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The default binning on LOIS startup is 1x1. To change the binning, click on the "CCD Config" menu in the "PRISM Camera Control" GUI and select the desired binning option. Note that there are also 3x3 and 4x4 binning options, but these have not been tested yet.

4.

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Focusing

1. Take a full-field test frame
1. Identify a suitable focus star and get its coordinates from the DS9 display.
1. Type "source kajfocus.tcl" (if you have not already typed "source prismstart.tcl" at startup).
1. Then do "kajfocus xc yc expt focstart focstep nsteps", where:

• xc - x coordinate of the focus star from step 2
• yc - y coordinate of the star
• expt - exposure time for focus frames
• focstart - starting focus value
• focstep - focus step size
• nsteps - number of focus steps to take

This program will make a subframe around the star, take focus exposures, and run the phot routine. The results are put into a file called focus.dat located in the current image directory. You will see the subframes on the image display as the program proceeds. When complete, the program sets the image format back to the full frame (make sure to take a test image to verify that full framing has been activated). One can determine the best focus by examining the focus.dat file and picking the minimum of a parabolic fit through the FWHM values. Subsequent focus runs are appended to the existing file. The most recent focusing run is at the bottom of the file.

An example of entries in a focus.dat file.:

04:45:28.01 48.86 47.54 3.14 16.48 0.060 2403.25
04:45:49.02 48.32 47.88 3.26 16.44 0.063 2396.46
04:46:10.01 48.75 48.18 2.70 16.49 0.059 2410.10

The values in the file are:

• UT
• image center x (pix in subframe)
• image center y (pix in subframe)
• FWHM (pix)
• rough magnitude estimate
• magnitude error
• background level (DN)

The recommended procedure has moderately large steps of 50 focus units with 9 steps to go +/- about 200 steps from the expected focus value. For example, if you expect the focus to be around 3800 you might start out:

kajfocus xc yc 15 3600 50 9

Using the focus routine in LOIS

1. Make sure that you have sourced the "prismstart.tcl" script
2. Make sure that your object coordinates are correct
3. if your "User Button" window is not open, open it with the "Show User Buttons"
4. Use the !focustool button, this button calls a script that will create the files that the IDL focustool
   procedure uses.
5. Based on the inside or outside temperature, use the appropriate formula
   • F(T_in)=4164.89-7.96(T_in)
   • F(T_out)=4172.22-8.19(T_out)
6. Set the parameters in the focustool button with the parameters set to the follow suggested values:
   • xctr = Star's x position or column value
   • yctr = Star's y position or row value
   • expt = The exposure time that you want to use in seconds
   • focstart = Value found in step e. minus 200
   • focstep = 25 motor steps
   • nfoc = 16 number of times to move 25 steps Note When the seeing is really bad(>3") you should consider 32 time around your best focus position.

Special Notice

If LOIS crashes during the script run. You must redo your storage path configuration in LOIS. See LoisStoreError for information

2. Run the IDL focustool widget to determine the best focus on Saturn

1. In your data directory, there is a focus sub-directory. Change your current working directory to that
   directory with a "cd focus"
2. Run the command idl
3. Compile the focustool program in your IDL window

IDL> .r focustool

1. Run the command "focustool"

IDL> focustool

1. hit the button "Load Data"
2. Select the "focus.list.x" for the most recent focus run. If
   it was your first run the file name will be "focus.list.1".
   This file will be in the focus sub directory in your current data storage directory
3. When the program complete there will be a best focus value display in the data window above the graph.

• Focus Tool Widget:

Image Added

 Then examine the focus.dat file in your data directory and determine the optimal focus. You can iterate the process with a finer focus step

5.Focus vs. Filter

PRISM filters are not parfocal, so you will need to adjust the focus during the course of the night. This process will be automated in the future, but for now you will need to change focus manually. We recommend focusing in the R filter. The offsets from each filter from the R filter are given in the table below. For each filter, the relative focus change from the R filter is given and an example is given (from the night of 25 September 2005, 8pm MST).

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