NINA and utilizing APCC meridian limits

Dale Ghent

Hi all, this aimed at users of APCC and NINA; specifically those who are using the current development train of NINA, version 1.11.

I've been working with another NINA contributor on a plugin for NINA's Advanced Sequencer that replaces the standard meridian flip trigger with a new one called Smart Meridian Flipper.

SMF can read in an APCC .mlm file or one in SMF's own obstruction definition format. It will then dynamically adjust the flip time based on the target's declination and what that corresponds with in the MLM file in terms of a meridian limit.

Flips will happen 10 seconds prior to the mount reaching the defined limit so as not to trigger an adverse reaction from APCC, which itself can be configured to do anything from emit a warning to halting tracking or parking the mount - the latter two being not-helpful when it comes to unattended imaging.

If you are a 1.11+Advanced Sequencer user, use (or aspire to use) meridian limits in APCC, and are interested in having your sequences' meridian flips take advantage of these limits and the wild and crazy world of counterweight-up imaging, I've made the plugin available to try out and test. It seems to work fine on my setup (MLM generated in APCC Pro, driving a Mach1+CP3) but I'm interested in seeing how it works for people who might not have the typical hourglass-shaped limits and perhaps something more funky or asymmetrical going on.

When you run a sequence, SMF will display two time values in its status area:

1. The local time when there would be a suspension of activity and tracking is halted before reaching the meridian if the limits dictate there will be a need for that
2. The local time when the flip will occur

I think in normal settings, most people will not have any need to pause on approach to the meridian so both times will be the same. That's fine. It just means you'll image straight through the meridian until the specified time, which is when the flip will happen. So if your target transits at 1am and it's at a declination that gives you 2 hours of room past the meridian, then the flip will happen at 3am (or really, 2:59:49, due to the 10 second buffer prior to hitting the limit.)

You can download the plugin here:

To install it:

1. Make sure you're running NINA 1.11 build 92
2. Create the folder %LOCALAPPDATA%\NINA\Plugins if it does not already exist
3. Unzip the download and drop the DLL file into the above folder, then start NINA

Once NINA is opened:

4. Go to Options > Plugins > SmartMeridianFlipper and configure it with the .mlm you want to use for your meridian limits.
5. Go to Options > Imaging > Meridian Flip Settings and change both Minutes After Meridian and Max. Minutes After Meridian to 1.
6. In the same section, make sure that Pause Before Meridian is 0
7. In your Advanced Sequencer sequence, *replace* any instance of the standard Meridian Flip trigger with the Smart Meridian Flipper trigger
8. Go about your business as you would normally do. If everything goes according to plan, you'll image right up until you hit the meridian limit (minus 10 seconds) for your target's declination.

The plugin system in NINA is being finalized in its design and there will be some major changes soon, so this specific plugin file that I linked above may not work in builds of 1.11 past the current build 92. It will be updated as the plugin system evolves over the next few weeks, which will include an automated way to download and update plugins as new versions are made available by their respective authors. I wanted to make this plugin available to interested persons early to get it some wider testing. Any testing and feedback is greatly appreciated, of course, and that feedback can be given directly to me ( or on the NINA Discord server.

A quick and dirty FAQ:

Q: Will I still have the standard Meridian Flip trigger available if I want to go back to using it?
A: Yes, it'll still be there. Drag SMF to the trash icon to remove it and drop the standard Meridian Flip trigger back in to your sequence in its place. Essentially the reverse of step 7 above.

Q: Will this be available for NINA 1.10?
A: No. This is a plugin and NINA's plugin system is new as of more recent builds of 1.11. 1.10 is in bug fix-only mode anyway

Q: Will I be able to use this in NINA 1.11's Simple Sequencer?
A: No. As with all plugins, this is available for use only within the Advanced Sequencer

Q: If I'm having a problem with this, what info do you need?
A: Your .mlm file and the target's declination would be great, otherwise I would have no way to replicate your conditions/configuration

A: ...

Thanks and happy imaging.


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