Is there a way I can tell SGP how much before/after the meridian it can do the flip? I’m doing 20 minute NB exposures, and I can get away with flipping about ten minutes early or late, but I’m not sure how to let SGP know that. I suspect this is in the merdian flip box, but I’m not quite understanding the manual on this.
Kevin
If you check the “Wait For Meridian” option, SGP will check to see if the target will cross the meridian during the next exposure. If it will, SGP will hold off starting the next exposure; wait for the target to cross the meridian; do the meridian flip process; and then resume the exposure.
If you don’t check that option, you can use the “Minutes Past Meridian To Flip” option. For example, setting it to 10 minutes, says If the next exposure will complete by 10 minutes past the meridian, go ahead and start the exposure; else wait.
This is all about pier collision. For some setups, no amount of meridian crossing can happen without collision; maybe its OK for your scope to image past the meridian up to xx minutes.
If you don’t use either, SGP will simple check at the end of each exposure to see if the target has crossed the meridian. If it has, do a flip. If not, start the next exposure.
Charlie
Thanks Charlie. Glad I asked. I wouldn’t have guessed that it meant that. So just to be sure: I uncheck Wait for Meridian and set Minutes Past Meridian to Flip to 15, and I’m doing 20 minute exposures. If an exposure finishes at meridian minus 6 minutes, the next exposure will start. If instead the exposure finishes at meridian minus 4 minutes, SGP will wait four minutes, flip, then start the next exposure. Correct?
With my setup - C11 on an MX+ on a SkyShed pier - I can flip anywhere from 15 minutes early to 15 minutes late. And I take 20 minute NB exposures. So with 30 minutes of leeway it seems to me that I should be able to flip without ever needing to wait. But there’s no way to set that up, is there?
Thanks again for the help.
Kevin
A note of caution - flipping too early can be as bad as flipping too late - as it potentially causes a clash on the other side. I routinely had ‘wait’ option enabled and had flawless execution. For some reason I became impatient and unchecked it. I had a number of instances where 20-min exposures exceeded the flipping point (set to 10 min) - in which the exposure duration exceeded the minutes past meridian value. If you follow the logic, it would have flipped too early. A shorter exposure duration would have been OK.
So to be safe, I would always choose wait for meridian option, as you know precisely when it will flip.
buzz, I’m safe flipping anywhere from 15 minutes early to 15 minutes late. I’m just not sure I understand how the controls are interpreted by SGP. Do I have it wrong in my description above (first paragraph of post 3)? If I set the controls as I outlined, will it not wait at all, and just flip when it falls in that window? That would be fine, but I want to make sure that’s what’s supposed to happen.
Kevin
I have mine set to 10 minutes in SGP - and the mount is OK up to 30 minutes either way. If I have wait for meridian checked, SGP checks if the next exposure will go past the 10 minute flipping point. If it does, it will not start the exposure but wait until the 10 min past meridian and then flip, with a pop up option dialog asking you if you want to flip early.
In my experience, if I uncheck the wait dialog, I have had 20 min exposures start and go past the 10-minute flip point. That might be deliberate, based on not going more than 10 minutes the other way, or it potentially be a bug.
I was about to ask a similar thing. The past two nights, I had a related issue where the meridian limit was reached with my Mach 1. I’m also using APCC, so once the meridian limit is reached, the scope stops tracking. This prevented a meridian flip. I’m thinking of using the wait for meridian option from now on as I lost half a night due to this bug.
You are correct. If 15m past meridian is set in SGP, a 20m exposure will start at meridian -6m.
However, flipping early is probably not going to work. As I understand it, most ASCOM drivers do not support early flips. When attempting to flip, SGP simply issues a new “go to” the target coordinates. The ASCOM driver looks to see if the target is on the west side of the meridian and the scope is also on the west side of the meridian. If so it will perform a flip. If the target has not yet crossed the meridian, no flip will occur. So if the go-to is issued with the target still 10 minutes east of the meridian, no flip.
