[jdietrich]

>A good mirrorless could take most of these shots as well, though I suspect by the time you installed a lens long enough for the wildlife shots[1], it wouldn't be much lighter than the DSLR.

That's one of the big advantages of Micro Four-Thirds - if you're willing to sacrifice a bit of sensor area, you get very bright and lightweight telephoto lenses.

[paulmd]

Why stop there? With a Pentax Q, your standard 135mm telephoto becomes a 756mm-equivalent super-tele! Your 200mm becomes an 1120mm-equivalent! With just a 400mm you can take photos of the moon that will fill the whole frame[0]!

On the other hand - with a smaller sensor you get worse low-light performance, increased noise, poorer resolution, a greater difficulty with diffraction limit degrading your resolution[1], and decreased ability to isolate a subject. In technical terms, bigger sensors are where it's at.

It's certainly true that smaller sensors let you get more reach out of a piece of glass - but it's always funny that M4/3 is raised as the "ideal" format for doing this somehow, as if APS-C is not already smaller than full frame, or that there do not exist even smaller sensors which can give you even more reach.

Mirrorless bodies like the NEX system that let you cram big sensors into a small body size are definitely one of the more interesting developments recently. Especially the Fuji/Hasselblad collaboration that puts a digital medium-format sensor into a MILC body. The Fuji X-series are very interesting and well-designed cameras and I can't wait to see what they come up with next.

When I go on vacation I take an Olympus XA and a Fuji GS 645 folding camera for a nice combination of fields-of-view in a compact size. But at this point I'm really ogling the Fuji X-series...

[0] I've done this, uncropped photo with slightly missed focus: http://i.imgur.com/oFpu8JE.jpg

[1] Small sensors like M4/3 need to produce enough resolution to saturate their sensor at an extremely wide aperture, roughly by f/4 or so for a 16 mp sensor: http://www.cambridgeincolour.com/tutorials/diffraction-photo...

[jdietrich]

It's a question of balancing the tradeoffs of sensor size. For most photographers, the sweet spot is somewhere between APS-C and full frame. M4/3 isn't the ideal format, but it's a useful format.

The Olympus E-M1 MkII is fairly competitive with APS-C sensors, but you get significantly more reach. For most photographers, that extra reach is neither here nor there. The extra depth of field of a smaller sensor is more hindrance than help in a lot of cases. If you're a wildlife photographer who normally shoots with very long lenses, it's a compelling advantage.

[alistairSH]

While the lens would be lighter than a DSLR equivalent, I still can't bring myself to buy one for my Olympus set-up.

The reason I sold my Canon gear and went MFT was the size - it's almost pocketable and easily fits in a small backpack when travelling. Adding even a moderate telephoto ruins it for me.

[paulmd]

The focal ranges are more intended for APS-C, but do check out the Sigma 19/2.8 and 30/2.8 lenses. They are not quite a pancake lens, but they are pretty close.

Are you OK with manual glass? If so, check out the Samyang 135mm f/2. If that's still too big, the Pentax 135mm f/2.5 or Nikkor 105/2.5 are both quite compact (roughly the size of a can of soda) and will provide you with a little more reach. None of those is a native M4/3 lens, so you will need to buy them in a Nikon or Pentax mount and use an adapter.