using 2.6.0.23 (and previous versions exhibited this as well) - clicking “Center Now” in the target settings pane definitely centers the telescope, but it does not seem to also move the rotator to the angle given in the target settings.
the sky angle is definitely determined and propagated thru the system (the rotator section of the equipment settings updates to the correct sky angle) but the rotator is never moved by clicking Center Now.
thanks,
rob
That’s all that button ever did. Mostly because we were running out of real estate, we did not add the center and rotate option here. Instead, you can right click on the target and get to it that way.
ok, didn’t realize there was a pop-up menu. will try that, thanks.
on the topic, i’ve seen some discussion about mechanical angle vs. sky angle. do you have any plans to allow setting of particular mechanical angles vs. particular sky angles? i ask because i have some source of tilt somewhere in my imaging train such that the 0 degree sky angle position gives me bad stars in 2 corners. all other positions seem much better (mechanical 180, 90, 270). i haven’t been able to figure out what’s going on but i’m happy if i can set one of those “good” mechanical angles. since SGP uses sky angles i can’t reliably force a particular mechanical angle…
thanks
rob
You should always be able to correlate a mechanical angle to a sky angle. You’ll always have the same sky angle for the same mechanical angle assuming your rotator correctly reports a full 360 degrees.
Thanks,
Jared
well maybe i misunderstand something here, but if i ask for an “always” angle, say 0 degrees, then on one side of the meridian that’s going to be mechanical 0 and the other side mechanical 180. so the mechanical angle depends on the side-of-pier. on one side i get my desired mechanical angle and on the other side i don’t. right? because SGP is dealing with sky angles, not mechanical angles (right? - i mean, it has to be true since my rotator home position is not actually perfectly aligned with the sky, but SGP gets me to the right sky angle every time.)
if i instead configure the target to accept +/- 180, and the mechanical angle happens to be 0 at the start, no matter what the sky angle turns out to be (0 or 180), SGP won’t move the rotator. then after a meridian flip the sky angle will be 180 or 0, and SGP again will not move the rotator. i know this is true because that’s how i have SGP configured, and if i leave the rotator untouched at the start, i get the bad mechanical angle on both sides of the meridian. if instead i manually set the rotator to mechanical 180 before starting the sequence, then i get the good mechanical angle on both sides of the meridian.
so what am i missing? if i want to keep the mechanical angle of 180 on both sides of the meridian, what should i set as the angle in the target configuration, and how should i set the “always/accept +/- 180” control?
rob
The mechanical angle of a rotator (also referred to as instrumental angle) is absolute within the rotator. A rotator has an internal reference point (typically a magnetic or optical sensor) that is used as a method of telling the internal electronics were the rotator is positioned. For example, on my Optec Gemini rotator, performing a home function with the Optec control software causes the rotator to move in the CCW direction until the sensor is tripped. The rotator stops moving CCW and then moves CW 75 degrees and stops. This stopped position is considered instrumental angle zero and that is what is reported to a connecting (ASCOM) client.
If I connect SGP to the rotator after a homing function, SGP will report the rotator position as 0 degrees. Then I perform a “Solve and Sync” and that both initializes the RA and DEC of the scope and also syncs the rotator reading in SGP to the plate solved “sky angle” of the camera. In my case, the rotator is physically positioned on the back of the OTA so that the home position of instrumental angle zero plate solves to 90 degrees of sky position angle.
After the solve and sync, SGP knows the instrumental position angle of XX degrees (ie, 0 degrees) corresponds to a sky position angle of YY (ie, 90) degrees. So now SGP knows how to map the instrumental angle of the rotator to the sky position angle of the camera. From then on, SGP can move the rotator accurately to what ever sky position angle is specified for the target. During a meridian flip, I have the target option set to force the rotator to do 180 degree move (“Always”). So the sky position angle after the meridian flip is the same as it was before the flip. This keeps the same OAG guide star in PHD2 before and after the flip. Note that the 180 rotation after the meridian flip changes the instrumental position angle by180 degrees but keeps the sky position angle the same.
