I have a 70-200 F/4 IS and the 1.4x. The lens is excellent but I've only shot it with the 1.4x only sparingly becauseI also have a 300 F/4 L IS. I have shot the 300 with the 1.4x a lot and there is only avery small loss of sharpness when wide open. The 70-200 F/4 IS is one of the sharpest zooms that Canon makes so it should be fine with the 1.4x.


I also have a 24-105 F/4L and it's a great lens. It's attached to my 5D MkII most of the time. If you are going to be shooting a lot of landscapes, the 24-105 F/4L may not be wide enough for some applications. I don't own the 100-400 F4L but a friend of mine has one. It's a BIG lens compared to the 70-200 F/4 so it's not so discrete to use. (I was doing some shots off a ferry from Vancouver Islandthe other daywith the70-200 F/4 and it was drawing a lot of attention. One couple though I was a pro. (no)).