Constructing a Focus Model

Once an automated focus run has been performed as in Section 6.4, a focus model (described in Section 6.2.2 can be constructed. This is accomplished with the idl program find_focus3.pro, which returns a structure with the best focus positions (for debugging purposes), as well as plotting the linear fits to the screen and printing to the terminal the constants for the focus model.

1. Go to the pipeline directory (or the directory that contains corresponding image/ and prod/ subdirectories with the appropriate image and header files) and create a list of the focus images.

   $ cd /rotse/data/pipeline/

   $ ls -color=never /rotse/data/pipeline/image/date_foc*.fit > focus.list

2. Start idl and run find_focus3.pro.

   $ idl

   IDL> find_focus3,'focus.list',best_focs

   MRDFITS: Binary table...

   ...

3. As it is processing, fits like that in Figure 6.1 are plotted. After each plot, the user is asked to confirm that the program has found a good fit. This helps reduce problems from cloudy data and other systematics.
4. When it completes, a residual plot like that in Figure 6.2 is made. The focus model constants (and configuration file abreviations) are also printed:

   ...

   Offset      ("1")  :        3.4426761

   Elev        ("e")  :    -0.0068352453

   Elev^ 2      ("ee") :    3.2436731e-05

   Temp        ("t")  :     0.0044962081

   Temp-Elev   ("et") :    5.8851819e-05

   Temp-Elev^ 2 ("eet"):   -2.4983650e-07

5. Put these constants into a focus model file as described in Section 3.8.1.

Figure 6.2: Plot of focus residuals as a function of temperature and elevation.