Originally posted by Na Horuk I have the 35mm f2.4 as well as the 40mm XS. The 40mm XS is probably more practical for carrying around. I mean, if you go for a walk and you have a zoom lens on there, but want to have a high quality prime with you as well - the 40 XS is a good idea, just put it in your pocket.
The 40 is probably slightly sharper, but the 35mm is wider and faster. Both of these lenses in my experience are not quite great when wide open - they are perfectly sharp, but they have some fringing or chromatic aberration, when wide open in high contrast light, so that isn't a very common scenario anyway.
Oh, and the 35mm you can maybe find in white to fit your camera's color (from Japan, or online).
Regarding the filters for the 40mm XS.. yes, they need to be 27mm, which can be hard to find in a store, but there is quite a selection online (for camcorders, but it should work on DSLR's just as well). Mostly from the following brands: Massa, Hoya, Hama, B+W. They have UV, polarizers, even some color filters. I am currently waiting for a filter to arrive from Hong Kong, so I can't talk about the actual quality yet. Hoods might be harder to find for that size, since the hood tends to be bigger than the actual lens lol
I've thought about the 40XS and its size is fascinating (and potentially a plus) but your points about filters and hood are ones that have kept me from buying a 40XS. When I do a search on Amazon for 27mm filters there are a lot that are NOT 27mm that show up too. When all sorted out the ones that are left are Zeikos, Opteka, No-Name brand, Platinum Plus, Sunpak, Digital Concepts, Bower, Canon, Kenko (1 CPL), Hoya (1 UV), and Pentax (1 set for the K-01). I don't see any of the high end makers and Kenko and Hoya models offered are not their better quality filters. So, for the 40XS you are stuck with inferior filters if you want to use filters with the lens.
EDIT: I found some B&W filters in 27mm at Adorama (CPL, ND, 1A) but again these are not their highest quality - although they are better than anything else offered in 27mm that I can find.