Missing global/profile option for rotators

Rotate camera to default option seems to be “+/- 180 deg”, i hope an a global or profile option could be added to change this default to “always”
In my opinion it’s an easy option to overlook and it can create problems with flats not fitting if half the subs are taken at 0 and the rest are taken at 180

That seems reasonable. I can change that.

I might be misunderstanding the request to change from “+/- 180 deg” to “always” as the default. I’m not sure how others use this option but I always keep and use the “+/- 180 deg”. This way after the Meridian flip the rotator does not need to rotate the camera and I don’t need to do an additional set of flats. If I’m understanding the request correctly, by changing the default to “Always” that would mean for folks like me, I will now need to remember to change the default from “Always” to “+/- 180 deg”. “Always” means after a meridian flip the rotator will rotate the camera which means I’ll need to take additional flats where as “+/- 180 deg” would mean I do not need to take additional flats?

Maybe I’m confused on what is being requested and agreed to?


I might not have desribed correctly what i wanted…So lets try again.

A few days ago i imaged M31 doing a mosaic, it was done over several nights and had other targets running before M31 was started.
What i found was happening is that the rotator didn’t go to the same position every time M31 started to i had to take a double set of flats.
I guess SGP moved the rotator to the closest position of where it was for the earlier target, what i’d like to happen is for the rotator to return to the exact same position instead of having a chance being opposite.

I guess this would need another setting? “Always” would mean the camera would be rotated 180 degrees after meridian flip and +/- 180 would mean there’s a chance of the position being wrong at the start of the target depending on the positon it was in before centering/rotating was started.

Thanks for the clarification, I see the potential problem now when imaging either over several nights and/or mosaics and how the “+/- 180 deg” setting might cause the issue. I don’t do mosaics but I do image the same target over several nights and have never had the issue where the rotator flipped to the opposite side on the start of other nights. It has always stayed on the same side and always fell within my tolerance range. I typically set it to +/-0.5 degrees and never had any issues with my flats. However, I can see how it would be possible to have the rotator rotate 180 degees opposite and that would give you the problem with flats…

what you bring up is an interesting problem. Maybe Ken already understood the issue and knows how to address it.


I hope so, it would definitely be great if it could be solved because i have several mosaics planned :slight_smile:

Here’s the M31 image, at first i could not figure out why i was uneven untill i checked the angle and found i had to sort the images and take 2 sets of flats.
It’s 8 panels and it consists of just 1x 300s each of L, R, G, and B per panel.
If you open the full size image here it’s still just 25% of the original image size.

Is there any update on if this will be added in an beta coming soon?
Starting some mosaics soon i’d love to see it added :slight_smile:

I think we may have initially misunderstood what was asked here. It sounds like you’re wanting something along the lines of “Maintain Rotator Angle”. Essentially if you start imaging at 90 degrees on the east side of the meridian to force the 270 on the west side of the meridian (rotator does not move). Where this really becomes important is with multiple targets. So the ±180 behavior would just pick the closest. The “Always” option would makes sure you were always at 90 degrees (meaning that the rotator moves after a meridian flip).

Is that essentially what you’re after. Something that essentially just keeps the OTA and the chip in the same orientation regardless of the side of meridian for a target? If so, this is a good deal more complicated than what I believe Ken was initially agreeing to. Not impossible. Just we need to keep track of some additional parameters. I do believe this is a good suggestion though.


I think I’m now in a similar situation with my new system. I have a rotator, but it is solely for framing. I run the system unguided so there is no need to hunt for guide stars etc.

So in my view the options are either to:

  • a) keep the sky angle constant so that guide star stays on chip before/after meridian flip, or
  • b) keep the mechanical angle constant regardless of the pier side which will avoid the need for separate east/west flats.

I think that b) could be fixed quite easily if you always choose the sky angle < 180 degrees when slewing on the west side and the sky angle >= 180 on the east side of the pier. Something like that would make the rotation consistent between runs, and keep the rotator in place during a meridian flip. Choosing the angle that is the easiest to get to e.g. after a previous target is absolutely wrong here. How do I then know the angle in which to take the flats?

++ Jari

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Jari explains it much better than i could :+1:
I don’t need it for guidestars either, it’s just for the problem with flats not fitting.

Great, we are on the same page then! I’ll tag @Jared here to make sure he sees the outcome.

One simplification on the logic of b), a predictable mechanical angle can be achieved easily by only using mechanical rotation angles from 0 to 180 degrees. So if the requested sky angle results in desired mechanical angle of 235 degrees the rotator would be moved to the 235 % 180 = 55 degree position.

++ Jari

Any progress on a solution to fix this problem?

No progress here. This will not be addressed in the 3.1 release. We’ll try to get to this afterward…

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Ok, thanks for the update :+1: