The filter wheel is inserted between the focuser and the camera or eyepiece. It allows a quick change of filter by simply turning the wheel.The EFWmini motorized filter wheel is very thin - the filters are only 10mm away from the sensor, so even with high-intensity telescopes there is no vignetting. If you work with unmounted 31mm filters instead of 1.25 filters, you can even use objectives up to f/2, without any annoying vignetting! Power consumption is very low. You can, for example, easily operate the filter wheel through the camera's USB hub (if available).