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The SUBARRAY_DITHER primary dither pattern was created before the start of Cycle 1 to increase the overlapping spatial coverage between the long and the short wavelength SUB64P subarrays, which are observed simultaneously. The SW SUB64P subarray is only 2" wide. The intent was to ensure that the target was observed in either channel for at least a subset of the 4 maximum allowed number of dithers. Prior to launch, the NIRCam team worked with the upper bound on the JWST required pointing performance of 1". However, commissioning results demonstrated that the pointing performance greatly exceeds requirements, with a typical pointing accuracy of 0.1" (1-σ radial, Rigby et al., 2022).
Moreover, during launch, the first fold mirror in the NIRCam short wavelength channel on module B underwent a very small motion (expected from ground tests) which serendipitously improved the overlap between the short and long wavelength channels. In addition, the NIRCam team redefined the spatial location of the SUB64P subarray (and the SUB160P as well) on the B1 and B5 detectors, to make them concentric.
For all the reasons above, the usefulness of the SUBARRAY_DITHER primary dither pattern is greatly reduced, and this type of dither may be discontinued in the future. Currently, the dither pattern is still offered, but the NIRCam team recommends using the subpixel dither type STANDARD pattern instead, to better sample the PSF while still mitigating detector defects.