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ASI Air Pro calibration


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With the new ASI Air Pro firmware, you seem to be able to keep an existing calibration (or you can delete it and start a new one). 

If I aim towards Orion (which is roughly south and at zero DEC) and calibrate there, should I then use that calibration even if I move to a different position. 

For example, when I moved the scope towards M97, and recalibrated, it came up with a message that the calibration was quite different to the previous one (which I assume was because of the different RA/DEC position).

Should I simply have used the original calibration (from when I pointed at Orion) rather than recalibrated? 


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In PHD2, if you have a connection that supplies the mount's RA and Dec, then you can Cal near Dec =0, and use that Cal on all your Targets for that night.

If the mount doesn't supply RA and Dec, as in a basic ST4 setup, you will have to recal on every new target.

Whether those rules apply to ASIAIR's version of PHD2 is something that may be described in the instructions.


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At dec 0 the mount moves the maximum distance for a given guide pulse - as measured on the sensor. Conversely, at the pole there is no visible RA movement no matter how big the guide pulse.

When you reuse your calibration at different declinations the RA pulses are scaled according to where the calibration was done. By calibrating near dec 0 you get the most accurate scaling.

You can of course calibrate on every target but reusing your calibrations can save a lot of time.

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As above and direct from the manual:

If you're using an ASCOM (or Indi) connection for either the 'mount' or 'aux-mount', a good calibration can be re-used for a long time, and that is
the preferred way to operate. These connection options allow PHD2 to know where the telescope is pointing, so a calibration done at one point
in the sky will be automatically adjusted as you slew to different targets. The old method of having to re-calibrate whenever you slewed the scope
or switched the side-of-pier is a thing of the past so long as PHD2 has pointing information. With this type of set-up, you would only re-calibrate if
you rotate the position of the guide camera by more than a few degrees or make other major changes to the hardware configuration. In general,
the best practice is to get a good calibration within about +/- 20 degrees of the celestial equator and high enough in the sky to avoid major seeing
(turbulence) problems

You can always review the results of your last calibration by using the 'Tools' menu and clicking on 'Review Calibration Data' That will open a
dialog that shows a graphical representation of the mount's movements along with the values that were computed for guiding your mount. This
window is described elsewhere in the Calibration Details section of the help file. As a quick quality check, you can open this window and confirm
that 1) the RA and Dec lines are roughly perpendicular and 2) the plotted points are roughly linear with no significant curves, bends, clumping of
points, or reversals in direction. If you do see these kinds of odd patterns in the graph, you should probably re-do the calibration

Edited by scotty38
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2 hours ago, michael8554 said:

Fleshed-out descriptions above are good, but I'll repeat, that if your setup is basic ST4, you'll need to Calibrate on every new target.


Agreed and the manual extract does say that.

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