Advice with meridian flips

[Spookyer (Brett)]

Hi all

My plan for the weekend has me imaging M31 Andromeda from around 9.30pm to 1.30am. It transits at 11.37pm. As I understand it my mount will therefore be on the "wrong" side for the last two hours. I believe it will just keep tracking. My first question is as long as I watch it and nothing gets caught or is going to hit the tripod legs then that is ok?

Second question - if I do have to do a flip while tracking a target at some stage I gather I do this

• reselect the object (mount would flip automatically)
• rotate my DSLR 180° (or as close to this as I can)
• reframe as closely as possible I guess by taking test images and moving the scope to try and match the images pre flip.
• Find and guide star and restart guiding
• In post rely on Pixinsight to stack the images even though those after the flip will be slightly different to the pre flip shots?

Is the above correct or should I be doing something different?

Given the above hassles I guess it is preferable to just image past the meridian if possible?

I am using an AP Mach1 mount 132mm refractor and a Nikon DSLR.

thanks for any advice.

[RickS (Rick)]

G'day Brett,

So long as you don't try to slew the Mach 1 ought to just keep tracking past the meridian. If you want to be sure you can set a meridian delay from the driver or from the hand control. As you suggest, tracking past the meridian is fine so long as you don't run the scope or camera into the tripod.

If a flip does happen you will need to ensure you get the object back in the frame. This is where plate solving comes in really handy! You can rotate the camera by 180 degrees if you want but you don't really need to. PI will register the subs even if they are flipped. You will need to acquire a new guide star and re-start guiding.

I do flips in the middle of imaging runs all the time. It's not that big a deal if you're prepared for it.

Cheers,
Rick.

[Spookyer (Brett)]

Thanks Rick. Without a plate solving capability though I just have to try and get the framing as close to pre flip as I can and let Pixinsight flip and then merge the two sets of subs together even though they will be a bit out?

The Mach 1 manual says it will track past the meridian so I not sure what the meridian delay feature actually does?

Brett

[RickS (Rick)]

Brett,

It won't matter if the subs pre and post flip aren't in perfect registration. The PI registration process will take care of any difference in translation or rotation (or even scaling, but that shouldn't be an issue here). You don't want them to be too far out though, because you'll need to crop areas where the subs don't overlap.

The mount will track past the meridian but once you pass it doing a slew will automatically cause a flip. Meridian delay allows you to move the time at which this happens forward or backward by a number of hours. For example, if your object transits at 1am and you set a delay of 2 hours then a slew won't cause a flip until 3am or later.

Cheers,
Rick.

[Spookyer (Brett)]

Cheers Rick