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Model CFW-8 Color Filter Wheel

SBIG pioneered tricolor imaging by developing hardware and software to register and color balance Red, Green, and Blue images that display spectral emission of deep space objects. When interference filters are carefully selected to match the spectral regions of ionized gases the images taken through the filters can be summed together to represent the distribution of these gases. SBIG designed the following interference filters for use with the CFW-8:



Color Filter Passbands

Filter Passband (nm)
Red 612-670
Green 488-574
Blue 392-508

Tricolor images are taken through the CFW-8 Color Filter Wheel and processed with CCDCOLOR or the new CCDOPS for Windows software. The primary color images are taken through Red, Green and Blue filters. After the images are taken they are processed with the software to co-align the Red, Green and Blue images. The co-aligned image is then color balanced on the computer monitor to become a tricolor RGB image, which can then be saved to disk. The CCDCOLOR or CCDOPS for Windows software also allows the user to perform image processing functions such as smoothing and sharpening as well as saving images in TIFF format.

The CFW-8 system is designed around the standard T-Thread. At the back end the system aliaches to the imaging camera with a male T-Thread adaptor and can also be "direct connected" to the Models ST-7 or ST-8 imaging cameras for a thinner, more rigid mounting. On the front end a variety of T-Thread accessories are available including 1.25 inch (included) and 2 inch diameter nose pieces as well as a "Visual Back Adaptor" for direct connection to SCT's.

The CFW-8 is operated through the CCDOPS software and utilizes a closed loop stepper motor system with positional accuracy of  0.01 inches. It holds up to five standard 1.25" diameter thread-in filters. Also supplied with the unit are Red, Green, and Blue (RGB) interference filter sets and a clear filter (focusing). The new SBIG RGB filters also block Infrared (IR) so an inline IR Blocking filter is no longer required. These filters are mounted in standard size cells that normally fit into 1.25" eyepiece barrels. The CFW-8 adds back focus of approximately 1 inch.

Although some examples of tricolor imaging are shown in this catalog it is difficult to display the wide range of techniques that our customers have developed. The CFW-8 can produce photographic quality tricolor images that rival color astrophotographs.   However, these RGB images also contain an entirely new and added level of valuable information; the identification and distribution of different ionized gasses in an object. SBIG also furnishes precision UBVRI filter sets with the Model CFW-8, filters which allow the user to perform color photometry to measure the classification and temperature of objects.

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Red Image Green Image
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Blue Image Combined Image

Note: The three separate Red Green and Blue CCD images
are not identical. Each one displays only the spectral region
that the filter allows to pass. Since each filter corresponds
to a known spectral region the combined image displays
the distribution of those ionized gases.


1.    Using the CFW-8 and CCDOPS software take three images with relative exposure ratios of (typically) 1:1:1.6 through Red, Green,and Blue filters respectively.
2.    Using CCDOPS COLOR or the new CCDOPS for Windows software register the three images and color balance them on the computer monitor.
3.    The result is a tricolor image.


The Model AO-7 has been specifically designed to enable an ST-7 or ST-8 user to obtain the ultimate in image resolution that his/her telescope and site can achieve. SBIG has exploited the second guiding CCD detector in these imaging cameras to stabilize stellar images, enhancing resolution. The AO-7 system has two components: a high speed tip-tilt mirror for atmospheric correction, and new image enhancement software implementing the Lucy-Richardson algorithm.


Utilizing the second guiding CCD as an imaging sensor the guide star's position is read out at rates up to 40 times a second, and the tip-tilt mirror adjusted to hold the star on the designated pixel for the length of the imaging CCD's exposure. The tip-tilt mirror moves and settles to within 20% of the commanded position in a mere 10 milliseconds, dramatically faster response than any telescope drive is capable of achieving. The result is sharper stars, and more clearly defined nebular features. As a general rule one can guide at 10 frames a second on a 10th magnitude star with a 10 inch (25cm) telescope. The range of the mirror for the Model ST-7 is 5O pixels or 2 arcminutes of correction with an 80 inch focal length telescope, enough to accomodate the periodic error of many mounts without bothering to correct the RA drive axis directly. The Model AO-7 can do all of the guiding. Inexpensive telescope mounts are now entirely capable of producing well guided images.

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As can be seen in this comparison image the AG gives
an improvement in core intensity and halfwidth,
improving the image resolution.


SBIG, in association with Benoit Schillings and Brad Wallis, has developed a Lucy-Richardson image sharpening program that produces dramatic improvements in image detail, visually at least a 2x improvement. The algorithms used are similar to those used on the Hubble Space Telescope images.  The results are the best we have ever seen from amateur telescopes.

The enhancement program is Windows 95 compatible, and resembles SBIG's new Windows processing products, not the well known CCDOPS which runs in the DOS environment. In addition to the enhancement capability, the program allows the display of multiple images, modification of background and range to enhance visibility of detail on the monitor, a crosshairs mode for inspecting pixel values, negative image display mode, and horizontal and vertical image rotation.

The AO system can be retrofitted to all Model ST-7 and ST-8 CCD imaging cameras by inserting a new ROM and loading the upgraded software that accompanies the system. This can be easily done by the user at his site. This remarkable system promises to have a profound effect on CCD imaging by reducing the atmospheric turbulence, wind induced vibrations, and eliminating the remaining periodic errors in most telescope drives.

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Model AO-7 corrected 300 second CCD
image taken with Model ST-7 at the prime
focus of a C-11. The stars in this remarkable
image are 1.0 to 1.1 arcseconds in diameter.

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