Newsletter - 2 July 1993
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CCD News - June 1993
The new controllers (GenerationIII) are now in service for both CCD and
Redeye (NICMOS3) camera control. The system is quite stable and delivering
good performance, though we will continue to work on reducing readout
time, which is currently about 5 minutes for the 2048x2048 format CCDs
including all system overhead. Available with the new controller
is a new 2048x2048 CCD, Loral3, which is a blue coated, thick front illuminated
device. Performance and cosmetics are excellent with this CCD and it
replaces essentially all other thick devices (Lick2, SAIC1 and PHX1) in
virtually all applications. For cases where smaller than 2048x2048 formats
are required (HRCam for example) a subarray that includes overscan can be
selected. The exceptions to this are where high QE is more important than
field of view and readout noise and so the RCA2 and 4 devices may be a better
choice, and in cases where CCD scheduling conflicts arise (here Lick2 will be
included in the solution).
Thanks to the careful data reduction done by Greg Fahlman, an exposure timing
error in the Lick2 CCD camera system (tied our older CC200 controllers and
electronics) has been found. We found that all exposures were short by 0.242
seconds. For instance, a request for a 10 second exposure yields only 9.758
seconds of shutter open time. As this is a constant error (ie timing is quite
linear), it will impact short exposures most strongly (such as photometry of
bright stars in exposures under 20 seconds). Data taken from July 92 to the
present should be corrected for this problem. If you have any questions about
this problem and data collected with Lick2 feel free to contact me about it.
A correction to this problem has now been made to the system software (made
6/93).
Observers using the new GenerationIII controller should be aware that an
overscan in the X direction (along rows) of width 40 pixels is automatically
added to all images regardless of raster sizes. We found that taking this
approach, as opposed to a user-adjusted parameter, greatly simplified the CCD
control software and guaranteed that adequate overscan would be attached to all
images. The system overhead to do this is negligible in typical focus mode and
observing mode raster sizes.
In our previous CCD controller, CC200 system, we filled in several exposure-
related FITS cards with externally generated data (ie exposure time from a UNIX
timer and CCD temperature from a CAMAC ADC module). With the GenerationIII
controller (offered with the Loral3 2048x2048 CCD) we measure those values
directly at the CCD with a utility card that is part of the CCD controller
system. Thus the values now put in the FITS cards should be more accurate and
reliable (the exposure timer, for instance, is accurate to about 1 ms).
CURRENTLY AVAILABLE CCDS
The devices listed below represent the CCDs now on line at CFHT and will be,
baring catastrophe, available during semester II of 1993.
CCD C A PS RR GN RN QE350 QE400 QE600 QE800 QE900 T FW Lin
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PHX1 1 512x512 20 92 2.6 8 .15 .15 .42 .30 .15 t,bc 32k 32k
RCA2 1 640x1024 15 68 8.8 50 .15 .55 .82 .40 .18 b,nc 32k 7k
RCA4* 1 640x1024 15 68 4.4 64 .15 .52 .77 .40 .18 b,w 32k 14k
SAIC1 1 1024x1024 18 108 1.6 8 0 0 .40 .30 .15 t,nc 32k 28k
Lick2**1 2048x2048 15 110 2.3 9 0 .05 .45 .40 .20 t,bc 32k 32k
Loral3 2 2048x2048 15 75 1.9 8 .15 .15 .45 .40 .20 t,bc 32k 30k
C = Controller type: 1 = older CC200, 2 = new GenerationIII controller
A = Imaging area of CCD array in pixels.
PS = Pixel Size in microns (all pixels are square).
RR = Read Rate in microseconds/pixel (chip to disk/screen).
GN = Gain or conversion factor in units of electrons per ADCU.
RN = Read Noise in electrons.
QE = Quantum efficiency at a given wavelength (nanometers).
T = Type of CCD; t-thick,front illuminated; b-thin,back illuminated;
bc-blue coating; nc-no coating.
FW = Full well in ADC units.
Lin= Point at which the device is begins to become non-linear in ADC units.
* - Both RCA2 and 4 are thinned, backside illuminated CCDS. However, RCA4 is
physically flatter as it is supported by a thin glass window. This window
causes increasing fringing towards red. RCA4 can not be binned.
** - Lick2 requires special instructions for subarrays - check with CFHT staff
for more information.
WORK IN PROGRESS
The following is a list of CCDs that we hope to release sometime in the
second semester of 1993, though the exact data is impossible to predict
right now. The numbers associated with these device are projected
values (except for A and PS). These should not be taken as absolute and
observing programs should not be developed around them, as only the Tek3
chip is in hand, the others still under development.
CCD C A PS RR RN QE350 QE400 QE600 QE800 QE900 T
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Tek3 2 1024x1024 24 40 6-8 .15 .40 .80 .60 .15 b
Loral4 2 2048x2048 15 40 6-8 .30 .50 .90 .60 .15 b
Ret1 2 2048x2048 13.5 40 5-8 .30 .50 .90 .60 .15 b
The Tek3 CCD is a thinned Tektronix CCD that should offer reasonably high
QE. When operational, lab test will be conducted to study fringing.
Loral4 will be a result (if successfully completed) of a collaboration
between CFHT, IfA and Steward Observatory. This device, a thinned Loral
design, will have an AR coating tuned for the red to minimize fringing in
spectrograph applications. A second device, Loral5, will be thinned and tuned
for blue applications (depending on the outcome of the first chip).
An order has been placed with EG&G Reticon for the acquisition of a thinned
2048x2048 CCD. A project to develop and market thinned 2048x2048 devices
has been underway now for several years at Reticon and may produce
devices by the end of this year.
Christopher Clark
Detector Group
CFHT
email: chris@cfht.hawaii.edu (Internet)
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