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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Camera rotation to compose image and/of find guide star

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I am imaging with a 9.25 SCT at f/10. My imaging train includes: an OAG (with Lodestar camera), a Filter-wheel and an SBIG CCD. These are all screwed together and held to the scope with a Baader Click-lock adapter. The FOV of the Lodestar is only 8 arc-min while the SBIG is roughly 24 arc-min. Last week, when the skies were clear, I had trouble finding a guide star for a couple of targets (this is unusual and I may have just been unlucky in my camera orientation and choice of target). But it suggested to me that I may need to be able to rotate my camera chain. To this end I have ordered a 2" par-focal ring that I can lock behind the Click-lock, so I can rotate the cameras without moving too far off focus.

My questions here have to do with my workflow , for imaging, with camera rotation and how do people 'compose' images using Kstars/Ekos by rotating their camera? Unfortunately we are expecting several nights of rain, so I cannot just go out and try it, so asking here is the next best thing.

Does EKOS establish the camera orientation when I do a plate solve and sync? Is this reflected in the camera FOV view in Kstars? Or do I have to input the angle of camera orientation someplace?
It seems I need to establish the FOV and the relationship of both cameras so I can preset the camera orientation to assure I will find a guide star. Or is it a process of trial and repeat?

Does anyone have any insights concerning what my process should be once I have added the capability to rotate the cameras orientation and how Kstars/Ekos will assist me in both finding a guide star and 'composing' the image on the target.

thanks,
Ron
3 years 9 months ago #55473

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I should add that I use Phd2 guiding, and it seems that Phd2 has no way of knowing that I rotated the camera (I have asked a similar question on their forum). I don't know where the 'decision' to re-calibrate before guiding resides. if I have checked the box in Ekos setup Not to re-calibrate on slewing to new target, but if the mount is not responding as expected , because of the camera orientation change, then somewhere it needs to re-calibrate (I assume).

How would Ekos respond if I used the internal guiding?

thanks,
Ron
3 years 9 months ago #55474

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Once you rotate, you have to recalibrate, but that's all. You just repeat your plate solve, recalibrate the guiding and you are set.
3 years 9 months ago #55477

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Does the added plate solve establish the new orientation of the camera? And that shows up in the Kstars star map as the camera FOV?

Ron
3 years 9 months ago #55479

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Yes and yes.

That happens after every meridian flip. In the vast majority of cases, the camera is not perfectly aligned at 90 degrees rotation, but at 80 and some degrees. After the flip, you will see the rotation angle changing to 90 something degrees.
With every solve the rotation angle is determined anew.
Last edit: 3 years 9 months ago by Jose Corazon.
3 years 9 months ago #55483

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When you plate solve the solved frame will be placed on the star map and the value of the Rotation will be updated in the Align module in EKOS. You can also find that information in the camera's INDI driver under the WCS tab.
You should then be able to use that value and set the rotation of your FOV pointers. But I just tried that and noticed they don't match correctly and will be posting about that as an issue shortly.
3 years 9 months ago #55484

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3 years 9 months ago #55486

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First, to clear up some misconceptions. FOV symbols are merely guides on the star map. They are completely independent from anything taking place within EKOS.
As it stands currently EKOS does not modify the position or rotation of the symbols. The EKOS Alignment features will however mark the solved FOV with a fixed in place frame on the star map.

Part of that bug report is an unexpected offset in the solved value, which should be well defined in the simulator configuration. In principle the simulators should closely emulate real world equipment. But my bug report could be an issue with the simulator itself, and not with the Alignment subsystem itself. Hopefully that will be sorted out in my bug report thread.
Then in addition the interpretation of degrees of rotation when applied as a custom FOV was not displaying as expected either. Why the interpretations are different is one question I seek to resolve. It may have something to do with a difference in Degrees Clockwise, as defined in CCD Simulator, and Degrees East of North as defined in the FOV symbol editor.

Now, it is true that the offset does not move about the center of the pointer when a rotation is set. Unfortunately that is something to bring up as an improvements under the Wishlist section. So in the meantime you could work out the offset for any degree of rotation with trigonometry of a right triangle, XYZ, with only 2 values z & X. The Offset from center will be the hypotenuse Side z, and the angle of rotation, Angle X
Offset X = z*SinX
Offset Y = z*CosX
Not the ideal situation, but if you don't change your rotation frequently, it is certainly functional.
Last edit: 3 years 9 months ago by Andrew.
3 years 9 months ago #55503

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Thank you for responding here. Yes, I understand that is a transformation I can make on the custom FOV symbol. I will post to the wish list the capability to rotate the camera/guide camera combination about the center of the guide camera offset, but it certainly is not critical. I would like to know where the finder FOV is relative to the main camera to see if I expect to find a guide star. But in practice it seems that may not be to useful; as I will first have to actually slew to a target (it does not seem that there is a way to predetermine what orientation the camera will take at the target before you actually slew there - at least I will have to think about that or at least pay attention to camera orientation after slewing to understand that). Once actually there I can look to see if there is a guide star (which then means I do not need to re-calibrate guiding - so that will be the first choice). If not then I will rotate the camera system until I find a guide star, (refocus if necessary), re-calibrate guiding (here it seems Phd2 has an advantage because with it you can erase the old calibration data and tell it to re-calibrate; I believe with the internal guider I would have to turn on the option to re-calibrate after every slew in order to do that and I really don't want to re-calibrate after every slew - if there is a way to just tell the internal guider to re-calibrate 'now' that would be useful).

thanks again for helping me understand some of these intricacies of the program.

Ron
3 years 9 months ago #55530

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What you probably could do is solve position for the main cam, then for the guide cam, and determine the distance of the two FOV centers.
Then define a circle centered on the main cam center, with that distance as radius. Or two of them, with min and max distance. Gives at least some hint...
3 years 9 months ago #55536

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Yes, I will have to come up with some strategy for finding the right orientation so there is a decent guide star in the guider FOV. But right now it has to STOP RAINING!! Almost another week of rain predicted, we had nearly 18" in May, here in Eastern NC.

thanks,
Ron
3 years 9 months ago #55547

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As Ihoujin pointed out in his Bug thread, turning on the DSS option in the HiPS Overlay really helps. I probably would not have found the HiPS Overlay if he had not mentioned it. I can easily rotate the custom FOV symbols (as already pointed out) and that does help in framing an image in my sensor. The Sensor FOV, that you can toggle on and off on the right hand side of the toolbar panel, is the one that I thought might be rotated by the WCS setting (after all there is an option to 'set' that rotation angle in the Indi control panel). But no matter, once I slew to a target and establish what the current orientation of the camera is I can use the Custom FOV symbol (toggled on the left side of the toolbar panel) to rotate it for framing or finding a guide star, note the angle and then rotate the camera assembly accordingly. Another plate solve will show how close I am to the desired orientation.

The internal plate solver, with the source extractor, as been working pretty well; even with my narrow FOV setting (26 x 20) for this current setup.

thanks again,
Ron
3 years 9 months ago #55576

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