What the Heck is Platesolving?

 

V1.5.3

On the ASIAir, platesolving is the process used to determine where the exact center of the image is pointing.  The process involves taking a preview image and clicking the plate solve button.  This starts a comparison process of “plates” stored on the ASIAir.  It doesn't need the internet to do so.  Once the solve has completed you will be presented with some options to sync or sync and goto.  Sync will just update the ASIAir so that it now knows exactly where the scope is pointed.  The next goto should get your object centered perfectly.  Sync will also update the position in Skysafari if you have that integration set up.  Sync and goto will just update the current location and then readjust the scope position to center the chosen object.

There is a limit to what ASIAir can platesolve.  The original ASIAir has a 0.4 degree limit which means the field of view along the short side of sensor must be greater than 0.4 degrees.  With the ASIAir Pro the limit is 0.2 degrees.   There are tools out on the internet to calculate the sensor field of view and this can also be done in Skysafari once your equipment and observing view are selected. It also cannot platesolve within 6 degrees of the pole.  However, the polar alignment tool can.

Other factors that can affect platesolve are not enough stars to match the plates or too many stars, too much math for the process to complete.  I have found that on average 200-600 stars seems to work well.  Adjust your exposure to increase or decrease the number of stars.

Its also important to get the main camera focal length precise.  Fortunately ASIAir has a great way to do this. Just enter “0” for the main camera focal length and it will calculate the focal length for you based on the camera used when you plate solve next time.

 Also note that you can do this with your guide scope as well if the field of view falls within the plate solve limits. Just temporarily turn off the main and guide cam in the app and then select your guide cam for the main camera.  Then enter “0” and do a plate solve.  Note the calculated focal length.  Swap the cameras back and enter the new focal length into the guide camera settings.  This will ensure your guide graph and rms error numbers are precise. 

There are a number of areas that ASIAir uses platesolving to get things on track.  One is called Goto Autocenter which will solve and reposition the scope to automatically center the object.  On the same screen you can preset the Center Exposure Time to use during this process.  Trial and error will determine which is best for your setup.  Without filters one or two seconds should be enough.  With narrowband filters this could go up to the Max depending on the filter used.  Its also useful if you have automeridian flip enabled.  After a flip the mechanics can cause the scope to be off and the autocentering allows the object to be recentered.

You can now also do a goto on a previously taken image and after a plate solve and recenter, allows you to resume a session on another day with minimal framing loss.

All of these features and enhancements will eventually lead to automated multitarget sequencing and hopeful some form of mosaic planning.  Its not there yet but you can see where all of this helps with that.

So what happens when you use filters?  For most light filters such as LRGB there is not much difference in star intensity.  When you use narrow or broadband filters they are so dense that you have to increase your exposures to record enough stars.  Usually 5 to 10 seconds will be enough depending on your scope and filter used.

Platesolving is key to successful use of many functions in ASIAir and totally negates the need for a finder scope.  The plates used to compare to your image are built into the product and it does not require internet access.  The exact location of where your scope is pointing can be completed in seconds and allows your gotos to center the object perfectly.