The SBIG FW8S-STXL provides 8 filter slots for 36 mm / 1.25" filters for all SBIG STXL camera models. This filter wheel incorporates a one-of-a-kind micron-precision filter positioning mechanism. When you are taking flat field frames of filtered images, the flat field frame must show the exact same optical characteristics to generate the most effective results. If there is any dust on the filter or uneven illumination caused by the filter, this must be positioned EXACTLY the same every time, or the flat-field will not be able to remove the image artifact. This STXL filter wheel is designed to provide a new level of precision when taking flats through filters by repositioning the filters to within a few microns every time. This allows the system to take extremely accurate flat field frames even after rotating the filter wheel several times, or after a loss of power.
The light frame at top, which is taken with the new filter wheel design, shows a large opaque spot that is caused by debris intentionally stuck on a clear filter. The filter wheel was rotated several times, then the clear filter was repositioned, and a flat field image was taken through this same dirty filter. The image at the bottom left shows the result after applying the flat field image to the original light frame. We measured this positional accuracy to be better than 5.4 microns- which is better than a single pixel!