Quote:
Originally Posted by inkista
The reason 50mm are so prevalent and cheap is that back in the days of film rangefinders and film SLRs, 50mm was normal, and a 50/1.8 or 50/2 was the kit lens you got with the camera. Every SLR lens maker out there has been creating 50mm lenses since the 1930s, and they've had decades to learn how to produce good ones for cheap.
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To add to the above:
Most 35mm SLRs had flange-to-film distances of 40-45mm or so. A 50mm lens could be produced that sat effectively 50mm from the film. That meant that the lens could be built as a simple Gaussian design, without any telephoto or retrofocal lens groups that would complicate the lens, increase the cost, and reduce the image quality.
With the 4/3 system, the flange-to-sensor distance is still about 39mm. A "normal" lens of around 25mm needs a fairly powerful retrofocal lens group to get it to focus 39mm away. That retrofocal group raises the cost and reduces the image quality.
As for 50mm lenses specifically, the other manufacturers chose to make their DSLRs compatible with their older lenses. Olympus chose to design an entirely new lens mount and series of digital lenses, so there aren't any old 50mm 4/3 lenses hanging around from the film days.
One of the features of micro-4/3 is a reduced flange-to-sensor distance of a bit over 19mm. It should be possible to make a 25mm "normal" lens with a simple Gaussian design for micro-4/3. It seems that nobody has chosen to do so (yet).