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The chart above shows the QE results for sample KAF-1600E and KAF-1600 non-ABG series detectors tested under identical operating conditions. The two samples clearly demonstrate the new version of the detector is much more sensitive than the standard KAF-1600 detector from the UV (ultraviolet) to the IR (infrared). The enhanced detector has good UV sensitivity even out past 350 nm! Assuming that the standard ABG detectors are roughly between 30 to 50 percent less sensitive than the non-ABG detectors, then the enhanced non-ABG detectors are as much as four times as sensitive as the standard ABG detector across the visible spectrum, and ten times as sensitive at the far end of the blue spectrum. We have compared standard ABG cameras to the new enhanced non-ABG camera at the telescope and the enhanced non-ABG camera yields approximately 4 times the signal as a standard ABG detector under similar conditions. The difference is quite dramatic.
As of February 1999 the ST-7E and ST-8E were available without ABG (Antiblooming Gate) enabled. In June 1999 we announced the availability of ABG detectors available for delivery commencing in October 1999. As with prior chips, the ABG versions will suffer some loss of sensitivity due to the ABG structure.
Keeping with their tradition of treating their customers with respect, SBIG and Company Seven are instituting generous upgrade programs: from the prior ST-7 to the new ST-7E, and from the ST-7 to ST-8 or ST-8E. Please read our price listing, or contact Company Seven for the current price and availability.
The dual CCD chip arrangement of the ST-7 and ST-8 series multipurpose cameras permits:
The ST-8E camera head incorporates a Texas Instruments TC-211 and the Kodak KAF-1600E enhanced detector which permit simultaneous guiding and imaging thereby eliminating the need for optional guide telescopes, or off axis guiding hardware to accomplish CCD imaging. Also this technique eliminates any possibility of guiding errors caused by differential flexure of guide telescopes, or mirror shift.
Illustration 1. Relative Size of Common Astronomical Imaging CCD's
To predict actual field of view in degrees (horizontal or vertical) when using the ST-8E CCD system
with a telescope or a camera lens, then employ the following formula:
The ST-8E camera head features a female "T-thread" which accepts a variety of adapters to attach the head onto a telescope, microscope, or other system. Furnished with each ST-8E head are a male nose piece of 1.25" diameter (threaded to accept filters), and another of 2" (threaded for 48mm filters). A quiet, no vibration fan vents at the rear of the head to assist with the cooling functions. Connectors on the head are a female 5-pin DIN for power, a male 25 pin "D" to a computer parallel port, and a female 9 pin "D" connector to the telescope drive corrector/hand corrector for autoguiding or to an optional Color Filter Wheel. Included cables are the 25 pin "D" female to male, a male to male RJ cable with an adapter for the female RJ to male 9 pin "D" adapter. A power supply is furnished (standard 115V or optional 12 V.D.C.).
To predict actual field of view in degrees (horizontal or vertical) when using the ST-8E CCD system with a telescope, or a camera lens, then employ the following formula:
Each head contains two CCD's in parallel; a Kodak KAF1600E for imaging, and a Texas Instruments TC211 for tracking. The two CCD's are mounted onto a common pedestal on top of the thermoelectric cooler within the CCD head housing. These CCD's share an Analog to Digital converter, and other readout electronics. In operation, the TC211 portion of the CCD camera detects a star slightly outside the field of view of the Kodak imaging CCD chip, and it generates the signals which then drive the relays thereby adjusting the telescope tracking. The geometry of the Model ST-8E camera is illustrated in Figures 2 and 3. The ST-8 concept is similar to the ST-7 but, the CCD imaging detector area is larger than that of the ST-7.
The TC211 is identical to the chip used in the popular SBIG Model ST-4/4X guiding systems, and in practice the ST-8E tracking technique is very similar to the ST-4, except the ST-8E integrated concept has evolved to allow the TC211 to acquire and guide on fainter stars. In practice, up to the evolution of these cameras users have employed two separate CCD systems; one for guiding and another for imaging. And up to the introduction of the ST-7/8 and ST-8/8E, no one else has rendered it successful within one single head thereby allowing quicker and easier setup and operation, less complicated cabling, and simpler computer and power requirements.
