Goodman Spectrograph Typical Focus Values

Updated 3 Jun 2021

Here we provide typical focus values for the Goodman instrument. The instrument focus is usually set once per night, and is done as the first step before afternoon calibrations. Note that the focus is dependent on ambient temperature, so values will change significantly from summer to winter, in fact, variations of up to ~500 units could happen from one observing run to another. Also, the depth of focus is roughly 100 units, so focus values within +/- 50 units can be considered consistent with no focus difference.
The BLUE camera focus values should be mostly positive; RED camera focus values are mostly negative.

See how to perform a spectroscopic focus measurement.

See how to perform an imaging focus measurement.

The following values are representative. In some cases we provide actual measured values obtained on different dates to illustrate the variations; both blue and red cameras are affected by focus variations as a function of temperature. You should perform a focus sequence every afternoon.

Red Camera spectroscopic focus values:

Blue Camera spectroscopic focus values:

Red Camera imaging focus values:

Blue Camera imaging focus values: