DIS SLIT WITH OCCULTING BAR A 1.2 arc second slit with a 2 arc second occulting bar is available for DIS. This slit is narrower than the others so you might consider it even if you don't need the occulting bar. FLAWS This slit was made to test a new cutting technique. Because we used a rejected slit blank it has the following flaws: 1. One corner of the plate is unpolished and non-reflective. This is probably not of practical importance; the central 2-3 arc minute diameter region is good. Stars will "disappear" when they move into the bad corner, however. 2. Cosmetic imperfections. There are scratches on the surface. I believe neither flaw will interfere with typical use. Only the slitviewer image is affected. The spectrograph sees an excellent slit with no compromises on science data. WARNINGS The occulting bar is at field center. Remember this when using the slitviewer software to center an object because the default will put your object on the occulting bar. Russet McMillan says "Anyone using the centering offsets recommended by slitview will need to CHANGE the recommended X offset by several arcseconds to keep their target out from under the bar." Unless, of course, you want that object blocked. The current DIS configuration, with the original cameras and blue Tektronix and red Texas Instruments CCDs, has pixel scales of 1.1 arc seconds per pixel in the blue and 0.61 arc seconds per pixel in the red. This new 1.2 arc second slit is undersampled in the blue. On the red side, DIS images of a star in the slit show adequate (just) sampling. Scattered light performance is unknown. In particular, we don't know how much light from a bright star on the occulting bar will get into the spectrograph at large field angles. I worry about reflections and scattering off the guider camera and its mirrors and filters. Alan Uomoto October 3, 2001 APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 527 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO