S.B.I.G. MODEL ST-6 SERIES CCD CAMERA SYSTEMS: "CCD imaging technology has arrived"

This model has been discontinued. It remains posted here for information purposes only.

FEATURES OF S.B.I.G. MODEL ST-6B/I/V CCD SYSTEMS:

Keeping with their tradition of innovation, in 1992 SBIG introduced their second generation CCD imaging camera; the original ST-6 Professional CCD Imaging Camera (an earlier version of the current ST-6B). The ST-6 introduced a unique concept (Patented) for astronomical imaging "Track and Accumulate". The ST-6 provided incredible, here to fore unrealized imaging capabilities at an price attainable by institutions, and the demanding amateur. A magazine review of the camera suggested that affordable imaging had finally arrived.

The Model ST-6B is a multi-purpose instrument which features a Texas Instruments TC-241 detector CCD with excellent quantum efficiency and spectral response. An optional Model ST-6V camera is available with a Quartz window that extends the spectral response from the standard 400nm down to 200nm. The TC-241 CCD is mounted onto a pedestal on top of a thermoelectric cooler within the camera head housing. The head also houses an Analog to Digital converter, cooling electronics and fan, and other readout electronics. With its 16 bit A/D converter, and double correlated sampling the images provided by the ST-6 cameras are of photographic quality revealing very good detail and dynamic range (shades of grey, or colors when used with an optional filter wheel).

The difference between the prior Model ST-6A camera and the ST-6B is that SBIG has improved the thermoelectric cooling in the Model ST-6A CCD Imaging Camera by an additional 8 deg. C. Since the dark current is reduced approximately one half with each 8 degrees C reduction this represents a significant improvement in dark current. This will be of particular interest to customers imaging low surface brightness galaxies or imaging against a dark background such as in Raman Spectroscopy. The new Model ST-6B can be operated 55 deg. C below ambient. There are no other changes in the configuration or operating characteristics of this outstanding product. This feature is included with all Model ST-6 CCD Imaging Cameras shipped after October 1997 specified as Model ST-6B.

The ST-6 series cameras will reveal spiral structure in hundreds of galaxies with 1 to 5 minute exposures at the prime focus of an 8" f10 telescope. With such a telescope, stellar photometry down to 18th magnitude is attainable. Planetary Nebulae, Comets, asteroids, become easy targets. Many of these images can be obtained from the comfort of a suburban back yard.

This system permits:

1. When used with a personal computer (Macintosh or PC) the ST-6B and its variants can function as an integrating, cooled CCD camera to capture monochromatic images of very faint objects. It was carefully designed for astronomical and scientific imaging.
   
   
   (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-6B CCD system with a telescope or a camera lens, then employ the following formula:
   
   Horizontal: 57.3/Focal Length of Objective (mm) * 8.6
   
   
   Vertical: 57.3/Focal Length of Objective (mm) * 6.5
   
   

2. When used with the optional SBIG CFW-8 Color Filter Wheel then the ST-6B camera can function to produce tricolor images; these can then be combined (indexed and balanced) to produce color images.

3. When the camera (controlled by a personal computer) is installed on a photoguide telescope, or at the guide port of an off axis guiding device can detect any deviations in tracking of a telescope (in both axes), and then send correction signals via a relay cable to a telescope drive corrector controller; all of this is done with a better frequency, higher accuracy and over a longer period of time than most humans can perform. All of this resulting in professional quality astrophotographs limited only by the quality of the telescope, and atmosphere.

The ST-6 series cameras incorporate a two stage thermoelectric cooler. The operating temperature range is user selectable (via the controlling computer keyboard) and it can be regulated to 0.5 degree precision. A regulating thermistor stabilizes the temperature thereby allowing exposure times of up to one hour with very low dark current.

