detector plane sampling rate 2x expectation

[LouisDesdoigts]

The detector plane sampling rate that is input to an optical system through osys.add_detector(pixelscale=arcsec_per_pixel) returns actual sampling rates at twice that input to the system. This corresponds to an equivalent pixel size half that of what is expected.

Presumably there is a factor of 2 or 0.5 in the code that should not be.