Figure 2a. This figure shows the spherical aberration measured on the 3.5m telescope as a function of telescope altitude measured on August 14, 2000. No variation of spherical aberration is seen as a function of telescope altitude. The mean of 0.14" is quite low in comparison with other aberrations. The deviation of only 0.016" is a somewhat lower than what is normally seen.

Figure 2b. This figure shows the spherical aberrations measured on August 15. As on August 14, no variations are seen with telescope altitude. The scatter in these measurements is more typical of what normally seen in the Shack-Hartmann measurements.

Note, that the mean spherical aberration at the time of these measurements is 3.4 times the value seen on August 14! This effect is real and is related to the fact that the mirrors were still in the process of cooling down to equilibrium when these data were acquired. At the time of these measurements, spherical aberration was dominating the image quality of the telescope. Its likely that this would NOT have been the case if these measurements had been made several hours later in the evening. Its also possible that the small scatter seen in the August 14 data is related to the fact that the telescope was truly at thermal equilibrium at the time of those measurements. During the August 14 measurements the truss and both mirrors were cooling at rates of less than -0.2 C/hr. During the August 15 measurements the cooling rates were all on the order of - 1.2 C/hr.