In HET tradition, the HET acquisition camera is refered to by several names: ACQcam, acam, acm. I prefer acm, because it is the standard 3-character image identifier that is used in naming (nearly) all HET images:

A typical acm image name: 
  20191018T024545.3_acm_sci.fits 

The acm camera sits off to the side of the PFIP and is fed by a fold mirror (the "acquisition mirror") that is inserted when an acm image is to be taken. To understand how we can make a visualization of where the resultant sky image is positioned relative to the rest of the IHMP you can read the documenation on the routine fgstar.

A ds9 view of a DSS image with the IHMP footprint overplotted, including the field of the HET acquisition camera (acm) drawn in yellow. The command used to make this (on mcs as astronomer) was: % fgstar 06:15:20.46 +39:51:50.6 304.0 gc1 N Usage: fgstar 06:15:20.46 +39:51:50.6 304.0 gc1 N arg1 - RA of IHMP center (sexigecimal) arg2 - DEC of IHMP center (sexigecimal) arg3 - Azimuth of HET structure (degrees) arg4 - probe name (valid names = gc1,gc2,wf1,wf2) arg5 - run in verbose/debug mode (Y/N) The acm has an approximately square field of view 3.5 arcminutes on a side. The pixel size is 0.2709 ± 0.0001 arcseonds. In the view above the yellow circle repesents the X,Y=0,0 pixel location in the 775x771 pixel acm image. The thicker yellow line represents the positive Y axis. When the acm mirror is inserted, we see that it covers the same sky locations as three HET detectors: 066, 056, and BIB. The first two are the red and blue IFUs of the LRS2 spectrograph, and the last is the "boresite" imaging bundle (BIB). Lastly, the red circle is the center of the IHMP (Input Head Mounting Plate). This is the plate that holds the VIRUS IFUs (the cyan squares above) and other detectors in the HET focal plane. The locations of these four points (056,066,BIB,IHMP), in acm pixels, are key to pointing the HET. The fgstar routine no longer maintains the present positions for the current acm, but this diagram is a helpful representation for understanding how we position the HET on the sky.

Using the acm does come with some problems, and perhaps the most significant one is that every image reads out with a significant fixed bias pattern (FBP). The figure below shows this FBP derived with 91 bias frames taken on the night of 20210213 UT.

The fixed bias pattern (FBP) of the HET acquisition camera (acm) obstained from 91 bias images taken on the night of 20210213 UT. A mean global bias level has been subtracted from each column-averaged bias value. This median global level is usually around 1375±5 adu, but this value can sometimes change due to things like power-cycling the cRIO (a computer communications device in the PFIP). The edge columns (1 to 50, 750 to 775) show large systematic errors, and these are excluded from computing the global mean bias. The red line is a parabolic fit to the FBP and we see here a low spatial frequency variation acroos the chip from approxiamtely -30 adu at the edges and +12 adu near the center. Fianlly, the large number of "low-bvalued" blue points represent bad zingle columns that can produce systematic signal offsest by up to 100 adu.

On the left is a raw acm image displayed with ds9. On the right is the same image processed by subtracting the mean fixed bias pattern computed for the night or from images gathered over several nights. This processing is computationally inexpensive and it is a true shame that it is not done for every image coming our of the data acquisition code PAS.