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SBIG FW8G-STT is a self-guiding 8-position 36mm filter wheel for the STT Series cameras.
This wheel has a guiding CCD and associated optics built into the front cover of the filter wheel, so that the guider picks off light from the guide stars before passing through the filters.
Another unique feature of the STT filter wheel is a positive centering mechanism that precisely re-positions and firmly holds filters in exactly the same position over the CCD every time, regardless of a loss of power or intervening movement of the filter wheel. In our tests, using an STT-8300, the re-positioning of the filters was accurate to better than 5.4 microns after several complete rotations of the filter carousel. This degree of precision means that flat fields taken after the filter has moved and returned are accurate to a single pixel.
The self-guiding filter wheel fits only on the SBIG STT Series of cameras. The wheel has an optical length of 37.3 mm. Together with an STT camera, this results in an optical backfocus of 53.5mm.