The extinction plots presented here represent nights over there course of generating the input catalog where photometric conditions were at their absolute best. By inspecting the diagnostic plots for each night of observations included in the catalog, the nights with perfect conditions, observations over a large airmass range (typically from AM=1.8 to AM-1.1 and sometimes greater) and a RMS fit better than 0.01 magnitudes were collected.
first set of plots are the zero-point values by filter. These plots represent three different cameras, each with a differing sensitivity across the spectrum. The first camera used (4shooter) is only present here as the first two points in the plots. The second camera (minicam) came into use in the middle of 2004. It was used extensively until the summer of 2005 when the Input Catalog production camera (KeplerCam) came online.
Of interest to note, the primary mirror in the 1.2-m telescope was re-aluminized during the summer break of 2004 and 2006 (and again summer of 2008). There is not a noticeable change in the instrumental zero point as a results of mirror re-coating.
The second set of plots are the atmospheric extinction constants measured for this set of excellent nights. The extinction values remain quite stable over the four years of the project. There is a slight change in the values when comparing observations made before and after the summer shutdown. The scatter in the fall values are also somewhat smaller (seen most clearly in the r filter).
Finally, the extinction values for these good nights are all plotted against the central wavelength for each filter. The coefficients are generally well behaved, though the presence of a gray term when comparing one session to another is apparent. The scatter in the z band values may be do to changing water vapor column density above the observatory from night to night.