Characterize PSF using out-of-focus images

Measure the optical aberrations of individual exposures of PFS data from out-of-focus images.

The current plan is to follow the procedure by Joshua Mayers which was used for HSC images (e.g., https://jira.lsstcorp.org/browse/DM-8565 and connected tickets). This means forward modeling of the PFS images taken at LAM with Galsim.

I am documenting my progress at https://github.com/nevencaplar/PFS_Work_In_Progress/blob/master/Zernike.ipynb.

Update: July 5, 2018, report: https://www.overleaf.com/17550215gqrxkdfywqkp#/66627172/