The fact is that all those lenses I have ever used have performed very much like a toy lens when used wide open. The centres might be sharp, but image quality falls away as we progress down that diagonal line from the centre of the frame to the corner, and we get to enjoy vignetting, dropped focus and occasionally the swirling madness of coma distortions – not to mention the break up of contrasty edges into a neon cocktail of green/cyan chromatic fringing.
Technically, these lenses have been poor, requiring the expensive iris to be closed to f/4 or f/5.6 before a respectable performance can be achieved – although, of course, it is easy to forget that this is their charm. For a centrally placed subject and a desire to draw a focused eye from the page in glorious 3D effect, these characteristics are heaven-sent.
With the benefit of a smaller imaging area, the micro four thirds system has the opportunity to create the classic shallow depth-of-field effect with a focal length that is much easier to make well. And when we double the focal length of this new 42.5mm lens according to the 2x magnification of the four thirds system, we find we have the same view as that achieved by the legendary 85mm.
However, making a super-fast 42.5mm lens involves many fewer compromises than the design and construction of the longer focal length demands. Read the rest of this review on the Amateur Photographer website