How to observe with the diffusers

First decide which diffuser to use and where to install it, whether FASU A or B, note the differently diffused PSF and FWHM implied, see table.

The diffusers are already mounted in FASU filter holders. Find them in the their drawer on the wall in the electronics room, next to the grism cabinet.
Install the selected diffuser in a slot in either the FASU A or B wheel.

Twilight flats

The commands below are given for Diffuser#1 (664) and i#12 filter.

wheels -d 664 -f 12 ; focus-offset
easyflat 3

Observations of target

Since there are no OBs, and if this is partial service night, you can block off this time in Visplot.

If observations are time-critical, start 10 minutes before to be sure you have time to point to target and possibly adjust the target's and standard stars' placement on the CCD, potentially window size etc.

In the commands below it is assumed using Diffuser#1 and filter i#12 observing object TOI.

tcs.setup-tel-alfosc if not already done
Make sure the ADC or the polarimeter retarder plate is out of the beam.
- alfosc.carriage out
- tcs.adc-arm-out
wheels -d 664 -f 12 ; focus-offset

tcs.append-object TOI 10 10 10.00 +10 00 00.0 2000.0 0.00 0.00 10.0
tcs.guide-object TOI
When autoguiding is ok, take test exposures to determine exposure time to use and possibly change the position of target on the detector:
- resetxy sets the CCD to full frame, no binning, default read speed
- exp 10 takes a 10 second exposure
- teloffset 10 0 moves the target 10" in positive X-direction.
- If you need windowing and/or binning follow the order in the example below:
```
                     alfosc.resetxy
                     alfosc.readspeed 200
                     alfosc.xsize 1050
                     alfosc.xbeg 300
                     alfosc.ysize 1350
                     alfosc.ybeg 1
                     alfosc.bin 2    
	     
```
Store current setting and set the necessary FITS header keywords:
system.runstore alfosc
alfosc.propid 74-xxx
alfosc.piname 'PI name'
alfosc.proptitl 'The proposal title'
when you are ready to start the N exposures of exptime t, use the commands:
mexp t N; astrowakeup
You may set N to a large number and Ctrl-C when time is out.
When all is finished do system.runrestore alfosc

The biases with the same detector setup as the observations are taken in the morning by running the scripts alfosc.alfosc-calibs ALxxxx where xxxx is the filename prefix for the date.

Last modified: October 24 2026