Comment Technical Corrections (Score 1) 95
The optical observations of the UDF from 2004 were conducted with the Advanced Camera for Surveys/Wide Field Channel (ACS/WFC) not the predecessor to WFC3 (Wide Field/Planetary Camera 2, or WF/PC2). Also, the optical channel of WFC3 does offer a small improvement in pixel scale (40 milliarcseconds/pixel, versus 50 mas/pix for ACS/WFC. However, the near-infrared channel (where these images were taken) only has a pixel scale of 130 mas/pix, a factor of ~2.5 worse than ACS/WFC.
(The diffraction limit of HST varies from ~50 mas at 500 nm to ~150 mas at 1.5 microns, so the native resolution is worse as well. However, undersampling of images due to the detectors' oversized pixels is what dominates the fine details of its effective resolution. The true resolution is actually hard to estimate offhand for images like this. Each observation occurs with sub-pixel offsets with respect to the others, so if you subsample and stack them, you can recover much of the resolution that was lost due to undersampling. With many orbits' worth of images contributing to the UDF, they might have gotten back all of the lost resolution.)
(The diffraction limit of HST varies from ~50 mas at 500 nm to ~150 mas at 1.5 microns, so the native resolution is worse as well. However, undersampling of images due to the detectors' oversized pixels is what dominates the fine details of its effective resolution. The true resolution is actually hard to estimate offhand for images like this. Each observation occurs with sub-pixel offsets with respect to the others, so if you subsample and stack them, you can recover much of the resolution that was lost due to undersampling. With many orbits' worth of images contributing to the UDF, they might have gotten back all of the lost resolution.)
