I heard that all mirrorless cameras (at the moment at least) use contrast AF. Does this mean that they will be inferior to DSLRs when it comes to fast moving objects (at least until something change regarding mirror less technology).
If this is the case, it´s quite easy to chose between mirrorless or DSLR for me for my next camera. The small size is nice, but lack of long range lenses and slower AF is deal breaker then.
Kristoffer, can I ask why you ask this question? I presume it's because you are still considering which camera system to buy into for birding (correct me if I'm wrong?).
From my personal perspective the whole issue around smaller/mirror-less camera bodies (for birding) is a bit of a non-starter from my personal experience. It might be possible to save around 500g from a camera body by not using a mirror/prism in the design (compare something like the Panasonic G1 with a Canon 40D for example), but when you put this weight saving in perspective by factoring in all the other bits & pieces that bird photographers generally carry (lenses, spare batteries, bags, tripods, etc, and of course other birding gear like bins & scope) even when travelling light, that extra weight makes very little difference overall.
No matter which system you use the biggest single difference to weight will be the lenses; you simply cannot get away from the fact that larger aperture lenses are bigger and heavier (but because of this increased size, image quality will usually be better, especially in difficult conditions such as low light, fast moving subject etc).
Coming back to the G1 & 40D example used above. You could theoretically, and by using the relevant adapters, fit something like an Olympus 300mm f2.8 to the G1, and it would weigh very similar to the 40D and Canon 300mm f2.8. Actually the Canon system would be a bit lighter because the lens on its own is lighter than the equivalent Olympus lens. It would no-doubt also handle much better in use.
I think what this comes down to is if you want a camera system that will get you good results under typical birding conditions, go with what's tried and tested, and in most cases that means Canon or Nikon, usually because they have the lenses best suited to this type of work.
There are good reasons why you don't see many excellent bird images from Olympus & Panasonic m4/3 bodies with their smaller lenses (of course excluding the excellent G1 digiscoped images that we see here on BF). I eagerly await their forthcoming 100-300 zoom (Panasonic), but would be
very surprised if it can match some of the bigger 'birding lenses' for image quality.
Now if you weren't talking about a system for birding then I can see a real advantage to mirror-less cameras. DSLRs are afterall a throw-back to old film technology, and we no longer
need camera bodies with mirrors & prisms, but I think we will have a while to wait yet before we completely move away from this type of design. Canon & Nikon at the moment don't even seem interested in competing on this playing field, though no-doubt they will be keeping a very close eye on developments of this kind.
Steve