The QSI 540 camera employs a 4.2 megapixel Kodak KAI-04022 interline transfer CCD image sensor with microlens technology. The high quantum efficiency, wide dynamic range and low noise performance make the QSI 540 ideally suited to a broad range of demanding astronomical, scientific, medical and industrial imaging applications. The larger field of view offered by the 21.4mm diagonal CCD in the 540 makes a great combination with a wide variety of telescopes and other optical systems. Electronic Shutter All 540 models utilize the electronic shutter built into the KAI-04022 CCD image sensor to control exposures. Shutter timing is very precise and can range from as short as 100 microseconds up to 240 minutes. Mechanical Shutter The Model 540s camera adds the optional internal mechanical shutter in the 'mid-size' camera body configuration. When operating with an interline transfer CCD, a mechanical shutter is not used to actually make the exposure. This is still the responsibility of the electronic shutter. The mechanical shutter is employed to cover the CCD and simplify the creation of Dark and Bias frames for subsequent image processing. Internal Colour Filter Wheel The Model 540ws adds an internal five position filter wheel to the camera in the 'full-size' camera body. Because the internal colour filter wheel is positioned so close to the focal plane, the 540ws is able to provide excellent results free of vignetting even with optics down below a focal ratio of f/4.5. The filter wheel accepts any standard 1.25 inches filter. Various filter configurations are available. Integrated Guider Port The Model 540wsg camera has the internal mechanical shutter and color filter wheel like the 540ws, plus it adds an Integrated Guider Port. This allows guiding using the light from your main telescope while picking off the light from the guide star in front of the filters.