I started posting this thought in another thread, but I think it deserves it's own, in light of the recent Olympus interview. I have long been of the opinion that both Olympus and Panasonic have failed to capitalize on the 2x crop factor, and how it compares to APS-C for users of super telephoto lenses. I'll break down my logic here: Let me preface this by saying, the only "equivalence" I care about is FOV. I'm not looking to start one of those discussions. Most of the traditional equivalence arguments don't have relevance to super telephoto work anyways. If anything, they get flipped on their head. The new 300mm will be great for the system. Here's where it will get us, and what it compares to directly in APS-C for FOV. I include the TC for all of this, because honestly, at these focal lengths, the TC will be on 90% of the time, if not always. It's the max reach with the TC that I'm concerned with, so I don't include numbers for without. Either way, the focal lengths compare directly for FOV. 300mm + 1.4x TC on m4/3 gets you 420mm(840mm equiv FOV) 400mm + 1.4x TC on APS-C gets you 560mm(840mm equiv FOV) That's great. The weight difference between a 300mm f4 designed for m4/3 and 400mm f4 designed for full frame should be significant. This is even true for the compact diffractive optics designs using fresnel elements. The new Canon 400mm f4 DO IS II USM lens comes in at 4.63lbs, and that's the ultralight end of fast full frame super telephoto lenses. I saw the new Oly 300mm quoted at 1500grams, or about 3.3lbs. That's almost a pound and a half saved versus the lightest lens for APS-C that can offer the same reach. And that's comparing a fresnel based design of unknown optical quality(the first version wasn't well received, despite the weight savings), to a traditional design that will likely at least equal the other PRO lenses optically. There are no traditional 400mm f4's that I know of to make a more direct comparison of weight. All the other 400mm are 2.8 or 5.6, so comparing for weight is less meaningful. But APS-C isn't limited to 400mm. Pros who use long lenses always want more reach, up to the point where either they can no longer bear to pay for, or carry it, whichever comes first. I'd say for most of these folks, 500mm is probably as far as they will ever go with a prime. Yeah 600s exist, but they are bloody ginormous, and weigh 5 tons. Here's what a 400mm would get us, and what it compares to in APS-C for FOV. 400mm + 1.4x TC on m4/3 gets you 560mm(1120mm equiv FOV) 500mm + 1.4x TC on APS-C gets you 700mm(1050mm equiv FOV) 600mm + 1.4x TC on APS-C gets you 840mm(1260mm equiv FOV) So looking at equivalent field of view, 400mm plus a 1.4x TC would put us smack dab in between the longest focal lengths commonly used by pro sports and wildlife photographers. This means we could have a lens offering the same reach as the longest lenses used by APS-C pros, with a weight that would likely be similar to the Canon 400 f4 discussed above. Olympus should exploit this possible advantage. They have their focus on imaging, and with the E-M1 soon capable of 9fps with C-AF, and it's generous buffer, they could really make the most of a 400mm prime. I believe that such a lens would draw in wildlife and sports shooters in large numbers, after years of being nudged towards a larger sensor, and being forced to use lenses made for that larger sensor. All those Nikon users waiting for a D400 could buy E-M1mark2's instead. Ok tear apart my logic, or tell me why your focal length is a better idea. Or agree, since obviously I'm correct.