The F28X50OIII mode is useful for narrow-band imaging of O III 5007 Å. The narrow bandpass and high spatial resolution provides some advantages over WFPC2 with the F502N filter, although the spatial resolution is not as high as that of ACS/HRC with its F502N filter.
This filter has a significant red leak longward of 1 micron. Depending on the source spectrum, the contribution from redleak may swamp the contribution from line emission.