IRAC Instrument Handbook - IRSA - California Institute of Technology

IRAC Instrument Handbook
Figure 2.5. Optical i mage distorti on in IRAC channels. The panels show the image distortions as calculated
from a quadratic pol ynomial model that has been fit to in-flight data. The magnitude of the distortion and
the direction to which objects have moved from their ideal tangential plane projected positions is shown with
arrows. The length of the arrows has been increased by a factor of ten for cl arity. The maxi mum positional
deviations across the arrays for this quadratic distortion model are less than 1.3, 1.6, 1.4 and 2.2 pixels for
channels 1−4, respectively. The derivation of the pixel scales that are listed in Table 2.1 fully accounted for
the quadratic distortion effects shown here.
2.2.4 Distortion
Due to the off-axis placement of IRAC in the Spitzer focal plane, there is a small amount of distortion
over the IRAC FOV. The maximum distortion in each IRAC band is < 2.2 pixels (compared to a perfectly
regular grid) over the full FOV. Figure 2.5 shows the distortion across all four IRAC channels, as
determined from data taken during IOC/SV.
Instrument Description 10 Description of Optics