Each FW also contains an open position. FW2 also contains a blank for taking darks and cold pupil stops to block the left or right telescope aperture for single sided imaging (i.e., this can only be done using the filters in FW1), and blocking filters to compensate for wavelength leaks from the filters in FW1. Filters in FW2 can in principle be (but are not commonly) used for science.
Transmission curves of the science filters in FW1, if at hand, are shown below below.