Connectors on the head are a male 25 pin "D" to a port on the external CPU; this connector is accessed from the side of the camera head to eliminate any risk of binding the cable against the base of fork mounted systems when imaging near Zenith. The external CPU ( approximately 8-3/4" x 5-3/4" x 2") can be placed up to 15 feet from the head. The CPU has a 9 pin male "D" connector for Power, a 15 pin male "D" connector for Relay outputs to control an mounting platform (for uses such as during tracking of celestial objects), a 9 pin female "D" Serial port connector, and a female "D" connector to the Camera head. There is also one 9 pin female "D" connector "AUX" to control an optional Color Filter Wheel. Included cables are: 10 foot long 25 pin "D" female to male for the CCD head to CPU, a cable with a 15 pin female to 14 exposed leads for wiring a Relay control cable (directions are furnished by Company Seven if the drive corrector model is specified), and a PC serial cable if furnished or, a Macintosh cable if so specified. The A.C. power supply is also furnished; this plugs into 115V. Operation is also possible with an optional 12 V.D.C. converter which would usually be desireable to operate a personal computer anyway.

THE ST-6B FUNCTIONS:

THE ST-6B BASIC STAR TRACKER FUNCTION:
The camera head CCD detector consists of array elements, called pixels. The smaller array of pixels, arranged in horizontal ("X" axis) and vertical ("Y" axis) rows, convert photons (the light falling on the detector from a star) in to electrons. When a guide star's image is present at a specific pixel the micro controller will note the increased signal intensity from that pixel relative to the others. An indication of the intensity of the signal and the location (X and Y coordinates) of the star on the detector are read on the control software display of a personal computer.

FOCUS:We suggest a parfocal eyepiece (such as "IFocus" by Software Bisque) be employed to visually find (or use digital or mechanical setting circles), center and focus (or nearly focus) the CCD onto the area to be imaged. Then the eyepiece is removed and replaced by the CCD head. Now select to enter the "Focus" mode. Set the exposure to 5 seconds. Select the 1 out of 4 SUBFRAME mode and center the object using the telescope's hand contol or from the computer keyboard. As the telescope focuser is adjusted to improve focus, more light from the star will be focused onto a smaller area of the CCD, eventually possibly on to only one pixel thereby increasing the intensity which is indicated on the display as a higher value; this is an aid to obtaining precise focus of the star.

In this mode, the camera will continue to take short exposures of from 30 seconds for a full frame - which is not necessary to as fast as every 3 seconds for a 1/16th frame setting. The display screen will automatically refresh and the values adjust accordingly. Once the system is focused onto the star field, the user can slect to view the entire field of view of the CCD and then select any particular star to be that which the CCD will use as a reference for guiding.

The Model ST-6B camera interface to the telescope consists of a cable from the normally closed/open connector of the camera CPU 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 or more (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.

THE ST-6B "TRACK AND ACCUMULATE" FUNCTION:
In operation, the CCD camera can be used as an auto guider full time as it will detect a star, and generate the signals which then drive the relays thereby adjusting the telescope tracking. The camera also has a "Track and Accumulate" (TRACCUM) feature pioneered (and then Patented) by S.B.I.G. TRACCUM allows guiding of long integrated images from as short as 10 seconds to 1 hour. The ST-6 will take an exposure, then determine the position of a preselected star, add the image to the image sum building an internal memory buffer, correct the telescope's position and then star the cycle all over again. In this mode, up to 64 images can be co-addded. The resulting exposure is almost as good as one long exposu re, depending on the exposure time selected andthe actual sky conditions. In another mode, the image is shifted to correct the errors, and added to the image buffer; in this mode the telescope need not be adjusted. With the very good sensitivity of this camera across the spectrum, this virtually assures a selectable guide star will be found within the field of view.

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.

THE TRACK MODE: After calibration, 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.

CAPTURE AND DISPLAY THE IMAGE:

Captture an image of the desired object by entering the GRAB menu, set the exposure time, and then press the Return key. The ST-6 will then expose the CCD for the correc exposure time, and transfer the captured image to the buffer memory.. With the remendous dynamic range of 16 bit A/D converter there is no need to preset the gain or offset levels to optimize the image.

