Gday Chris
Quote:
|
If you don't use 2 discrete values then then how can you account for a mount that isn't perfectly polar aligned? If the angles aren't 90deg apart then it's a good sign your alignment is wrong.
|
For the given step sizes, any polar misalignment error will be negligible,
and the scope was relatively well polar aligned
The angles in question are used to convert the sensor axes to the true RA/DEC axes. The calibration process tells the scope to move in an EW direction and notes the angle and direction that makes on the chip.
It then moves in a N/S direction and again notes the angle and direction.
The EW error angle/direction should become the absolute datum and then the NS angle will be 90deg to that and in the "direction" measured by the cal,
ie RA and DEC cannot be anything other than 90deg apart,
certainly not over 20deg, which is what we saw.
Quote:
|
Also I can guess that during calibration the PE of the RA axis would be so insignificantly small compared to the step sizes used for calibration that it probably doesn't matter.
|
Maybe, maybe not.
The mount we were testing had an RA drift of 10-15arcsec/min plus a large PE that sometimes matched this. ie In some spots we were seeing local RA error rates of up to 30arcsec/min
Its the only reason i can see that the cal results were so far away from 90deg apart.
Anyway, irrespective of this, i now know that PHD2 converts "for display" based on its cal angles, as I wrote an app to convert the raw X,Y to RA/DEC based on RA being the master angle ( with DEC normal to RA ) and the plots start to make more sense.
I am just suggesting that this is something that you should look at if the data looks suss. I also recon PHD2 should throw a warning if an oddball cal gets registered, as usually, noone looks at that data.
Andrew