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Pixel scales and FOV

Pixel Scales1 and Field of View2

Camera Pixel dimension (arc sec) Field of View (arc sec)
f/6 0.1171 119.9 x 119.9
f/14 0.0499 51.1 x 51.1
f/32 0.0219 22.4 x 22.4
f/32 + Altair Field Lens 0.0214 21.9 x 21.9

1NIRI with Altair has been measured to have radial barrel distortion at f/32.  This is most prominent for programs performing large offsets.  The formula for removing the distortion is r' = r + k*r*r, where k = (1.32 ± 0.02) * 10^-5 . r is the uncorrected distance from the field center in pixels and r' is the corrected distance from the center in pixels.  Thus, at a distance of 500 pixels from center, an object will appear about k*500*500 = 3 pixels closer to the center of the array than reality. This correction is available in an IDL program, and PIs interested in high-precision astrometry are encouraged to contact either the NIRI or Altair instrument scientists to discuss this issue.

2For full (1024 x 1024) array