8 Image quality becomes worse after taking some exposures

Masao mentioned to me that during the SN observing, they noticed that the image quality become worse and worse in a sequence of exposures. I analyzed the most recent such sequence of z band exposures Masao pointed me to. They are taken on 12/15/2012, 161515-161525.

Here is a summary of the Image quality measures for these exposures. As you can see, the e1 and e2 keeping increasing/decreasing from 0 as the sequence goes, indicating that the tracking/guiding errors are increasingly worse. So, there must be some problems with the guiding/tracking when taking a series of images. The image whisker analysis shows that there are 300 - 400 microns x/y decenters on the optics system among these exposures. See the attached pdf file for more details.

  • exposure: 161525