I'm not getting how iPolar would need to have the mount leveled. Once the calibration process (multiple plate-solved images rotated around the RA axis) is done, the iPolar should have a model of the camera's relationship to the RA axis, right? That's how it knows where to put the red dot on the display. And since it's plate solving to put up its target circle, it already knows not just its pitch/yaw orientation but its roll too, i.e. the rotational angle of the RA axis WRT the sky. Doesn't matter whether it's in the same orientation as last time -- putting the dot in the circle should mean that the axis is pointing at the Pole, no?
I freely admit that I may be wrong -- I have the worst spatial intelligence of anyone I know (even our cats).
Let's say, you align perfectly tonight, tomorrow you set up your mount again, but now the ground is soggy and one tripod leg ends up lower than the other, tilting the mount by 1 or 2 degrees.
Everything else being equal, how would iPolar know that mount is not level or the camera rotation angle has changed, etc?
If the coordinate system remains identical, then, yes, it would work, but if the coordinate system has changed, I cannot see how iPolar would solve that problem with one variable too many. Accounting for that 3rd variable is the entire reason for rotating the mount for PA determination in Ekos.
Please correct me if I am wrong here.
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Welp, I don't own one so I can't test it. Working from some admitted level of ignorance here!
But after calibration, the camera/computer/gadget has a model of its relationship to the RA axis, and that only changes if the camera in the axis gets bumped.
And by shooting a picture and plate solving it, it can see that, whoops, it's not pointing in the right place anymore. Now, if the soggitudinousness merely rotated the entire mount perfectly around the RA axis, certainly iPolar wouldn't know that, since it doesn't have a mount model per se. So your GOTOs would be off. But your polar alignment would still be awesome.
I would really like to do what you are doing an have been trying for a week or more. Is there any way you could give me a few pointers on your EKOS setup. I tried to run my CEM40G from Kstars on Astroberry but I couldn’t ever get iPolar to even connect to the camera. Perhaps a screen shot or 2. My guide camera comes up when iPolar is selected and no other way. It actually works but I havn’t been able to focus it yet. Also after 3 nights of driving the CEM40 it quit with a /dev/ttyUSB1 no such device error. I no longer works.
I am the ATM enthusiast, who built some astro stuff, including equatorial fork mount for my 10" OTA, ready for 70+kg load. I found, that the leveling the tripod (or a base in my case) is important for an ease of the polar alignment, but not essential, if you are going to do the polar alignment anyway. In general, in a range of reasonable positions, there is always possible to lift or lower the wedge and move it left or right enough, to aim the NCP, regardless the leveling. Thus I ask, why the "leveling" appears here so many time? Is it because of the GoTo? As long as the RA axis is aimed at the NCP (SCP...), the PHD(2) must work good and the long time exposures must be sharp. Am I right? I spoke with some astro photographers, they agree with me that they don't perform the multi-star alignment since they have the astrometry/plate solve. I know that it should be performed to build the model, but is it really essential?
I have also the iPolar camera and I think it's good enough to aim the mount roughly, but the Drift Align or other methods of obtaining the proper alignment should be performed anyway. Moreover, the iPolar is good enough for the astrophotography by short focal length OTAs, but isn't for 2500mm or more, where I am aiming.
Since I started this thread eons ago, I bought a CEM70 and now have a year's experience in actually using the iPolar. My experience is nothing like Wouter's -- my alignments (as checked by drift measurements in PHD2's Guide Assistant) are invariably within 10 arcminutes and usually within 6.
WRT the question of leveling or precise zero position, I can state categorically that leveling does not matter to iPolar. The key difference is that the camera is bolted into the axis, and so calibrating it yields a durable measurement of its displacement from that axis. Doesn't matter how you point or level the mount, because it's not attempting to decompose azimuth and altitude guidance. Unless the camera's alignment changes, the cross (representing the polar axis) will always be in the same pixel of the image. Plate solving lets it depict the dot (celestial pole) precisely. Superimpose the two and you're aligned.
Not willing to go as far out on a limb regarding zero position. But the CEM70 has a "find zero position" command which hunts in both RA and DEC until it's located -- I assume to a reasonable level of precision.
Having used it, now I understand one significant advantage iPolar possesses over Ekos PAA: since it's a wide-field camera, even if you just roughly eyeball the Pole, the target will be in the camera's FOV. Using Ekos PAA via your imaging OTA and camera, it's easy to wind up with a guide triangle that's several times larger, so you have to repeat the alignment process until the target is in view. If you're using long-focal-length optics, your result may be more precise than iPolar's, though the zoomed-in view makes a huge difference in that regard.
I'm now a firm convert to iPolar, its convenience trumps the necessity of directly connecting a Windows or Mac machine while I'm aligning. After that I just switch that USB cable to the Pi and continue the mission. The PAA's overwhelming advantage is its excellent performance when only the southern sky (for use N. hemisphere types) is visible.
Long focal lengths aren't really an issue because having the celestial pole in view is not necessary. In fact there have been some pretty significant improvements made to the EKOS PAA not long ago that make it possible to point away from the celestial pole and still calculate the correction vector. This is handy for situations where the view towards the pole is obstructed, or is very low.
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Waveshare Stepper Motor Board - DIY Focuser
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.
Happened back upon this thread and felt compelled to clear up a point: It's not having the celestial pole in view that's an issue with PAA and long-focal-length optics, it's the alignment triangle. If you weren't pretty close to start with -- always an issue with us itinerant imagers, not so much with those who have the luxury of leaving their setups undisturbed -- then the alignment triangle is going to extend beyond the FOV. So you have to iterate the PAA procedure until the target is within the FOV. For example, with my AT8RC and 183, the FOV is about 20' wide. Hard to eyeball the mount to that level of precision, especially with Polaris not in view!
What you say is/was true. However, check out indilib.org/forum/general/11816-announci...ignment-changes.html
Starting with the next release, or the current beta releases, you can complete a polar alignment in one iteration even if the error is larger than the field-of-view (if you choose the polar alignment "plate solve" algorithm in the correction phase).