Some ASCOM drivers (Astro-Physics, for example) have “meridian delay” options that affect when a flip will occur but I seem to remember previous discussions of the AP meridian delay and it didn’t allow an early flip by SGP.
Charlie
maybe i am using this thing wrong. but here is what i see. AP mach1gto with APCC.
although this setup is meant to prevent pier crashes, i’ve had one or two in this configuration. this is because i had asked APCC to merely stop tracking when the limit is reached, but in certain circumstances either SGP or PHD2 sent commands to the mount which caused it to start tracking again. it would be nice if APCC had “stop tracking and park in place”. i think to be totally safe as things stand, i’d have to set APCC to “park to default park position” when the limit is reached.
the usual situation with this setup is that an exposure ends somewhere past the true meridian, and then even though the system is eligible for a flip, SGP waits until its delayed meridian is reached before it attempts the flip. if i happen to be watching the system, i can click “attempt flip now” button in the dialog that comes up and avoid wasted time. otherwise i lose up to ~29 minutes of imaging time.
if i understand the preceding discussion correctly, unchecking “wait for meridian” might solve this situation, but only if the delayed meridian in SGP is set to > subexposure length. otherwise SGP could attempt to cause a meridian flip before the true meridian is reached, which on an AP mount with no meridian delay would not cause a meridian flip.
IIRC the problem with early meridian flips and SGP is that the AP driver does not expose a particular ASCOM property that SGP needs to support it. and according to chris rowland the real solution is a new set of ASCOM properties which drivers would use to indicate how much more time the current pointing state is ‘safe’, as well as how much time until the opposite pointing state is ‘safe’. this would let you configure how early and late of a meridian flip is safe in your system.
I think I’m starting to understand. The question I still have is:
Does the flip happen at meridan minus 4, meridian, or meridian + 15?
Kevin
Another frame will be started, and it will flip after that frame completes. This is also the case if you are 13 minutes past the meridian and your frame finishes.
“Wait For Meridian” should probably be renamed to “Wait for flip”. Ideally you want to meridian flip as soon as your setup can if you’re not using “Wait For Meridian”. This will give you the most leeway between images and also not require your setup to just sit and wait.
In your example if you had “Wait for meridian” enabled, your system would sit there and wait for 19 minutes as it couldn’t start another exposure. But this is generally better than potentially crashing into the pier.
I recommend flipping as early as possible and not using the “Wait For Meridian” unless you need to. So when do you need to? When the reachable area between pier sides is at or below your exposure length + some buffer time. I would recommend a 5-10 minute buffer time to account for plate solving, auto focus, and other tasks that may take place. So if you’re taking 20 minute exposures then you want 30 minutes of tracking past your flip point. If you don’t have that then you should use “Wait for Meridian” to help prevent a potential pier crash under the worst case scenario.
Hope that helps,
Jared
Thanks Jared. That helps. Yeah, I have 15 minutes on either side of the pier, but not 30. It seems like the best option for me is to leave Minutes Past Meridian to Flip at 0, and to check Wait for Meridian. At least that way I can get an option to flip early if I happen to be watching my gear at the time. (But I also seem to remember someone saying they had solved this problem by adjusting settings in both SGP and TSX. Of course I can’t find that post.)
So to summarize, the rules are:
Correct? Sorry for being so slow on this, but the whole meridian flip thing is still new to me.
Kevin
You know your setup better than me. But if you’re able to reach 15 minutes on either side of the meridian that means you have 30 minutes in which you can safely execute a flip…assuming your hardware can flip pre-meridian. If that’s the case, and you typically do 20 minute subs or less, I’d setup your meridian flip to happen at -15 (15 minutes prior to the meridian) and NOT user the Wait for Meridian option. That means if the “worst case” happens and an image starts 15:01 before the meridian that you’ll have some time for the auto focus, some time for the sub and still a little wiggle room for safety.
