Andy Westlake puts an inexpensive fast normal prime lens for Micro Four Thirds cameras to the test.
Panasonic Lumix G 25mm f/1.7 Asph – Autofocus
As we’ve become used to from Panasonic, the lens focuses quickly, silently and decisively, thanks largely to its internal focus design. With the latest cameras, it will also continue to do so in remarkably low light without hunting back and forth for focus position. Notably, it’s much faster at autofocusing than Panasonic’s 20mm f/1.7 pancake, which is a six-year-old design. The focus-by-wire manual-focus system is likewise responsive and straightforward to operate.
Autofocus is, in the grand scheme of things, very accurate, regardless of whereabouts in the frame the focus area is positioned. However, during the course of my testing I came across a slight catch; the lens’s plane of sharp focus shifts forwards fractionally on stopping down, which is a symptom of residual spherical aberration. Because Micro Four Thirds cameras normally focus with the aperture set wide open, this can result in the edge being taken off the sharpness when you’re shooting at f/2.8, particularly with close-up subjects. However, while this effect was easily measurable in our studio testing of the lens, it’s not something many users are likely to notice during normal shooting.