Using N.I.N.A. with Astro-Physics mounts

Introduction

This document is to serve as an explainer/FAQ for using N.I.N.A. with an Astro-Physics mount. While there is nothing specific to N.I.N.A. that one must set in the Astro-Physics ASCOM driver, APCC, or the mount’s Control Panel settings, there are a number of helpful configuration tips and capabilities within N.I.N.A. that will allow you to take full advantage of your Astro-Physics mount when used in conjunction with APCC (Astro-Physics Command Center) Standard or Pro.

This document assumes that the reader is using the following software:

Horizon limits

APCC allows you to set horizon limits for the mount. This prevents the mount from tracking below your local horizon where your view may be blocked by trees, houses, or other obstacles. APCC stores these horizon limits in a text file with a .hrz file extension. The format of the file is quite simple, with two columns of numbers:

As you can see, the first column is the true north azimuth in integer degrees and the second column is the angular altitude of sky obstructions at that azimuth. The altitude can be specified in either integer or decimal numbers. You are able to specify an altitude for each of the 360 degrees of azimuth around your mount, from 0 to 359 degrees. Altitudes do not need to be defined for every degree between 0 and 359. You can have gaps in azimuth where the last-defined altitude value is used for any subsequent missing azimuth degrees. This is helpful if you have a dome or large views of the sky that have the same altitude limit.

This same file can be used by N.I.N.A. to inform it of your local horizon. When configured with the location of the horizon limits file, N.I.N.A. will overlay the horizon on target information charts. You will also be able to use the horizon-related triggers in Advanced Sequencer. Doing so will allow you to start and end imaging when the target is truly visible. This solves the problem of ending up with a bunch of images of trees or the side of your house because your sequence started too early or ended too late. Configuring N.I.N.A. is simple:

  1. In N.I.N.A., specify the path to the .hrz horizon limits file under Options > General > Astrometry.
  2. In Advanced Sequencer, you can now use the the following two items:
    • Loop While Altitude Above Horizon – a loop condidtion that will keep a looping instruction set running while the target is above your defined horizon line. This is found in the Loop Condition category of instructions.
    • Wait Until Above Horizon – An instruction that will pause the sequence until the defined target is above the defined horizon line. Found in the Utilities category.

You would use both of the above instructions together. Wait Until Above Horizon is used to prevent your sequence from starting until the target is above the defined horizon line. Loop While Above Horizon is used to loop the instruction set until the target sets if a different loop condition doesn’t end the loop before it does.

A basic example of how to use horizon limits in Advanced Sequencer

Meridian limits

Meridian limits are a sort of complex topic. Realizing their benefit requires you to be well-aware of how mounts, especially equatorial mounts, work as well as the limitations around how they move when considering the physical dimensions of the telescope(s) they carry. Meridian limits are intended to prevent the telescope, usually the rear and western side of it, from tracking too far and crashing into the pier or tripod legs. They can also serve to define areas around the mount where the telescope can continue tracking past the meridian in a counterweight-up orientation for some amount of time without crashing.

APCC allows one to define meridian limits for their mount+telescope configuration using its built-in tool. Please refer to APCC’s documentation on meridian limits. Ray Gralak also has a video on this topic. When a meridian limit is defined in APCC, it is saved in a .mlm meridian limits definition file. The location of this file is usually in the C:\ProgramData\Astro-Physics\APCC\ folder.

Taking advantage of APCC’s meridian limits in N.I.N.A. requires the use of Francesco Meschia’s Smart Meridian Flip plugin for N.I.N.A. 1.11. The following steps should get it working:

  1. In N.I.N.A. 1.11, go to Plugins > Available and install Smart Meridian Flip. Restart N.I.N.A. to activate it.
  2. Go to Plugins > Installed, select Smart Meridian Flip, and specify the location of your APCC meridian limits (.mlm) file
  3. In Advanced Sequencer, replace any instance of the stock N.I.N.A. Meridian Flip trigger in your templates with Smart Meridian Flip. The trigger will be found under the Telescope category of instructions.
  4. You’re done!

Smart Meridian Flip will pause or flip the mount, whichever is appropriate, up to 10 seconds prior to reaching the limit. This is so that the limit is not actually reached and APCC reacts by stopping tracking or parking the mount, which can mean an end to your session. A flip can happen early if you are doing 5-minute exposures and there is only 4 minutes of time before the limit minus 10 seconds is reached.

Below is a short video that demonstrates how this works.

Point mapping

Compared to APCC Standard, APCC Pro adds point and tracking modeling via its APPM (Astro-Physics Point Mapper) facility. This has many benefits for guiding during imaging and is certainly required if you intend to do long exposures without guiding. The premise is that there are many factors that affect how our telescopes perform, from mechanical to atmospheric, and mount tracking and pointing can be further improved if these various factors can be found and compensated for.

APPM builds a model by pointing the telescope at many points around the sky and plate solving each point. It then compares what it thinks the RA and declination are to the RA and declination that the plate solver reports. Any differences are noted and accounted for, which allows APPM to build a model. The more points that are taken, the more detailed the model is.

How often this modeling should be done will vary with your type of setup and the local conditions. A model can be used for some time – weeks or even months – if you are operating from a permanent observatory. Mobile imagers will want to build a new model in the places they set up. Some people prefer to make new models often, ranging from once a week to nightly. How often really depends on the situation.

To assist with model creation for N.I.N.A. users, I have created the Utilities for Astro-Physics Mounts plugin for Advanced Sequencer that works with APCC Pro 1.9. It implements a sequence instruction that you can use to automatically run an APPM mapping session directly as a part of your sequence, such as at the beginning of the night. Please head over to its page for instructions on how to use it.

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