Mimir - Focus Information

The focus mechanism on the Perkins telescope moves the secondary by 1 inch for every 9600 motor steps commanded to it, and a positive step change moves the secondary away from the primary. Details of the focus gear system are on this link.

Focus scans were done with Mimir in the F/5 and F/17 cameras on the 12/2004 engineering run. The results are in plots and tables below. Note that use of the J-band corrector moves the focus closer to the K-band value. Also note that the F/5 and F/17 cameras exhibit about the same focus in K-band, only. Refocus will be necessary when changing bands, cameras, and as the temperature changes in a night.

Relative Focus Shifts to Nominal Focus
Band
F/5 Relative Focus Shift
F/17 Relative Focus Shift
J-Band + J-Corrector
+36
-53
J-Band (alone)
-32
-198
H-Band
-4
+43
K-Band
0 (reference)
-60

Focus Scan Plots:

F/5 Focus Scan - Click on small image to see full sized plot

F/17 Focus Scan - Click on small image to see full sized plot