Meridian Flips - Trying to Understand.

[AlistairW]

Hello,

I have avoided doing Meridian Flips primarily because I don't understand them. I mostly image, and pick my objects based on whether they have passed the meridian or not. Anyway, I feel I must be missing out. My set up is on a pier, if that is of importance, - and I understand how to set up the necessary processes in the software, but I have yet to do one. So lets say I pick object X before transit, and image away, I presume once the transit time 'happens' the scope re-orientates. Is it as simple as that ? - Do people avoid doing flips and do it manually (I can imagine cable snags etc.). Does having a pier mean I can imagine  past the transit time anyway, - indeed does a pier limit the need to flip ?  (I was thinking about having a go at the Heat & Soul Nebula tonight).

Thanks

Alistair

[carastro]

I have almost always done a manual meridian flip, I agree about the cables etc and personally think it's safer that way.  Plus it happens between subs and not during one.

My biggest problem is I often lose the target when I flip, possibly because my alignment is not 100% perfect, and then spend ages trying to re-find it.  I guess it is easier if you use plate solving.   Also the image will be upside down after the flip.  I normally find the best way to flip is to re-ask the mount to GOTO the target again and if past the meridian will automatically flip.  Not sure how it works with EQMOd, possibly the same way.

Carole 

 

[AlistairW]

Thanks Carole.

[Ouroboros]

Same here. I'm meridian flip averse. I tend to let it run on gathering images past the meridian as long as they look ok.  Like Alastair I tend to choose my targets to avoid the flip. On occasion I've waited a few minutes until the target has crossed the median before calibrating guiding and starting imaging. But I'll be very interested to hear how others deal with this, perhaps in a slightly more efficient way than I do. 

[chrisshillito]

Being flip averse is always the best course of action in my opinion.  Certianly automated flips are one of the most dangerous movements the mount, and its attached equipment will make. The weight shifts and speed of movement involved will put fixings to the maximum test not to mention the risk of cable snags. And when the flip is complete you have all the hassle of guide star re-quisition, image reframing, possible re-calibration, image rotation etc.

It seems to me that many folks assume that just becasue a mount/automation software can do an automated flip it must be a good idea and they don't consider carefully enough if it is actually required.  Many mount setups will track well past the meridian - how far will depend on your equipment and the declination of the target. Preparation is the key -  goto your target and then slew in RA to see just how far you can track before there is a collsion risk . The difference between the RA of your target and the RA at the collision point will tell you how many hours/minutesd/seconds you will have before a flip is necessary - you may be pleasently suprised just how much time you can get. If using EQMOD I would advise setting an appropriate RA limit. If your is object close to the meridian at the start of your session you might consider preflipping the mount so it starts in a counterweights up position and tracks through into a normal counterweights down position (EQMOD will do these "flipped gotos").

Chris.

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[carastro]

Yes having read other comments, I agree. I do image well past the Meridian if I can get away with it.  Generally depends which scope I have on the mount and whether there is going to be any clash with tripod/pier.  

Also I can never get  my head around whether a target is before or after the Meridian, so I tend to just look at the mount to see how far it is slewed and which direction it is going in, I soon find out but can't really plan in advance, so you're one up on me on that basis. 

Carole 

[paraman]

2 hours ago, carastro said:

Yes having read other comments, I agree. I do image well past the Meridian if I can get away with it.  Generally depends which scope I have on the mount and whether there is going to be any clash with tripod/pier.  

Also I can never get  my head around whether a target is before or after the Meridian, so I tend to just look at the mount to see how far it is slewed and which direction it is going in, I soon find out but can't really plan in advance, so you're one up on me on that basis. 

Carole 

You can always check out your target in stellarium Carole, open sky and viewing options, then markings and tick meridian then you can see where it is in relation  to the meridian. If you also tick equatorial grid then you can get a good idea of time to flip.

[carastro]

Quote

You can always check out your target in stellarium Carole, open sky and viewing options, then markings and tick meridian then you can see where it is in relation  to the meridian. If you also tick equatorial grid then you can get a good idea of time to flip.

Thanks for the advice Roger, I'll bear that in mind.

