@geehalel thank you SO MUCH for your work. Indeed, having a driver available to track correctly to be able to plate solve as a quick sync technique would be amazing. Let me know whenever there is something to test. All my very best and again, thank you. Federico
@geehalel: regarding your question of the field rotation axis: I guess as long as the axis of the mount and the guide scope are parallel, the center of the rotation axis should be the center of the sensor, i.e. the distance between mount axis and guide scope axis is far too small to cause any parallax as the points projected on the sensor are at infinity. Things should become more complicated, once both axes are not (perfectly) aligned: in the extreme case of the guide scope axis being perpendicular to the mount axis, there is no more rotation, only translation. In between there should be a mix between rotation and translation, i.e. the center of rotation is moved away from the center of the sensor. My understanding is, that the deviation introduced by such misalignment is what is coined "cone error". Maybe you find some hints in the logic regarding cone error correction to model this; there should also be some literature where this is being described / worked out.
Does this makes sense ?
on second thought: as long as both axes are not perfectly aligned, the center of rotation moves rapidly away from the center of the sensor: let´s assume we have a 1.5 degree fov with our guide scope. If the alignment error between mount and guide scope axis is more than 0.75 degrees, the center of rotation is already off the sensor. I think you can calculate the center of rotation by calculating the fov of your guide scope / sensor combination and substract the deviation angle of the scope axis and mount axis in degrees. How many pixels this equates to, you can derive from the fov calculation. The direction of the deviation should be the opposite of the axis deviation in relation to the sensor orientation.
This is without guarantee. Just my understanding.
on a third thought: I probably should have rather asked you, what you are aiming at. With my hints above, I was in "equatorial mode". In Alt-Az there is no rotational axis of the rig itself. If you want to derotate the exposures made on an alt-az mount, I think the way to go is by star pattern alignment, i.e. agnostic of any mechanical rotation calculation.
Dear @geehalel, @knro et all,
Here's a picture I did yesterday using Stellarmate with my AZ-GTI working in ALT-AZ, Nikon D5100, and SkyWatcher 127 MAK, just one exposure of 30 seconds:
I used Synscan driver - just launched Synscan Pro app, did a one-star alignment with a star nearby the Orion nebulae, then goto Orion nebulae and alignment using Stellarmate astrometry.
Look how well defined the stars are, given that this is a somewhat long exposure and that it was in ALT-AZ, and that I only have done a one-star alignment.
I think if I repeat and align over 3 or 4 nearby stars before goto Orion, I could probably get even more dot-like stars and definition at even longer exposure times.
Of course, this opens the door wide-open to shorter exposure astrophotography, I did 10-second exposures, and then the stars were perfect dots.
This speaks volumes about how awesome the AZ-GTI is (especially given its price). This quality might not be enough for professional astrophotography (I think it might, if perfected a little) but it definitely is enough for EAA!
If only the AZ-GTI driver could do the same the Synscan Pro app do, then we would not need that app as an intermediary and we could start even faster: just turn on AZ-GTI, do alignment-sync using astrometry, boom, ready to start working.
Let me know your thoughts,
Only wanted to reiterate my continued interest in this topic...
@geehalel: I guess I owe you an apology regarding my newbee comments concerning the field rotation: I was actually not aware that you are Jean-Luc, the creator of the EQmod driver. If I would have known, I would have spared you these trvialities...
Anyway, I hope you are making progress regarding the Alt-Az driver ?
Once again, the power of AZ-GTI in Alt-Az mode. I just walked out around 11PM in Poitiers, France (urban area, clean sky though), installed the mount on a Gitzmo lightweight photo tripod, launched the Synscan Pro app, did one star alignment to Rigel, connected Stellarmate with Synscan driver, did one Sync with astrometry, then goto M42. Then 100x10sec frames at 800ISO with my D5100 hacked DSLR through a 127" sky-watcher MAK, plus some dark and bias, then stack, boom.
Having a driver that can do this without having to bother about connection issues in the background to the Synscan app would be tremendous!