The image can be immediately displayed on the computer monitor using EGA or VGA graphics. Auto contrast can be selected, with computers background and range values, or the background and range values may be manually entered to bring out specific features of interest.

OPTIMIZE AND ANALYZE THE IMAGE:

An image can be substantially improved by subtracting a Dark Frame of equal exposure, which the ST-6 series (and all other SBIG cameras) control software allows. Pixels whihc have a higher dark current value than the average ("hot pixels"), are greatly suppressed and the displayed image appears smoother. The control programs also support the use of flat field calibration frames to corrrect for vignetting and pixel to pixel variations. A number of display options are also available to smooth the image or enhance the contrast. Multiple frames can be co-added to achieve even higher sensitivity.

Entering the CROSSHAIR MODE enables functions such as stellaar and diffuse magnitude measurement, and photometric measurements of stellar positions and angles. The 16 bit accuracy (1 part in 65536) allows very accurate brightness measurements to be made. With apporpriate filters, stellar temperature can be measured!

The potential applications of this technology are still being revealed by innovative operators, sometime with software specifically developed for their tasks!

Specifications of Model ST-6B CCD System Detectors

Imaging Resolution:	375 x 242 Pixels, TI 241 CCD
Imaging Pixel Dimensions:	23 x 27 microns
Imaging Array Dimensions:	8.63mm x 6.53mm, 10.8mm Diagonal
Anti-Blooming:	100x Anti-Blooming

Specifications of Model ST-6B Electronics

Binning:	Variable/Software Selectable
Full Well Unbinned (in Ke-):	400,000
Readout Noise (in e-):	30 RMS Double Correlated Sampling
Dark Current:	1.0e-/pixel/sec @-20 degrees C

Specifications of Model ST-6B Hardware

Desiccant:	Yes, internal
Standard Control Software:	Macintosh, PC Windows or Win95
Communications Port:	Serial
Analog/Digital Converter:	16 Bit
Digitization Rate, Full Frame:	11 sec. w/o Double Correlated Sampling
Digitization Rate, Full Frame:	22 sec. w/Double Correlated Sampling
Shutter:	Electro-Mechanical
Fastest Shutter Speed:	0.1 Sec.
Longest Shutter Speed:	1 Hour
Cooling From Ambient:	-50 Degrees
Power Requirements:	115 V.A.C. Provided (12 v.d.c. optional)

THE ST-6I INDUSTRIAL CCD CAMERA is similar to the ST-6B. It is also available with the Quartz window option for extended sensitivity into the ultraviolet spectrum. The ST-6I camera has a spectroscopy ROM option that permits very wide binning range which include:

Specifications of Model ST-6I Binned Readout Modes

Resolution Mode	Pixel Size (microns)	Typical Dark Current (e-/pixel/sec @-20 Deg. C)
375 x 242 (software Binned)	23 x 27	13
250 x 242 (on chip binning)	34.5 x 27	20
252 x 121 (on chip binning)	34.5 x 54	40
750 x 121 (on chip binning)	11.5 x 54	13
750 x 30 (on chip binning)	11.5 x 216	50
375 x 30 (on chip & software binning)	23 x 216	100
250 x 30 (on chip binning)	34.5 x 216	150
375 x 1 (on chip & software binning)	23 x 6534	3200

Typical Readout Noise (per read @-20 Deg. C)	25 e- rms (Modes 1 to 7)
Typical Readout Noise (per read @-20 Deg. C)	110 e- rms (Mode 8)

POPULAR AVAILABLE OPTIONS FOR THE S.B.I.G. ST-6B/I/V:

• Company Seven can provide wiring diagrams of most common production telescopes to illustrate
  to the user how to wire the provided relay cable into the telescope.
  
• CFW-8 Color Filter Wheel
  
• A variety of nosepieces to fit microscopes or other devices
  
• Image Processing Software
  
• Parfocal Eyepiece to help to find, center, and focus an object
  
• Camera Lens Adapter
  
• Spectroscopy ROM (see the ST-6I information above)