High Resolution Echelle Spectrometer     Telescope Focus With HIRES

Observers with no prior experience at Keck may wonder who focusses the telescope and how. For many of the instruments at Keck, there is a procedure called MIRA which not only checks what we normally think of as focus, but can also correct secondary tilt and the alignment of primary mirror segments with respect to each other (stack). MIRA is run by the observing assistant. Unfortunately, MIRA can not be run with HIRES. The field of view of the guider is too small to capture the images necessary. Instead, your observing assistant will run a procedure called autofoc. This procedure will correct for telescope focus but not secondary tilt or stack. Since autofoc is incapable of correcting for secondary tilt (and HIRES is on axis anyway) there is no reason to run it to correct for coma at different PA's the way observers used to some other instruments may be inclined to do.

Normally, autofoc is run at the beginning of the night. Your observing assistant will monitor a number of telescope and environmental variables during the night and may advise you that another autofoc would be useful. Observers are also free to request an autofoc at any time as well. If you notice (for example) that images on the guider are looking a little worse, or that the width of spectra has increased it may be a sign that autofoc should be re-run.

Contacts at Keck for HIRES are     (primary),     (secondary).