I took a risk up at Columbia's Pizza Lunch forum by talking about the Kepler flat-field. I also was exceedingly rude and talked through Price-Whelan's spot (he was supposed to follow me). I apologize! Well, you can't say I didn't try to bore the pants off of everyone: I talked about the (novel, and exciting to almost no-one other than me) result, published in our white paper, that it is possible to infer the properties of the flat field at higher than pixel resolution.
That is, the team (meaning, in this case, Lang) made simulated data with drifting stars, a PSF that varies slowly with position (and is well understood), and no prior knowledge about how the stars in the field are drifting. We find (meaning Lang finds) that he can simultaneously figure out the pointing of the satellite and the flat-field, even when the flat-field is both created and fit with models that have multiple sub-pixels per pixel. The reason it works is that as the star moves, it illuminates each pixel differently, and is therefore differently sensitive to the different parts of each pixel. It is not clear yet whether we can do this accurately enough to recover the Kepler sub-pixel flat-field, but damn I want to try. Unfortunately, we need lots of data taken in the two-wheel mode, and (as far as I know) they aren't yet taking any new data. Kepler: Please?