astropy
Strange negative patterns in the ePSFs
Hello,
Thank you for creating this great package as it has been quite easy to use s far. I have been having some troubles understanding the hashed structure seen in the ePSFs. I find great PSFs (oversampling=1) for both space-based and ground-based images. However, as soon as I increase the oversampling, this grid pattern occurs and has this negative grid that appears and this effect increases with increasing the oversampling. It's harder to tell from the oversampling=5 ground based image but it is there. Can someone please help me understand this? Thanks
Had similar issue when I was preparing the lecture note for this spring's TA note (this note):
(In the note, I didn't strictly followed Stetson's original PSF extraction technique. Now I think I should've followed the Gaussian + spline technique, but anyway I extracted the PSF without Gaussian component, i.e., pure spline interpolation).
When I tested, smaller number of iteration (for epsf in photutils) gave more severe such patterns. Then I just increased the number to 100 and it got better. The "strange patterns" then appeared only at the outskirt of the PSF, so I thought maybe it's not a big problem. I don't quite understand the theory of ePSF, so sorry I can't give meaningful discussion right now...
@gkacprzak - we think #974 should have solved the problem. Can you give the latest development build of photutils a try? (Or if you aren't set up to install from source, try it when 0.7.2 comes out.) If that addresses your problems here, we can close this issue.
@ysBach - it's less clear to me if your problem is the same as what #974 fixed. Can you give the latest master a try and hopefully that will determine if it's the same or a different issue?
