I really like the 40mm focal length. I used to like my Canon 5D and Zuiko 40mm and now currenty use a Panasonic G3 and 20mm. I would like to get back to full frame sometime this year and I am looking at the options.
Leica, Canon and Nikon are there but what lens to use. as the Leica framelines seem to not fit with a 40mm lens and are the 40mm lenses for a Canon 5d3 and Nikon 800 just not good enough.
I don't shoot much landscape stuff or fast moving action so manual focus is no problem.
+1 for the Canon 40mm STM pancake, great little lens. Sharp in the center wide open, sharp into the corners at f5.6 or so, nice bokeh at mfd, whats not to like?
I'm another fan of the EF 40/2.8 STM. It's sharper than my Tessar 45/2.8 and Ultron 40/2 (recently sold). I think a 6D + EF 40/2.8 would be a super setup. I haven't got the 6D, yet.
another +1 on the Canon STM.
I've had both SL and SLII Voiglanders (in F mount), and two copies of the (EXCELLENT) Minolta 40/2 they made for the CLE, and I've also had the Nikon 45/2.8P and Pentax 45/2.8.
For SLR use, the Canon is a winner.
For RF use, the Minolta 40 is just wonderful, and extremely small.
I also enjoy the 20mm f/1.7 on my m43 system, as well as 35mm on a 5D. Can't really tell them apart all that much. The 20mm you see of micro fourthirds is 20mm on a 2xcrop system, but keep in mind that it's also a 4 x 3 aspect ratio. If you use 40mm on a 5D, it looks way different due to the 2 x 3 aspect ratio.
Regarding the question itself; ss there such a huge difference between 35mm and 40mm or 40mm and 45mm? I doubt many of these lenses are even EXACTLY their reported focal lengths. In other words, a 35mm prime can easily be 37mm without anyone caring, and a 40mm might be a 39mm.
Most lenses suffer from various degrees of focus breathing, which means they change focal length over the focus distance. I wouldn't really rule out anything based on a very specific focal length.
If you decide maybe to go with APS-C, there are some good 28mm lenses that work great on the Nex-6 - Contax G, Leica Elmarit/Summicrons, Zeiss Biogon. Haven't seen many pics from the 28 ZM, but I've seen lots from the G28 around here that are great, and I'm really liking my Elmarit-M 28 ASPH.
