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Old 17-06-2020, 12:48 AM
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Stonius (Markus)
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To cross the meridian or not?

Does anyone here image across the meridian in a single session? As in, track an object up to the meridian. Stop, tracking, cross meridian, plate solve, focus and continue tracking? I know it's *possible and sequencing programs are set up to achieve this, but it seems to me that there are several potential issues that have kept me wary:


  1. If you use the 'slightly unbalanced scope' trick to make the gears engage nicely, once you cross the meridian, it will be the opposite weighting and tracking will be worse, wouldn't it?
  2. Supposedly optical components may realign as they move across the meridian (ie, mirror flop) but I'm not sure why this should be the case, since my telescope is never 'upside-down' on a GEM.
  3. If you're not at your telescope, there are more things that can go wrong with big moves, like cable snags, failed focus, failed platesolves which would seem to be more likely to happen when switching from one side to the other.
So...is it best to stick to one side of the Meridian or not?


Cheers


Markus
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Old 17-06-2020, 01:41 AM
glend (Glen)
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Markus, when I was imaging I did used to image across the Meridian but without all the hoopla. By that I mean my mount, a CGX has the ability to image continuously across the Meridian by up to 20 degrees. Often I was asleep while that was going on, but SGP would alert me via email if necessary. I had Teamviewer running from the Observatory laptop to my little Netbook next to my bed.
Caveats, never did it with any SCT, would not own one anyway, too many problems, only newts and refractors, proper imaging rigs. The CGX had internal soft and hard stops, so it was in no danger of going too far. By imaging continuously across there was no need to plate solve after a flip.Balance was rarerly an issue as the CGX is a good belt drive mount with spring loaded worms, and i would run pretty neutral weight, but a tad nose heavy.
So again, only through the Meridian up to the soft stop setting, which was 20 degrees past the Meridian. But I always prefer the East side, as in that direction I was imaging over the Pacific, never below 40 degrees (which is usually where I would start). Once past the Meridian trees came into play past 20 degrees over anyway, so no need to go further. And you know there is always another night.
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Old 17-06-2020, 05:46 AM
Startrek (Martin)
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Depends on the location of the object in the sky for your field of view , how much data you need and what object your imaging in regards to crossing the meridian. Not everyone has a clean view of their target tracking on one whole side ( trees, house next door , transmission tower etc... )
I image on both sides and donít have any issues with a flip, framing up again and tracking and guiding , sometimes donít even move the counterweights
Cheers
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Old 17-06-2020, 08:51 AM
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Stonius (Markus)
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Ah, so you do have two different counterweight positions depending which side of the meridian you're on? Makes sense.
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Old 17-06-2020, 10:15 AM
Startrek (Martin)
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Yes, generally counterweights should be slightly east heavy
In my case it means moving my counterweights only 10mm or so up or down to achieve this. Sometimes I donít even move them on the other side of the meridian and everything still tracks and guides ok
I Goto and track with EQMOD so you can set your limits 5 to 10 degrees past the meridian and then the mount will auto return to the home position ready for slewing to object again on the other side
Itís a great piece of software, been around for 12 years and itís free ( only works with Orion and Skywatcher ( Synta ) mounts though , unless there has been recent updates to the list of mounts.
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Old 17-06-2020, 11:30 AM
glend (Glen)
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Markus, it is generally accepted that gear driven mounts need weight applied to the gears to keep meshed, as you traverse the Meridian weight actually neutralizes and then backs to the other side, causing tracking problems, etc, which is why people who flip normally shift weight. However, not all mounts require this
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Old 22-06-2020, 01:32 PM
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I am going to go against the grain a bit here. I have been imaging both sides of the meridian on a nightly basis ever since I got automated flips going and was happy that my cable management will ensure that I won't see any snags. And that was with my SCT as well as my refractor (I wouldn't go out and buy the SCT I have now as an imaging scope, it was my visual scope and I use it to image because I have it)

Provided you get all your mechanical alignment and setup right there is no reason for plate solving to fail after a flip, the only times this happened to me were in the setup and refinement phase as I got it all working and it was inevitably a problem of my own making.

I run my RA axis somewhat unbalanced (The AZEQ6 and AZEQ6 derived mounts are not easy to balance properly in RA anyway) so the gear loading while it will change direction before and after the flip should be enough to keep the worm meshed both sides, it still tracks and guides OK to the west in my experience.

You do need to be sure of your cable management and of your mount limits (Software or hard stops) to ensure no cable tangles or equipment crashes and in the case of the SCT in particular, automated focus is a must so that you can make a focus run after the flip and regularly thereafter in case of mirror movement. If you are chasing a particular target, why waste up to half the night by only imaging on one side?
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Old 22-06-2020, 03:56 PM
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multiweb (Marc)
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Quote:
Originally Posted by Stonius View Post
Does anyone here image across the meridian in a single session? As in, track an object up to the meridian. Stop, tracking, cross meridian, plate solve, focus and continue tracking? I know it's *possible and sequencing programs are set up to achieve this, but it seems to me that there are several potential issues that have kept me wary:


  1. If you use the 'slightly unbalanced scope' trick to make the gears engage nicely, once you cross the meridian, it will be the opposite weighting and tracking will be worse, wouldn't it?
  2. Supposedly optical components may realign as they move across the meridian (ie, mirror flop) but I'm not sure why this should be the case, since my telescope is never 'upside-down' on a GEM.
  3. If you're not at your telescope, there are more things that can go wrong with big moves, like cable snags, failed focus, failed platesolves which would seem to be more likely to happen when switching from one side to the other.
So...is it best to stick to one side of the Meridian or not?


