Bill Hoffmann, Phil Hinz
June 13, 2000

The accompanying movie is a record of the opening of the MMT building shutter obtained with the nulling interferometer, BLINC, in its imaging mode and the mid-infrared camera, MIRAC, used with its pupil imaging lens. In this mode the MIRAC cold stop and the telescope aperture are imaged onto the 128x128 Boeing Si:As HF-16 array. The images have been processed with a bad pixel mask, a subtracted dark image to remove pixel offsets, and a multiplicative gain matrix to remove sensitivity variations over the array. In these images, increasing elevation on the sky is up and increasing azimuth is to the right. The images were taken at a rate of approximately one per 1.33 seconds.

The images were obtained with the MMT f/9 secondary which is oversized relative to the primary mirror and is mounted in a ring of greater diameter than the secondary. The BLINC cold stop, designed to mask the secondary spider and obscuration, was left out for these observations. The images view via the oversized secondary mirror the primary mirror with its ambient temperature central Cassigrain hole and periphery and the secondary structure and spider as reflected in the primary mirror.

The first images of the movie (see below) show the bright shutter against the cold stop. The image of the cold stop is larger than the array and offset toward the lower left so that the cold stop appears only in three corners of the image. The central hole and periphery of the primary and spider do not show because they are at the same temperature as the shutter. The last two images show the shutter fully open. The telescope aperture is offset toward the lower right relative to the cold stop so that the right side of the telescope aperture is vignetted by the cold stop. Hence the hot surrounding of the primary mirror shows only at the left two corners. The bright central disk is the hole in the primary. The ring around the secondary and spider are seen in reflection by the primary as is the sky whose low flux results from a combination of the thermal radiation from the relatively low emissivity of the earth's atmosphere, the two telescope mirrors, and the warm entrance window to the instrument.

Last update: 2000/08/11
William Hoffmann