Subject: unsettling observations with DSC

From: Stupendous Man

Submitted: Sat, 13 Apr 1996 03:08:25 -0400 (EDT)

Message number: 31 (previous: 30, next: 32 up: Index)

  Heidi Newberg and I have used the DSC on the 3.5-m several
nights recently, and we have come to several conclusions:

     1. If the baffle is not in place when the DSC is used,
        scattered light (from beyond the tertiary, probably)
        enters the camera.  So, use the baffle (and move
        it as close to the primary as possible).

     2. There appears to be a light leak in the filter slide,
        even if it is covered with tape.  We asked Eddie to
        shine a flashlight at the filter while taking a dark
        exposure, and got a lot of light in a roughly circular
        blobby pattern at the center of the image.

     3. There appears to be a _different_ light leak in the
        shutter.  We asked Eddie to shine a flashlight in the
        aperture of the camera when it was dismounted from the
        telescope, and got quite a different pattern of 
        light on the chip.

     4. The new overscan rows help to remove the bias signature
        from each individual image.  Rah.

  Preliminary analysis of some repeated imaging of the same fields
seems to show that 40 minutes of exposure in Harris R-band with
1.7 arcsec seeing yields a S/N around 10 for R=23.  

  Oh, and, most important, clouds cover the mountain when Heidi's
time begins, and leave JUST when her time is up.  This is the 
3rd time in a row that it has happened ....

                          Michael


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