Wednesday, August 15, 2012

First look at image quality

On Monday night, Daniel took a 200 second guided exposure in the r' band that he noted had stellar images with FWHM about 0.6 arcseconds.  This is the best we have seen so far, and so I took some time to examine the images in a bit more detail.  I measured the FWHM of a dozen or so stars in each OTA, and I found that the image quality was good and quite uniform over the entire field.  The picture shows the measured average (in arcsecs) in each OTA.  I did not notice any significant departure from roundness in any of the OTAs. 

The worst FWHM, 0.615 arcseconds corresponds to an additional contribution of 0.22 arcseconds (in quadrature) over the best FWHM.  Also, the OTA with the worst FWHM, OTA 55, failed its metrology test - that is, it is not within the specs for final height of the detector plus package.  Thus, part of the poorer image quality might be a focus effect, though it is not much worse than the OTAs around it.  Finally, I note that we have not yet begun to adjust the telescope optics to optimize image quality over the wide field; that is an activity planned for early September.

All in all, it looks like pODI (and later, ODI) will have the ability to deliver quite good images over its entire field of view.


No comments:

Post a Comment