Test of 1-amp readout of HDI from each amplifier

Michael Richmond
Jan 16, 2017

The HDI command shell includes several commands for setting the readout mode of the chip. By default, when one turns on the camera, it is in 4-amp mode. One can issue the following commands to choose 1-amp readout modes:

  command        comment in "help" screen
------------------------------------------------------------------------
  oneamp ur      Temporary mode for "Upper Right" amplifier only
  oneamp ul      "Upper Left" amplifier mode (image display incorrect)
  oneamp lr      "Lower Right" amplifier mode (image display incorrect)
  oneamp ll      "Lower Left" amplifier mode (image display incorrect)
------------------------------------------------------------------------

Most HDI users choose the 1-amp mode oneamp ur.

On Jan 16, 2017, I decided to try reading out the chip using the other amplifiers, just to see what would happen. These tests are rather informal:

• made during the day on a cloudy afternoon
• telescope in zenith park position
• telescope cover ON
• dome lights off, flatfield lamps off -- only ambient light
• Harris R-band filter in place

I found that an exposure time of 60 seconds would admit sufficient ambient light to produce several thousand counts above the bias level; the light level did change with time, likely due to clouds moving across the sky. However, for the very rough purposes of this test, a general diffuse amount of light is sufficient.

The column labelled "stripe" is discussed below.

   image              amp    exptime    counts (incl. bias)   stripe?
---------------------------------------------------------------------
c7769t0005o00.fits     ur     60         3400 - 4900            no
c7769t0006o00.fits     ul     60         4500 - 4600            no

c7760t0007o00.fits     lr     60         2860 - 2870            no
c7760t0008o00.fits     ll     60         2740 - 2750            no

c7769t0009o00.fits     ur     60         4100 - 5100            no
c7769t0010o00.fits     ul     60         4500 - 4600            no

c7769t0011o00.fits     ur     60         4600 - 4700            no
c7769t0012o00.fits     lr     60         2860 - 2870            no

c7769t0013o00.fits     ll     60         2740 - 2750            no
c7769t0014o00.fits     ur     60         4300 - 5200            no

c7769t0015o00.fits     ur    600        20000 - 21000          yes 
c7769t0016o00.fits     ul    600        35000 - 36000          yes
---------------------------------------------------------------------

I draw two conclusions from these images:

• only the ur and ul amplifiers provide real measurements of light striking the chip in 1-amplifier mode. The lr and ll amplifiers appear to produce counts consistent with bias only.
• the "horizontal stripe" defect (see picture below) appears in high-signal images produced by both the ur and ul amplifiers. It does not appear visible to the eye in low-signal images.

The "horizontal stripe" is a feature familiar to users of the camera. In flatfield images with high counts, the eye easily discerns a pair of horizontal lines running across the middle of the image, in rows 2056 (lower pixel counts) and 2057 (higher pixel counts).