Like so many other wavelength dependent instrument properties, field of view varies widely between optical, near, and mid-infrared instruments. As seen in Figure 5, there is an enormous range of fields that instruments cover but invariably the smallest field instruments operate at either mid-infrared wavelengths or use AO systems. in fact there is a fairly staggering factor of ~108 between the largest field optical imagers planned and the smallest imagers currently in use. For mid-infrared systems, this is primarily driven by the small mid-infrared detectors presently available, though there are ancillary reasons like the maximum practical chop-throw possible with the large secondary mirrors needed on 8-10 m class telescopes. Again, AO imagers must use extremely fine plate scales to adequately sample an AO corrected focal plane, and hence tend to have small fields when the maximum size NIR detector has been (until recently) 10242.
In the middle of the pack, large field mosaic based near-infrared imagers are now coming on-line. While small compared to the largest field optical imagers, this next-generation of imagers will enable important new scientific frontiers with wide and deep surveys (see Sec. 4 for details). The high end in Figure 5 is defined by wide field optical imagers that are becoming increasingly popular, including on telescopes too small to be included in this survey. For example, wide field imagers like ESO's OmegaCAM and WFI and University of Hawaii Institute for Astronomy's Pan-STARRS, represent state-of-the-art optical imagers.
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