Apprendix CFCCD


A filter list is available via WWW and will also be found in NOAO Newsletter No. 34. A complete CTIO filter list is also available via ftp. See the WWW home page.


The 0.9m, 1.5m and 4m CFCCD systems have two filter wheels each holding seven filters up to 3x3 inches square. These wheels are modular, and we have a single wheel which holds five 4x4 filters. This is useful when an observer brings 4x4 filters for use at these telescopes, or it is desired to use a filter which we have in 4x4 size and not in 3x3.


The Schmidt has a single filter bolt which holds five filters up to 4x4 square.


The gain in electrons/adu is usually accomplished using the gfind command (in the contributed package). Here is a cookbook recipe for determining the gain in electrons/adu, for anyone who wants to do all the steps one by one.

  1. Take a sequence of 2 bias frames. Make sure that the preflash is set to zero.
  2. Take a sequence of 2 dome flats or, better yet, 2 bias frames with a big preflash value (giving a total signal of approximately 1/2 saturation).
  3. Subtract these frames as follows:

    BIAS1-2 = BIAS1 - BIAS2 (use imarith)
    FLASH1-2 = FLASH1 - FLASH2

  4. Use the IRAF imstat task to determine MEAN(FLASH1), MEAN(FLASH2), MEAN(BIAS1), MEAN(BIAS2), RMS(FLASH1-2), and RMS(BIAS1-2). Note that it is very important that the stats box be positioned on a region of the CCD free from traps, bad columns, or any bad pixels.
  5. Calculate the gain,

    e/adu = (MEAN(FLASH1)+MEAN(FLASH2)) - (MEAN(BIAS1)-MEAN(BIAS2)) RMS(FLASH1-2)2 - RMS(BIAS1-2)2

  6. The readout noise in electrons is
    RON(e) = RMS(BIAS1-2) * (e/adu) / 1.41