By using the Optec control software, I can position the rotator to any instrumental position angle I want. In SGP, the solve and sync puts SGP into sky position angle reporting. So when I move the rotator via SGP I am changing the camera’s sky position angle.
Charlie
i understand all that… your use case is probably the common one - “i need a particular guidestar to fall on my OAG no matter what side of the meridian i’m on”. that is what “always” is for and that’s how you’re using it. no matter what side of the meridian you’re on, if there was a star on the OAG, it will always be there, as the camera’s mechanical angle is rotated thru 180 degrees after a meridian flip.
my case is a little different: i don’t care what the sky angle is (X or X+180) as long as the mechanical angle is X. because as far as i can tell SGP is always dealing with sky angles, my use case is impossible to automate. as mentioned if i put the rotator at the mechanical angle that i want, then start a sequence with “accept +/- 180” then the camera never moves, which is what i want. but my point is that i have to make that first move by hand.
obviously in a properly functioning system this would not be necessary since either mechanical angle would be OK for a given sky angle. but as stated i have some pretty bad tilt at mechanical angle 0, so i need to avoid that angle.
rob
There is a specific mapping between your rotator’s position angle 0 and your camera’s sky position angle. You can determine that from a solve and sync. Then never setup a target that uses a sky PA anywhere near that position angle.
Charlie
do you not agree that 1) if “always” is set then the mechanical angle of the rotator will be X on one side of the meridian and X+180 on the other side of the meridian, and 2) if “+/- 180” is set then there are two possible mechanical angles for a given sky angle on either side of the meridian?
There are situations where the sky angle is paramount and others where the rotator’s hardware angle is paramount. In my case my setup is often changing and I have no need to set the oag angle to match the sky angle. At the same time, the rotator can very easily be calibrated so that its angle exactly matches the oag angle - and that lets me find the guide star directly.
So - if I don’t have an easy way just to specify the rotator angle itself - then it means SGP is insisting on doing something extra for me that I don’t want it to do. I want it just to set the rotator angle and record it in the fits header. It’s fine if it also measures the sky angle and stores that also - but I just want to set the rotator angle the way I want it to be set.
I could measure the offset of the sky angle with the rotator angle and write it down somewhere and add or subtract it - but that is pretty awkward and what I need to do is dead simple - but I can’t do it: Set the angle - start the sequence.
If I did measure the offset of the sky angle with the oag angle I would need to create a FOVI that had that offset built into it - which isn’t easy.
Frank
Your’re correct in #1 – if the option “Always” is selected, SGP will change the mechanical position angle of the rotator by 180 degrees during a meridian flip and that keeps the sky position angle reported by a plate solve the same on both sides of the meridian.
But in #2 – the “+/- 180” option will not move the rotator during a meridian flip so the mechanical angle of the rotator remains the same on both sides of the meridian. However, the sky position angle reported by a plate solve will change by 180 degrees after the flip.
Charlie
@chasmiller46 yes - and that is exactly how i am using the +/- 180 setting. my issue is that i have to manually put the rotator at the desired mechanical angle before starting.
let’s assume that the mechanical angle and sky angle are the same for the sake of argument. say then that i want 180 degrees mechanical/sky. so i set 180 degrees in the target. lets also assume that the rotator is at 0 sky/mechanical when the sequence starts.
when SGP starts up it solves the initial pointing image and determines that the sky angle is 0. however, since i have set +/- 180, SGP accepts the angle of 0 and never moves the rotator. therefore i can’t actually get SGP to move to mechanical angle 180 of its own accord. the only way to make that happen is to manually put the rotator at 180 degrees before starting the sequence.
my belief is that if the mechanical/sky angle happened to start out at say, 90, then whether or not SGP rotates to mechanical 180 depends on what side of the meridian the sequence starts on. but even if that’s not true, making this happen is predicated on my moving the rotator by hand before the sequence starts, which again is not very automatable.
rob