CD16: FCLS quick notes

Looking at three files from CD16 where we were imaging the FCLS through the flux slit (Slit 7) with the N04679 filter.  These are simple D's and the applied bias was set to 0.5 V (to avoid saturation?).  The three images are below along with the EXES x,y that I found today and the FCLS coordinates.  The EXES x,y that I found was off by 1-3 pixels compared to what was in the lab book, but I don't think that is a big deal.

The FCLS coordinates are, according to Ted Dunham's email in Feb of 2013 and stated in a previous TAAS post, millimeters and the DAOF TAAS FCLS corresponds to a SOFIA platescale of 4.16" per mm.  From the difference between top and bottom image locations, I calculate an EXES platescale of

17.96mm / 376.2 pixels = 0.04774 mm/ pixel

or

0.04774 mm / pixel * 4.16 " / mm = 0.199" / pixel

Our design number comes assuming we are F/10 and have 25 micron pixels and is:

2.06e5 arcsec * 25 microns/pixel / 2.5e6 microns / 10 = 0.206" arcsec/pixel

Looks like we are <4% off from the design number.  Good enough.

For rotation, I first considered the angle between our slit long axis and our columns.  This comes out to be 10.6 degrees (determined by using IDL ROT(image,angle) function and seeing what angle gives best alignment of top and bottom of the slit).  Our slit is rotated -10.6 degrees clockwise from our columns

Comparing our slit to the FCLS x,z coordinates, I first plotted the FCLS coordinates for the spot and noted that the top of the slit ends up in the lower left corner of the plot.  This means our slit is rotated 

180 + atan(fcls_x / fcls_z) = 231.3 degrees

clockwise from the FCLS Z axis.  Assuming the FCLS axes correspond to +elevation (+x) and +cross elevation (+z), this means we are rotated 231.3 degrees clockwise from the cross elevation axis.