HSC instrument parameters

Detectors Hamamatsu Photonics KK 2048x4096 (S10892-02)
Number of CCDs 104 for science + 4 for auto guider + 8 for focus monitoring (1)
Pixel size 15 um
Pixel scale 0.17″
Field of view 90 arcmin diameter
Gain 3.0 e/ADU
Read noise 4.5 e-
Readout time 20 sec (2)
Saturation level 150 000 e-
Number of filters maximum of 6
Filter exchange time ∼30 min (3, 4)

  1. See “CCD information” for the detail. The CCDs are arranged on the focal plane with two different gaps of approximately 12 arcsec and 53 arcsec between neighboring CCDs. We recommend that you should use dither steps of 120 arcsec or larger. For covering a contiguous region of sky, 3 exposures are required at least.

  2. The “20 sec” is the time necessary only for reading out signals from CCDs. The overhead time (necessary time from the end of the last exposure to the beginning of the next exposure) is about 30-40 sec, which includes transferring data from HSC to computers, moving the telescope to the next dithering position, and so on.

  3. Before starting a filter exchange, it is necessary to move the telescope to the zenith position and rotate the instrument rotator to the appropriate angle (∼0°). We also need to close the cover of the primary mirror for safety operation.

  4. After changing filters, the telescope is still located at the zenith position. You may need extra overhead time for moving the telescope to your next target. The maximum slew speed of the telescope is 0.5 deg/s for both AZ and EL directions. Please also note that you usually need to do a focus check, which takes about 5 minutes, just after a filter exchange.

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