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Thread: Meridian Flip

  1. #1
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    Default Meridian Flip



    Hi Group,

    I am sure that this question has been asked at least 1000 times. Maybe more.
    If I’m lucky enough to have a good night this week, I plan to take a try imaging M51.
    For instance, At 10 o’clock p.m. on Tuesday night, M51 is about 39° off the horizon. At just ather 2 a.m., M51 will cross the meridian at 71 degrees off the horizon.

    My question is: If my camera is not going to collide with the mount during and after their meridian crossing, do I still have to do the flip? Never having done a flip before I am avoiding that. At 2 AM, I don’t know if I’ll feel like rebalancing we focusing and continuing imaging. But, if I must, I will give it a try.

    Thanks for your help,

    Jim
    Scopes: Explore Scientific ED102 Triplet APO, Celestron Nexstar 130 SLT.
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    Default Re: Meridian Flip

    I believe you should be OK without doing the flip and without rebalancing. Just remember that the mount has a setting for maximum travel beyond meridian. It will stop at that point. My CGEM's default value was 15 or 20 degrees, but I've set mine to 10 because of camera/tripod crashes
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    Default Re: Meridian Flip

    I used to avoid flips, Now they cost me a bit of imaging time, but are no big deal.

    You need to determine your own equipment's limits to avoid collisions. Let's say you can go one hour beyond the meridian without any risk. Set your mount's slew limit to permit say 50 minutes after the meridian. Then set your software's limit to 45 minutes.

    That way, you can continue imaging for 45 minutes after your target culminates. At that point, your software should either perform the flip or abort tracking. If for some reason, the software fails to do so, your mount should either flip or abort tracking five minutes later. And if both fail, you have ten minutes to manually stop it before something bad happens. Obviously, revise the numbers based on your own equipment's clearance.

    Balancing for an automated flip is an artform. I balance my mount a little bit counterweight-heavy. This makes it a bit east-heavy in the eastern hemisphere. It makes it west-heavy after the flip. But my iOpteron CEM60 has very smooth, low-friction operation compared to a Synta mount. So whereas the thick sludge that Synta uses as grease would have gravity fighting with it through the backlash as the counterweights descend on the west side, the iOptron mount lets gravity win and the tracking smoothly lowers the counterweights with no backlash issues.

    It you are going to be doing automatic flips during an imaging session, you might want to do a tuneup on the mount with a light grease.

    I would strongly recommend using plate solving to regain your framing after the flip. SGP takes a plate-solve image just before it flips, then plate-solves again after it to regain the same aiming point. This minimizes cropping when you stack the before and after frames.
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    Default Re: Meridian Flip

    What Kathy said. In short, it depends on your mount.
    If you use SGP with platesolving, and if your PHD is hooked up through ASCOM, everything is automated. My system will do a flip and start reacquiring data after about a 5 minute delay or less.
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    Default Re: Meridian Flip

    Hi and thank you all for your responses!

    I looked into SGP and unfortunately, my Nikon D3300 is not supported. It is not supported by most camera control software, so it looks like I will just have to experiment with what I have and make the best of it.
    I use DigicamControl and although it lacks many features, it works well with my D3300. Maybe sometime in the future, I will upgrade to a different dslr or AP camera, but it won’t be anytime soon.

    I will try to image on one side of the meridian for now. If I can get a chance to shoot M51 this week, I will just start imaging when it is low (39 degrees) and I should be able to get about four hours before the target is near the meridian.

    Thanks again,
    Jim
    Scopes: Explore Scientific ED102 Triplet APO, Celestron Nexstar 130 SLT.
    Mounts: Celestron AVX with Orion MM Autoguider, SLT; Binoculars: Bushnell 10X50;
    Camera: Nikon D3300 and D5300(unmodded), Astrophotography Tool, PHD2, SharpCap v3.2, StarTools, PE14
    Dog: Jack
    Astro Photos https://flickr.com/photos/157183480@N07/sets/72157707681236785

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