Some useful links:
Descriptions of our CCD Systems:
Loral 2K CCD
A Loral 2Kx2K CCD is the "default" optical imaging device at the Perkins.
The device has 15µm pixels. The field-of-view is 3.2x3.2 arcminutes.
The unbinned pixel scale is 0.0956"/pixel; the chip is commonly binned
2x2 for a scale of 0.191"/pixel. Other binning (3x3 and 4x4) are possible,
and result in scales of 0.287"/pixel or 0.382"/pixel. The chip is linear up
to 80,500e (26,000 ADU at the default gain of 3.1), and appears to be the
same either binned or unbinned.
The readnoise depends upon the time constant;
at the default setting it is 17 e- and the readout time for a 2x2 binned
is 6 seconds. The CCD has good blue
quantum efficiency (35% at 3000Å,
48% at 3500Å, 79% at 4000Å); a QE curve can be found
here.
The "old" Loral died in early April 2001, and the chip described above
was put into service on 17 April 2001.
SITe 2K CCD.
A guide to using the 42-inch and SITe can be
found here.
This is a back-illuminated SITe
2Kx2K CCD with
24µm pixels. The CCD can be used either at the Perkins or at the Hall
telescope, although by default it is used at the Hall. At the Perkins its
one advantage over the Loral is its larger field of view: 5.2 by 5.2 arcminutes.
The system is capable of unbinned operation (0.153"/pixel) and
also 2x2 and 4x4
binned operation (0.306"/pixel and 0.612"/pixel).
This chip also has good blue sensitivity, and a QE curve can be found
here.
Currently it is not possible to read out a subframe with this system so
the read plus
storage time in unbinned mode is long - about 4 minutes. This camera is
normally used
either unbinned or binned 2x2 on the Hall telescope, and binned 4x4 on
the Perkins
telescope without any reimaging optics. A variety of filters are
available including BVRI
glass filters. A liquid copper sulfate U filter is also available but
because of the potential
for freezing, it should be removed from the telescope if temperatures
could drop below 23
F. The SITe CCD is cosmetically good, with two bright columns. At
present it suffers from
some pattern noise, quite low full well capacity, (about 70,000
electrons), and read noise
of about 14 electrons. The gain is about 3.6 electrons/ADU. The hold
time on the dewar in
winter has been seen to be as long as 22 hours.
Some pictures of the SITe on the 42inch are shown here.
NCCD and USNO CCD.
These CCD cameras are based on TI 800x800 WFPC 1 CCDs with the Harris
electronics that
were made available to the community some years ago. They are thinned
and backside
illuminated and have 15µm pixels.
We have been offering the USNO CCD at the Perkins at times that the Loral
is down for some reason; it is used with a 4:1 reduction box.
The unbinned system
has scale of
0.43"/pixel and a field of view of 5.7'. These reducing optics are glass
and have a cutoff
wavelength in the vicinity of 4000 A. The USNO CCD is reputed to have
better UV quantum
efficiency than the NCCD device. A variety of filters are available
including BVRI glass
filters. The USNO CCD is cosmetically very clean and has an extremely
flat bias. The NCCD
has a fingerprint on it that is annoying but flattens out well. The
major drawbacks of the
USNO CCD are that the dewar hold time is in the vicinity of 13 hours.
The binning can be changed to 2x2
by flipping a
switch in the dewar electronics.
Last updated 4 Feb 2002 massey@lowell.edu
