12mm vs. 12mm - 50mm
I do have the 12-50 and had the 12mm for a short while. Usually I take pictures with the 20mm and 45mm. Yesterday I had the opportunity to walk around a bit with the 12-50 since I had the same question: would 12mm be wide and good enough?
I originally took the 12-50 since it was affordable and since I started out from scratch with mFT. From a feature set point of view the 12-50 sounded not to bad for the money: good video support, 12mm, macro, fast AF, silent, water resistent. Maybe even the only lens my wife would ever care to use on the E-M5.
Returning home from yesterdays trip I have to admit that I am not too fond of the results. It was a sunny day and quite some of the images miss a bit of contrast. Combined with the limited sharpness the lens produces (sure wide is somewhat better than tele) this gives very often the appearance as if there is some haze over the image. I reviewed quite some images through most focal lengths and apertures (max. 8). I even tried some quick macro but ultimately it shows pretty much the same behaviour. I did want to know if this is due to the bright sunshine so I did an indoor shot today and compared it with a shot from the 20mm. Same effect here but maybe not that strong: the 20mm image simply pops due to sharpness but as well due to contrast.
Surely you can push in postprocessing and you will get printable results but at least to my taste this is somewhat below my personal quality limit.
The 12mm had the pop & clarity but unfortunately not the sharpness I would imagine from a 630 EUR lens towards the borders. Maybe sample variation or maybe just to high expectations on my end but since I do still have an old 5D system I did compare with the 24-105L IS zoom and it simply blows the 12mm out of the water when stopped down and similarly corrected in Lightroom. Again, your milage will vary but to me this is not worth the 630 EUR. Maybe I check out another sample of the 12mm.
I would say the 12-50 is nothing for a critical photographer. It is a convenient lens for some but even though I could postprocess its results into something which would look good in web size ultimately this is not for me.
One alternative would be the Panasonic 14mm. This might not be the sharpest lens in the corners (and some would prefer a good 14-xx kit from Panasonic) but at least the results look pretty clear to me, aperture 2.5 is something and of course it has minimum size. Combined with 20mm and 45mm you have a pretty nice, cost efficient and usable small setup.
Since I am the wide guy I will check out the Panasonic 7-14 anyway but this is so outside the budget if the 12mm already is.
After having some idea how the E-M5 and some lenses compare to my old 5D MK I I came to the conclusion that for my needs the E-M5 might just stay as a small, silent, unobstrusive system with good but affordable lenses such as 14, 20, 45. This is what it does incredibly well.