Canon explains why they still don't have a professional mirrorless camera | Photo Rumors Not bad, not bad. But the third IMHO would be the angle of incidence issue. One of the prime benefits of having a mirrorless camera is that the distance between sensor and lens can be much smaller. This in principle allows simpler, shorter, more lightweight, higher quality and cheaper wide angle lenses, that do not need to be constructed as retrofocus. But to fully exploit this advantage, the sensor has to be able to handle light with steep angles of incidence. And finally, of course there is also battery life.