Performance of the multiple mirror telescope (mmt) vii. Image shrinking in sub-arc second seeing at the mmt and 2.3m telescopes

Observations of image size and motion have been made at the MMT and 2.3m telescopes. At the 2.3m, simultaneous observations were made of image size and position at 0.8μ and various IR wavelengths. The MMT observations were all at 0.6μ, and were used to measure the isoplanicity of the atmosphere for image motion, the time development of image position, and the telescope to telescope correlation of image motion. At both telescopes the image size was larger than expected for the image motion. The MMT results showed that although there is a finite outer scale of turbulence for the atmosphere, it did not appreciably reduce image motion. Therefore the excess image size is caused by excess small scale turbulence (presumably inside the dome), together with various telescope imperfections. It is inferred that sub-arc second seeing is frequently available at both Mt. Hopkins and Kitt Peak, but that the image is substantially deteriorated in the observations. While correction for image motion is a necessary nart of a program to shrink telescopic images, there are other high priority cures also needed.