Illustration 2. The Chip Arrangement within the Model ST-7 CCD Head (similar to the ST-8E)
The Model ST-8E camera interface to the telescope consists of a cable from the normally closed/open connector to the telescope drive corrector or hand control. The camera will produce drive adjustments usually commanded by the telescope drive corrector push button switches. A manual override on the computer keyboard allows the corrections to be made by the user.
By making fine adjustments to the telescope via the computer keyboard, a guide star can be moved onto the detector, or even onto any particular pixel. However, a guide star does not have to be centered onto the CCD detector for the system to function properly. The user can select the length of the star tracker exposure times from 0.1 to 20 seconds (default is 1 second); so stars ranging over 10 magnitudes in brightness can be tracked without adding optional filters. The area of pixels to be used (guide box) can also be adjusted to accommodate very long focal length guide telescopes, or mediocre atmospheric seeing conditions.
AUTOMATIC DRIVE CALIBRATION: Once an acceptable star is found, and when focus is achieved, the operator will select "Calibrate Drive" function so the CCD system will "learn" the characteristics of the telescope drive. The software sequentially activates relays via the camera head output which send a user selectable 1 to 10 second signal to the telescope drive corrector to move the telescope North-South and back, then East and West and back; the telescope will end up returned to the point at which it started. This function "teaches" the CCD system what commands will cause the telescope to move in what direction, and how fast. This calibration feature is invaluable when using a German equatorial mount, or an off axis guider, where the proper direction can be very difficult to guess.
Then the operator will select "Track"; any drifting motion of a star across the CCD causes it to appear at a different pixel at each following exposure. The computer controlling the CCD will then calculate how far the star has drifted and generates a control signal, transmitted through the relays to correct the position. The control signal, and its duration are a function of the star's position error. The camera system can take an exposure (integration), read out all the pixel values, and then calculate and transmit the necessary telescope correction in less than one second.
In the "Track" mode the camera acquires a fresh star image, centers the image on a pixel, and holds that star in position by constantly monitoring it - sending correction signals to the telescope drive immediately after the exposure. The CCD is thermoelectrically cooled to enhance its sensitivity to dim stars. This extreme sensitivity enables guide stars as faint as 8th magnitude to be tracked utilizing as small as a 60mm guide telescope. The rapid calculating power of the computer enables the guide star location to be determined within a fraction of a pixel, enabling better than 1 arc second tracking accuracy. An alarm signal is actuated if a guide star is lost.
Specifications of ModelST-8E Dual CCD System Detectors
| Imaging Resolution: | 1534 x 1020 Pixels, Class II Kodak KAF1600 CCD |
| Imaging Pixel Dimensions: | 9 micron square |
| Imaging Array Dimensions: | 13.8mm x 9.2mm, 16.3mm Diagonal |
| Guiding Resolution: | 192 x 164 Pixels, Texas Instruments TC211 CCD |
| Guiding Pixel Dimensions: | 13.75 microns x 16 microns |
| Guiding Array Dimensions: | 2.64mm square, 3.73mm Diagonal |
| Anti-Blooming | Available |
Specifications of Model ST-8E (non-ABG) Electronics
| Binning | 2x2 Noiseless/Software Selectable |
| Full Well Unbinned (in Ke-): | 370,000 |
| Full Well Binned 2x2 (in Ke-): | 160,000 |
| Readout Noise (in e-): | 15 RMS Double Correlated Sampling |
| Dark Current | <0.2e-/pixel/sec @-10 degrees C |
Specifications of Model ST-8E Hardware
| Desiccant: | Yes, internal & replaceable |
| Standard Control Software: | PC Windows or Win95 |
| Communications Port: | Parallel |
| Analog/Digital Converter: | 16 Bit |
| Digitization Rate, Full Frame: | 11.5 secs. at 33 KHz |
| Shutter: | Electro-Mechanical |
| Fastest Shutter Speed: | 0.11 Sec. |
| Longest Shutter Speed: | 1 Hour |
| Cooling From Ambient: | -35 Degrees |
| Power Requirements: | 115V.A.C. Provided (12 v.d.c. optional) |
(Click image to enlarge)
