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:

Grating Mode Camera
Temp (C)
Focus
400 M1 19 -300
400 M1 16 -600
400 M1 13 -660
400 (+GG455) M2 19 -990
400 (+GG455) M2 16 -1200
400 (+GG455) M2 11 -1300
400 M2 16 -250
400 M2 11 -690
600red (+GG385) Mid 17 -1770
600red (+GG495) Red 17 -992
600old (+GG385) Mid 15 -1540
1200 M2 17 -700
1800 @700nm 13 -825
1800 @660nm 19 -460
2100 @650nm 16 -200
2100 @650nm 13 -555
2100 @650nm 17 -376

 

Blue Camera spectroscopic focus values:

Grating Mode Camera
Temp (C)
Focus
400 M1 17 1615
400 M1 11 1320
400 (+GG455) M2 11 773
600blue UV 17 1650
600blue Blue 17 1650
600old UV 11 1370
600old Blue 11 1440
600old (+GG385) Mid 11 880
600old (+GG495) Red 11 1350
600blue (+GG385) Mid 17 820
600blue (+GG495) Red 17 1650

 

Red Camera imaging focus values:

Filter Lamps/(%) Exp
(s)
Camera
Temp (C)
Focus
None Dome/5 0.5 10 -1130
B Quartz/50 2 19 -715
V Dome/20 0.5 10 -580
R Quartz/50 1 19 -1320
VR Dome/25 0.5 16 -470
VR Dome/25 0.5 11 -814
SDSS-u Dome/20 1 10  
SDSS-g Dome/20 1 10  
SDSS-r Dome/20 1 10 -700
SDSS-i Dome/20 1 10 -900
SDSS-z Dome/20 1 10 -1250
  Dome/20 1 10  

 

Blue Camera imaging focus values:

Filter Lamps (%) Exp
(s)
Camera
Temp (C)
Focus
SDSS-g Quartz/50 4 11 1100
SDSS-r Quartz/50 1 11 990
SDSS-i Quartz/50 0.3 11 860
SDSS-z Quartz/50 0.5 11 540