LUMICON Multiple Filter Selectors allow you to easily switch filters without having to thread and unthread them from your eyepiece or diagonal. The nosepiece also has a filter thread for one more filter. This "Stacking" of filters, such as a neutral density or polarizing filter in front of your other filters can be very useful. By leaving one slot in the slide open you also get to compare views with and without your LUMICON filters. This device is machined from solid aircraft aluminum. It adds 2.2" of height to your focuser.