The Mosaic 1.1 Imager is populated with thinned, AR coated e2v CCDs. The CCDs are a "deep depletion"
variant from e2v for improved red response. A "2-layer" AR coating was chosen for improved blue response
relative to the SITe chips used in the previous Mosaic imagers, giving a big advantage in overall exposure
time, about 30% shorter for equal S/N in U band. Additionally, the 2-layer coating provides a more uniform
depth in all bands (generally limited by U and B) and has a flatter response curve to allow easier
photometric transformations. The figure below shows the e2v QE
performance relative to the typical SITe CCD previously used in
Mosaic 1. The tables below, reproduced from version 4.0 of the
manual, provide additional information regarding the read noise,
gain, and other properties of the e2v CCDs.
Typical flat-field image (R-band). This raw image shows the good cosmetics and uniform response and sensitivity of the devices. The "rolled-off" edges are caused by filter vignetting.