New high-res CCD cameras for far-out images
By Alan Brandon
December 1, 2009
The Santa Barbara Instrument Group (SBIG) is adding two new models to its line of specialized, high-resolution CCD cameras for astrophotography and spectography. The ST-8300M and ST-8300C both feature an 8.3 megapixel CCD, thermoelectric cooling, and a USB 2.0 interface. The camera bodies accept both standard c-mount and Nikon lenses making them suitable for a variety of applications. SBIG claims the cameras’ antiblooming and microlens technology improves their sensitivity. Both cameras can also be used as autoguiders to control motorized telescope mounts.
The new ST-8300M (monochrome) and ST-8300C (color) cameras are based on Kodak's KAF-8300, 8.3 megapixel, full frame CCD. This 18 x 14mm (0.7 x 0.6 in.) CCD can be used in high resolution (unbinned) mode with short, fast optics and camera lenses. For longer focal lengths, such as found on Schmidt-Cassegrain telescopes, the CCD can use binning (in which neighboring CCD pixels are grouped together to provide higher sensitivity, but a lower effective resolution).
Binning not only helps optimize the CCD sensitivity, but it also speeds up the download rate for the CCD image. SBIG says its software drivers allow you to select the binning modes and partial frame mode to suit your subject and conditions. For example if you are imaging planets, the camera can be used in high-resolution mode while downloading only a quarter-frame to speed up the data collection process. On nights with less visibility, the sensor can be binned in full frame mode to match the conditions but still maintain the full field of view.
The ST-8300C and ST-8300M both feature a USB 2.0 port which SBIG says can download a high resolution, full frame image in about 7.5 seconds. The cameras also include an I2C accessory serial port for connecting filter wheels, and an autoguider port for controlling the telescope mount.
When the camera is used as an autoguider, it takes multiple short exposures of a particular area of sky and compares the images to determine the apparent motion of one or more stars within the image. The autoguider then issues the appropriate corrections to the motorized telescope mount to keep the telescope pointed in the right direction. This capability not only keeps your desired object in view, but also helps eliminate streaking of the image during long exposures due to the earth’s rotation.
The SBIG cameras each feature a mechanical shutter for taking dark frames, which help to minimize image noise in long-exposure images. A dark frame is an image captured with the sensor in complete darkness, like leaving the lens cap on. The image processor compares several dark frames and subtracts the average noise from subsequent images to reduce that noise.
The ST-8300C/M cameras include an AC power supply, but will run on 12 Vdc for field work. The cameras also feature an integrated fan for thermoelectric cooling. Cooling is essential for maintaining the sensitivity and linear response of the CCD sensor.
The SBIG ST-8300C and ST-8300M include various cables, software, and drivers, and will be available in December from Santa Barbara Instrument Group and optical resellers. The list price is US$1995.