So in answer the question at the top of the post - Is it possible to have professional m4/3? For me, the answer is yes, with reservations. But thats a situation that applies to many other cameras. No-one would deny that Hassleblad, Leaf, Phase Ones and Leica medium-format are professional cameras, but I doubt they are the system of choice for most wedding photographers, even assuming they could afford them. This is where the DSLR still rules. Fast, reliable and dependable, good in low light and with a large file size, they do the job very nicely. And while a GH3 + battery grip may look the part, I'm not sure that its going to be the whole answer for photographers with a broad and varied client base as yet.
However, for photographers who work predominantly outdoors, or even those who work in a controlled studio environment, high-end m4/3 could indeed work very well as a professional system. With time for careful processing, and shooting at low ISO settings the 16MP file size is capable of significant upsizing and there is no doubt that there are some seriously good lenses now available for the system. Travel photographers have seen the benefits of this for some time.
There is also the point to be made that in many areas of the marketplace, the USA in particular in seems, there just isn't yet an acceptance that small cameras can 'do the job.' Lots of recent figures show that, if anything DSLR cameras are taking back sales from the smaller systems. Panasonic, for example, are still apparently struggling to make any serious inroads into the US market, though if you could actually buy their cameras there that might help! Is this why we have a GH3? Well maybe, but I think that they have realised, like Olympus that if m4/3 is going to be what they base their future on, then they have to offer a wider range of cameras than they have up to now. There is obviously a preference amongst many photographers for cameras that look more familiar. And indeed cameras that have a 'professional' look to them. The problem here of course is that Panasonic and Olympus then come up against the Nikon and Canon juggernauts. It is indeed going to take something special to get people to switch from Canon and Nikon DSLR's to Panasonic and Olympus equivalents. And no they aren't DSLR's but cameras like the GH3 and the upcoming E-M1 sure look like them. And they are certainly priced like them.
Another problem that m4/3 has in a professional marketplace is where the system is going and what potential does it have? The number of megapixels a sensor can capture isn't the whole story as we all know, but how much longer for example, can m4/3 compete with a 16MP sensor? And is it possible to make it bigger and still keep the quality that exists now? Plus of course there is the question is m4/3 ever going to be able to deliver the goods at high ISO settings. In terms of the smaller systems the Fuji X's and Sony RX1 have raised the bar here. These are cameras that produce extraordinary quality at higher ISO settings, which is significantly better than the best of m4/3. Sony are on the verge of an interchangeable system with a 35mm sized sensor and in terms of image quality, m4/3 is going to be unable to compete with that. And no matter what improvements Panasonic and Olympus can come up with the size of the sensor will always probably be a factor.
In conclusion, I would say that for the most part, the linking of m4/3 and professional is still to a large extent an unknown. There is no doubt that Panasonic and Olympus offer some attractive options in many areas of photography that will appeal to and be useful for many working photographers. Video implementation being an obvious example. Whether the system can make a significant breakthrough remains to be seen and it may well be the case that it remains for the most part, at an enthusiast level. For someone like me, it obviously works, but then I'm far from a typical professional photographer. I rarely work with clients these days and can pretty much do as I please and use what I want. But assuming that I was working on a daily basis as a commercial photographer, turning up for all sorts of jobs and trying to put together a system that would handle anything that was asked of it, would I put my faith in m4/3? I think I would have to answer no.
So is there any point to cameras like the GH3 and E-M1? Well yes I think that there is, and many photographers, including myself, will find them attractive. And to a large extent I see no point in attempting to classify these high end m4/3 cameras as professional.They are what they are, and for certain uses they can offer the best option. I see nothing wrong with offering professional features, or indeed a 'professional look' in fact I think in many cases and for many potential customers that would be an advantage, but there is probably no need to try to convince the professional market that these cameras are just what they need. Plus there is of course the simple fact that no company would make money from their high end cameras if only professionals bought them. If only professionals bought a camera like the Nikon D4 then it would probably cost around £30,000 for Nikon to make a profit from it!!!
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