1997PASP..109..130M

A unique focal reducer for the Steward Observatory 2.3 m Ritchey-Chretien telescope on Kitt Peak was designed and built. It increased the field of view and a Loral 2048 X 2048 charged couple device (CCD) with 15 mu m pixels from about 5' x 5' to 24` x 24`. The inverted-Cassegrainian, two-mirror design permits high efficiency of UV wavelengths and good broad band image quality from 3500 A to 8500 A without significant chromatic aberrations. Other features include a coronagraph and a filter slide in the slow f/9 beam which achieves the difficult and useful combination of narrow band imaging with a wide field of view. THe filter slide tilts to vary the center wavelength of narrow interference filters to accommodate different red shifts. The image quality is seeing-limited in the central 12' diameter, and degraded by about 0.8" in the central 18' diameter, and degraded by 1-2" at the edges of the field. The development of hte optical system prescription is briefly discussed. The instrument is used to obtain continuum-corrected H-alpha and [S II] images of the edge-on galaxies NGC 4244 and NGC 5907. Interesting filamentary structure is evident. THe distribution of ionized hydrogen gas in NGC 4244 and NGC 5907 is quantified. THe data indicates those galaxies do not have an extended halo like that in NGC 891 and our Galaxy.