Carole 

 

[AlistairW]

Thanks for all the advice ?

[ollypenrice]

I applaud Chris, who is a software guy par excellence , for advising caution on automated flips. Very realistic advice. Flips can be automated but careful cable management is of the essence and PA has to be excellent. Your guiding parameters will need to be corrected as well. If you are going to re-frame manually (by eye) rather than by plate solving then I think it best to open a pre-flip image in another programme and rotate it 180 to use as a model for your reframing. That way you won't end up with rotated darks and flats and so on, as you may if your capture programme lets you software-rotate the post flip captures.

On the plus side, combning pre- and post- flip subs can combat noise and gradients.

What a game!

Olly

[MattJenko]

As much as I agree with the sentiment of the above posts, they do lack a certain element of amateur imaging and that is pragmatism. Sometimes a target just needs a flip in the middle, and that middle will often be at stupid o clock. Lowish southern sky objects are a prime example. They have limited imaging time and cross the meridian. It almost mandates a flip if you are to capture such objects.

If you understand that you need to master the flip, then a lot of the concerns voiced above are valid, but with thought and practice, they can be overcome. Cable management is a simple, testable affair in daytime. Using software to attempt an automated flip is not impossible. The key is platesolving and to allow the target to pass a certain amount past the meridian, otherwise when you slew across, your platesolving stands little chance if the mount limits don't allow the target to be fully re-centered, which is often the case right on the meridian itself. There is always going to be an element of rotation and off centering when the image is basically upside down, so be mindful that targets filling the field of view are not good candidates and that an mosaic attempt will need wider overlaps than non flipped images, but for me, the waking in the morning and seeing the scope pointing the right way after an unattended successful flip is most satisfying. I have had my share of failures, don't get me wrong, but I would be missing out on a huge range of opportunities and sleep if I adopted a never flip policy.

[Davey-T]

One of the few plus points of a fork / wedge mounted scope, no meridian flips 

Dave

[ChrisLX200]

A meridian flip @ 14deg/sec is a non-event with my current mount, and with the use of a saddle stand-off plate there is no chance of a collision even when pointing at the zenith. Cables are routed to avoid any possibility of snags - arranging for that is not rocket science. With my old Losamndy G11 there was certainly the need to plate-solve back onto target and re-aquire a guidestar but SGPro and PHD2 between them took care of that automatically (mostly). I did not have the stand-off plate with the G11 so I had to be aware of the possibility of the camera hitting the pier - and that was dependant on the height (altitude/DEC) of the target. I never bothered to adjust weight bias East or West of the pier, it tracked well enough either side when guided. DSS will align correctly regardless of which side of the mount the image was taken, but you may end up with significant stacking artifacts (black borders) if the scope is not precisely on target again after the flip.

ChrisH

[ollypenrice]

2 hours ago, MattJenko said:

As much as I agree with the sentiment of the above posts, they do lack a certain element of amateur imaging and that is pragmatism. Sometimes a target just needs a flip in the middle, and that middle will often be at stupid o clock. Lowish southern sky objects are a prime example. They have limited imaging time and cross the meridian. It almost mandates a flip if you are to capture such objects.

If you understand that you need to master the flip, then a lot of the concerns voiced above are valid, but with thought and practice, they can be overcome. Cable management is a simple, testable affair in daytime. Using software to attempt an automated flip is not impossible. The key is platesolving and to allow the target to pass a certain amount past the meridian, otherwise when you slew across, your platesolving stands little chance if the mount limits don't allow the target to be fully re-centered, which is often the case right on the meridian itself. There is always going to be an element of rotation and off centering when the image is basically upside down, so be mindful that targets filling the field of view are not good candidates and that an mosaic attempt will need wider overlaps than non flipped images, but for me, the waking in the morning and seeing the scope pointing the right way after an unattended successful flip is most satisfying. I have had my share of failures, don't get me wrong, but I would be missing out on a huge range of opportunities and sleep if I adopted a never flip policy.

I can go much further past the meridian when imaging low targets because the bottom of the scope doesn't encounter the pier. It's the high merdian transits which usually impose a flip sooner for me.

But I agree with your post. There's no avoiding them so get on top of them!

Olly