Does the shorty-forty not take filters?
It does - has a 52mm thread (that also serves as a mount for the dedicated - and basically useless - lens hood). But I don't use a filter on it for two reasons. First, the front element is tiny, and the cost of the lens is low. Second, amd most importantly, the reason I use the 40/2.8 is for portability - it's a thin enough lens that when mounted on the camera, I can slip the setup into a Lowepro Utility Bag 100 AW, and that can go inside my laptop satchel, etc. Likewise, when shooting with another lens, the 40/2.8 easily fits in a pocket. Adding a filter would make it slightly thicker, enough to limit the utility, IMO (the lens protrudes such a short distance from the body than even a 3.4mm XS-Pro filter is a significant proportion of that thickness!).