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Plate solving using AstroTortilla and SharpCap

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Plate solving is the action of resolving what you see in the sky to match where your (computer controlled) mount thinks it is in the sky. For those transitioning from using a handset to computer controlled, see this step as being roughly the same topic as a 1-star align: validating the position of where your mount is pointing so that you can have the confidence that when you slew around to another object, it will be centered in view.

Various programs exist that will do plate solving. For this I’ll be explaining using AstroTortilla that does the plate solving, and SharpCap to do the imaging of the night sky that then gets fed to AstroTortilla, and Cartes du Ciel for the navigation of the sky.

What You Need

How To Do It

  1. First download AstroTortilla (https://sourceforge.net/p/astrotortilla/home/Home/). and follow the install procedure.
  2. In SharpCap choose the File menu then select SharpCap Settings… Plate Solving.
  3. In the Path to “solve-field” tool entry (which should be auto detected in SharpCap) make sure it says c:\cygwin\bin\solve-field if you went for the defaults for your AstroTortilla installation.
  4. I have “Automatically downsample large images when solving” and have –sigma set to 20 but I’ve had to tweak these settings now and again if it fails to solve.sharpcap_platesolving
  5. In CDC, slew to an object. You’ll have an idea if this is good enough and where you expect…
    Tip: I have my camera set to do a 2 second exposure for focusing for this beginning part of my setup process and choose a familiar object or area in the sky so you can visually look at where your scope is roughly pointing is correct.
  6. Back in SharpCap I ensure my EQMOD mount is connected. If not, go to File… Hardware and under Mounts, select your EQMOD profile.sharpcap_hardware
  7. You will have a control appear in SharpCap now on the right side that allows you to control your mount. Ensure it is connected.
  8. When you’re happy that there are some good stars in your view, take a 15-30 second exposure. This should show more detail and give you some confidence that the plate solving should know where it is in the sky.
  9. I now press the target looking symbol on the mount controls in SharpCap (bottom left symbol). This instigates the Plate Solving. It will wait for a capture to finish then send it to AstroTortilla. If all is good, the top bar will turn green and will tell your mount where it is. If it turns orange, read the suggested instructions on how to adjust the settings (in step 4) to get it to solve for you.

What We Did

Plate solving takes a capture image of the night sky and attempts to work out, from the position of the stars, where your mount is actually pointing. To do this with our setup, we are using an correctly set up EQMOD controlled mount.

These blog posts will take you through the following:

  1. Set up and polar align your mount correctly
  2. Configure your mount with EQMOD
  3. Balancing your scopes correctly
  4. Connecting CDC to your Mount using EQMOD

We then use SharpCap for image capturing, which has AstroTortilla configured in its Plate Solving settings. SharpCap will capture an image, and send it to AstroTortilla. If all is good, your image will be resolved and any nudges needed to your mount to position so it is sync’d correctly with CDC will occur.

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