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