I can't remember length off hand, but the v. III 28mm's a long lens with 49mm diameter filter and a large hood. I've seen but never used one, and I was surprised how large it was. On the M7, the smaller 28mm/2 Summicron ASPH intrudes into the 28mm frameline corner, the new 28mm/2.8 Elmarit ASPH hardly does without the hood.
The new 28mm/2.8 is very small, very good and so flare resistant that it hardly ever needs the hood except in strong sidelight situations (sun just out of frame for example)