To take sky flats:
1. Take sky flats if the sky is clear.
Sky flats when it is cloudy are no good.
The telescope is open and pointed towards zenith.
2. Wait for the sky to get dark enough:
To monitor the sky brightness,
put
Camera Wheel N 3.75
Grating Unit: Mirror
FW1 =Br_gam
FW2 = Clear
Mask to use: NO MASK
Mask to position: NO MASK IN USE
Remember to hit COMMIT INSTRUMENT SET UP after changing filters, etc.
in readout manager gui, change
SAVE IMAGE to
MANUAL <--- not saving
DIT = 2 (2 second exposures)
Set
No. exposures = 100
hit
SET NEW VALUES
hit
START READ
This will start a stream of exposures.The images are displayed in the small Lucifer display window.
Put the cursor in the window and look at the counts.
When the counts in the Br-gam filter are about 1500, then the counts in
Ks will be about 15000 and it's ok to start.
Hit
ABORT to stop the exposures.
3. Take Ks flats
FW1 to
clear
FW2 to
Ks
************* MAKE SURE YOU NEVER HAVE FW1=clear and FW2=clear at the same time
***********
Start 100 exposures with the Ks filter to verify that the counts are OK; (like DIT=3, counts are 16,000)
ABORT.
set
SAVE IMAGE to
AUTOMATIC
FRAME TYPE = FLAT
# Exposures = 10
SET NEW VALUES
START READ
This takes 10 sky frames.
4. Take H-band flats
Monitor the sky brightness with the
FeII filter, instead of the Br gamma,
Repeat as in Steps 2 and 3.
H sky counts will be about 10x the
FeII filter counts.
For H and J, take a set of short flats and a set of long flats
5. J-band flats can be taken as soon as the H band flats are done.
No need to do monitoring.
J. Bechtold, F. Bian Jan 2010, May 2011