Combining data from two scopes creating strange borders

Bruce Donzanti

I have done this in the past with a friend but this time we are having a strange problem.  I have data from a Tak FSQ 85-EDX and my friend from a WO 132mm Fluorostar.  We are both using the same camera (ASI6200mm) but mine is a very wide filed and his relatively small. So, I calibrated my frames and sent them to him, and he calibrated his data separately before using WBPP to combine them.  The result was these strange edges with distorted stars (see attachment).  However, when testing each dataset separately, the images appeared but my friend's data did have some stars distorted along the edges.  So, he cropped those out before combining but the strange edging reappeared.  When I did a complete WBPP run (meaning, calibration, registration, and integration) just on my data, the image was fine.  Any idea what is causing this and if can be corrected?

BlockHead

This is because of the normalization between the frames. The sky values between the frames will not match perfectly. In addition the edges will have rejection so it will have a ragged edge as you have shown. Although you are using the same cameras- there can also be differences in gain values that will not be compensated for when doing this simple method of combining. This is an advanced thing to do (well) and requires a little planning an math. 

It might be sense to simply do an overlay rather than combining the discordant data. You would use linear fit in the simplest attempt- but I suspect NSG for normalization might be better- and perhaps Photometric Mosaic could be employed in some clever way. John Murphy would probably know.

Once I have the notification aspect of this forum working...I will ping @JohnMurphy  <--- that is not working right now... but I am hoping to have it work soon.

-the Blockhead