Yes, those two statements are correct.
Thanks,
Jared
Oh right, that should solve everything. I’ll check that out tomorrow. Thanks again.
Kevin
so does “wait for meridian” just cause the dialog box to come up? meaning if everything is working well the way i have it set up, and since it’s safe for me to flip right at the real meridian, i should just turn off “wait for meridian” and the mount will flip as soon as that last exposure ends?
I hope I understand what you are asking, pfile…
You could substitute the following words for “wait for meridian”:
SGP is ready to take the next frame. It will check to see if the next frame can be completed before it hits the meridian. If it can be completed, it will start the exposure. If it cannot be completed, it will sit and wait until the mount has tracked into the meridian. It will then initiate a meridan flip and continue imaging from the other side of the pier.
Conversely, if the box isn’t checked, SGP will check at the end of each exposure and see if the mount has passed the meridian. If not, it will start the next exposure. If it has, it will perform a flip.
For this second option to be usable, you should be able to track the length of your exposure plus some buffer (for example, the time to do an autofocus) past the meridian without danger of hitting the pier. This is what I use with my 1100. I don’t mess with delays or anything, I just let it track past the meridian to complete the image it is working on, then allow it to flip.
Best regards,
Craig
yes, i can probably track up to 2h past the meridian if the camera rotation is favorable and about 1h past if the rotation is unfavorable (the STT filter wheel is not symmetrical.)
so i have SGP set to flip around 30mins past the meridian, and APCC set to stop tracking around 40mins past the meridian, because i can’t make assumptions about the rotator angle of course.
i think i have had ‘wait for meridian’ incorrectly checked all these years. all i want SGP to do is to 1) let an exposure continue past the meridian if need be, and 2) not attempt to flip before the meridian has been hit. since at the most i’m using 30min exposures, it sounds like what i should do is set SGP to flip at the meridian, uncheck “wait for meridian”, and leave APCC set to 40mins. then in the worst case SGP should initiate a flip 30 mins + change after the meridian, so those extra 10 minutes should be enough to solve/sync/flip without APCC stopping the mount.
rob
Rob,
I still don’t think that is quite it…
I think that having SGP set to flip 30 minutes past the meridian means that SGP effectively acts like the meridian has shifted to 30 minutes later. So it will use a time that is 30 minutes after the mount would hit the meridian to decide whether to flip. That isn’t what you are after, based on your description. Instead, you should not set any delay in SGP and set APCC’s meridian limits for 40 minutes after the meridian for a fail-safe if something goes awry. And, as you say, uncheck “wait for meridian.” With those settings you will generally be shooting or finishing up an image as the mount tracks across the meridian, then SGP will initiate a flip after the completion of that image but before it starts another one.
As I mentioned, this is exactly what I do. It is simple and reliable.
Best regards,
Craig
Dang. I tried to set Minutes Past Meridian to Flip to -15, and got a message that my mount doesn’t allow flips before the meridian. Paramount MX+ using the ASCOM driver (which I think is required by SGP). I don’t know if this is determined by the ASCOM driver, the mount, or TheSkyX, but I don’t see any way around it. It looks like I’m stuck with losing the imaging time.
Kevin
the 2nd paragraph of my reply describes (again) how i have it set up right now, not what i am proposing to change.
the 3rd paragraph is my restating of what you have told me,
by “flip at the meridian” i mean to not set any delay at all in SGP (flip at the true meridian)
the reason i had “wait for meridian” checked in the first place is that i was always under the impression that SGP might try to initiate a flip before the meridian if it was unchecked. i was working off the idea that some mounts can be explicitly commanded to do a meridian flip at any time, while with an AP mount the only way that happens is if you do a slew to the target with counterweights up. if SGP tried to flip before the meridian, no flip would happen, and a pier crash could eventually occur. i set all this up before APCC existed; now i think there’s not as much danger if SGP fails to flip (but there is still some danger as i mentioned above).
rob