08-12-2014, 01:01 PM
Quote:I do think f1.8 for 9mm makes sense for a MFT lens. Usually the sweet spot of a lens is reached after stopping down about 2 stops from the maximum aperture. If the maximum aperture is f1.8 then the sweet spot would be around f2.8-f4, just corresponding to f5.6-f8 for a FF lens. If the maximum aperture is f2.8 then the sweet spot would be around f5.6-f8 but then diffraction already comes in for MFT.
In fact I think all primes for MFT should start the aperture from at least f2.
Not necessarily. Some MFT lenses like the 12-40 don't really improve by stopping down (pretty much the same from f/2.8 to f/5.6 at all focal lengths).
If well designed, a 9mm f/2.8 could very well be at its best wide-open.