hi,
Thanks for the informative post. I will give this a go.
Cheers.
