CFHT, Instruments, Imaging, UH8k

The UH 8k Mosaic at CFHT

User's Manual
Please note the date of revision.
Read this page too! (Updates are included on this page which may not appear in the above manual, or which are contrary to statements made in that manual.)

  • For more detailed information, observers should contact Gerry Luppino at IfA, UH or Dennis Crabtree at CFHT.

  • Observing and other notes
  • Dark Current Map
  • Filter Transmission Curves
  • Updates
  • Scattered Light
  • New Script Tools
  • Technical drawings and documents
  • Continuous Bias & Noise monitor@
  • General Characteristics
  • Stability of Dark Current

  • Observing and other notes:

  • The names of a few old "mcdcom" commands have been changed. Please check the new list (also available by typing help). Note, especially, that old scripts may need to be changed to run with the new command set.
  • A graphical form now provides access to all the basic functionality. Please take a moment to view a demo copy of this form and the help window that it contains.
  • A B filter is now available.
  • The software now makes no assumptions about filter or shutter position if it is restarted.
  • Rotating the prime focus bonette can change the spatial sensitivity of the array and it is recommended that observers do not rotate the bonette if they are using superflats or sharing data with other observers.
  • DO NOT move the guide probe during an array readout. This will inject noise into the CCD images.
  • The images are read out as 8 separate FITS files with both horizontal and vertical overscan pixels. The pixel format is signed 16-bit with a BZERO offset on 32k.
  • Reduced data from the first two runs with the camera in March and September 1995 show the CFHT wide field corrector can deliver superb images over the entire field. In the September run, we achieved images under 0".5 FWHM on two consecutive nights.
  • The sensitivity of the array is similar to that of Loral-3 (except in the blue since Loral-3 is phosphor coated while the 8K CCDs are not).
  • Photometric Zero-point: m1(V) = 24.37 m1(I) = 24.31 where: m = m1 - 2.5*log[ADU/s]
  • Flat fielding: best results are obtained using superflats. If these cannot be obtained, use twilight flats for large-spatial-scale variations, and dome flats for pixel-to-pixel variations.
  • Dark frames: for best results, obtain dark images of the same integration times as the science frames they will be used to reduce. But see.

    Update, 4 Sept 1997

    A new version of the CCD control programme is under test and may be available for use by visiting astronomers sometime soon. The command set for this programme will be:
    mosaic <mode> : Set mosaic dspcode (<mode>=full, bin2, bin4, focus, or find)
    etype <c>     : Set exp type o)bject, b)ias, d)ark, f)lat, c)omp or x for focus
    etime <secs>  : Set exposure time to <secs> seconds
    fits <c> <val>: Sets fits card `<c>' to `<val>' for next write
    go [n]        : Start taking (n) exposure(s) (default=one)
    clear [n]     : Clear (wipe) CCDs (n) times (default=once)
    idle          : Recalibrate and continuously clear CCDs
    readout       : Read out the CCDs (eg. as final step in focus sequence)
    writefits     : Re-write the last FITS file, if still in memory
    filter 0|1    : Move filter 0 or 1 into position
    shutter o|c   : Directly control the CCD shutter (o=open, c=close)
    istat         : Compute simple statistics on image currently in memory
    cd [dirname]  : Change/Show current working directory for images
    ls [files]    : List files in the current working directory
    help          : Displays this help screen for uh8kcom
    builtin       : Displays help for director builtin options
    !...          : Passes ... to a unix shell (e.g. `!ls -l *.fits')

    Technical drawings that are available:

  • the CFHT prime focus mounting plate
  • a "face-on" view of the entire instrument.
  • A filter holder. and AutoCAD source
  • Technical documents that are available (local access only):

  • Setup instructions
  • Startup instructions

  • General properties:

    Arrays: 2048 x 4096 3-edge-buttable CCDs arranged in a 4x2 mosaic with 8192 x 8192 pixels
    Pixel size: 15 microns (0''.21/pix at CFH PF).
    Field of View: 29' x 29'
    Gaps: Approx 0.5 to 1 mm
    Image quality: We have data that shows images of order 0''.5 over the entire field.
    Filters: Presently B, V, R and I available (others can be purchased -- size is 150mm x 150mm. Present filters are ~10mm thick. Filters can be up to ~15mm thick). Approximate to Kron-Cousins, with I filter "kind of wide and on the red side."
    NOTE: there is space for only 2 filters in the filter slide.
    QE: Frontside illuminated CCDs -- approx 45% peak QE in the 600-700 nm range -- little or no sensitivity below approx 450 nm. (NOTE -- the sensitivity of this mosaic is nearly identical to that of Loral-3 except in the blue, where Loral-3 was phosphor coated and had some response, whereas these CCDs do not. In the VRI bands, calculations made using the Loral-3 CCD response will appply to the 8K mosaic).
    Readout noise: 6-15 e- depending on the array.
    Dark current: At the operating temperature of these CCDs, the dark current is not negligible. It ranges from 0.05 to .1 e-/sec depending on the array. However, for broad band imaging with typical exposures of 600s or more, the sky shot noise is still the dominant noise term.
    NOTE: Dark frames must be acquired.
    NOTE: For best results, obtain dark frames of the same integration times as the science images they will be used to reduce.
    Cosmetics: All of the CCDs have some cosmetic defects -- some worse than others. The 4 CCDs in the center are of the best cosmetic quality. The cosmetic defects amount to less than a few percent of the detector area for all but one device, which has a bad patch that renders ~10--15% of that array unuseable.
    Readout time: 6-7 minutes for the whole mosaic.