Nominal zeropoints for a 5 arcsecond aperture at an airmass of 1.0 are given below. A larger field stop was installed in February 2003 leading to less vignetting at L’ and M’, and larger zeropoints. An ARC controller with a different gain was installed in Oct. 2006, resulting in a difference in zero points. Note that the zeropoint is a function of airmass, can vary from night to night, and will be smaller than these values if the seeing is very poor.
|Oct 2002 – Feb 2003||Mar 2003 – Oct 2006|
Larger Field Stop
|29 Oct 2006 – May 2008|
|June 2008 – Present |
(row-reset in thermal)