Cheers


Markus
Should talk to Peter (peter_4059). He's got that down pat in SGP I think.
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Old 22-06-2020, 07:57 PM
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I've done ever since I switched to SGPro. Set it up and it goes all night. I have my scope balanced, not one-sided heavy. I don't get much diff in tracking either side (but I modded my mount to run on belt driven steppers - made a huge difference). Just get it to autofocus after the flip.
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Old 23-06-2020, 10:33 AM
RugbyRene (Rene)
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I regularly image past the meridian especially if I know the target goes close to the zenith. Luckily I have the software (KStars) that manages it all for me provided I input the correct config (i.e when to perform the flip). And as others have said, you want to make sure your cable management is up to the task.

It's not fool proof and I have woken to find my scope in odd positions, but I'd say 90% of the time it works flawlessly.

Rene
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Old 23-06-2020, 03:51 PM
Imme (Jon)
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I use SGP to do it basically every session without issue (so far).

Scope is balanced and I donít see any real issue tracking either side of meridian (it is tuned though). EQ6 carrying 13.5kg.
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Old 23-06-2020, 05:10 PM
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Atmos (Colin)
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The moment I got auto focusing running was the moment I stopped getting up for meridian. I stopped worrying about being east/west heavy, just balanced reasonably well and the trusty EQ6 did the rest. This is while I was running SGP and PHD2 via EQMOD on the old EQ6. I did lose a sub here and there due to poor tracking but I found that happened regardless of meridian side or east/west heavy balance. Gremlins are always there lurking in the background
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Old 04-07-2020, 10:37 PM
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As Colin said, SGP will happily meridian flip and plate solve an EQ6 or HEQ5 with reasonable reliability. If it fails to reacqure and track well then you're no worse off for data. If it does then you may get hours more data - albeit with a sub or two lost when the RA re-establishes reliable meshing.

The higher the quality of the mount and tracking the greater the reliability. More recent belt driven mounts with low backlash probably fine.
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Old 05-07-2020, 07:36 AM
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I offer another vote for implementing meridian flip, automated where possible. The main reason is not losing the opportunity to grab data whilst the object is visible in the night sky. Our clear skies are too precious to waste.
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Old 05-07-2020, 09:26 AM
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I would go further than Rob has said about reliability. There is nothing inherent in the EQ5/6 and related mounts to prevent them doing automated flips reliably, you just have to get the settings right.

For SGP I needed to widen the default pointing limits in EQMOD (This would have applied to Voyager too) or it would hit a meridian limit during the flip process and fail (It is likely a lot of people do not turn on limits in EQMOD so they would not run in to this one, at the risk of an equipment crash at some point) as soon as I widened the limits, reliable flips.

Voyager, I would have needed to set the wide mount limits for Voyager if I had not done already while I was using SGP. Voyager also behaves differently, where SGP stops and waits for the target to cross the meridian Voyager images through it for a time that is defined by the user, in my case, about 20 minutes after the meridian triggers the flip. If a sub is underway at that time it will run as far as 30 minutes after the meridian to complete the sub before aborting it and flipping. Why waste a sub in the best part of the sky?



I had to delay the flip a fair way past the meridian in Voyager due to foibles of a cheap mount. I originally had it set to flip at 5 minutes after the meridian, the cone error in the system (and ALL mount/scope combos will have some amount of it) would result in the plate solve returning a position east of the meridian and when Voyager syncs the mount position after plate solving EQMOD would reject the sync and then the plate solved pointing fails operation fails. I checked how far my gear could safely go past the meridian (About two hours in the worst case) set EQMOD to stop the mount about 30 minutes before that for safety and set Voyager up to flip no later than 30 minutes after the meridian. Perfectly reliable flips since then.


It is just a matter of understanding how your mount and the software you are using behaves and sorting out settings to suit.
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Old 05-07-2020, 12:14 PM
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RobF (Rob)
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Agree with Paul you have to get to know your gear, and certainly supervise a dozen or so flips to see where the risk factors for gear, cables, and re-establishing tracking are.

From memory think I have SGP set to run 10-15 mins post meridian before flipping. EQMOD has a "pier side" pointing model which works well if you do have a bit of mesh/backlash issues with your mount.

Most software will have limits you can widen for solve, sync etc to give things time to settle.
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Old 06-07-2020, 06:18 AM
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The_bluester (Paul)
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It was a while before I trusted it to do unattended flips, you really have to be sure of your cable management to do that and of how everything behaves. I have seen a lot of setups that would end up with ports pulled out of cameras and laptops lying in the dirt of you tried it.

The ex tech in me made me sort my cables a long time before I tried for automated flips.
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