The lens' sweet spot seems to be between f2.8 and f11. Below f2.8 it shows a slight propensity for chromatic aberration and it doesn't attain optimum sharpness until there -- though it's still quite acceptable -- and sharpness declines a bit between f8 and f11. I was very disappointed with f22, however, which I found simply too soft to use. This pattern applies to both center and corner sharpness, as it's pretty consistent edge-to-edge.
|Mount||Micro Four Thirds|
|Aperture range||f1.8 - f22|
|Minimum focus distance||33.1 inches|
|Angle of view||16 degrees|
|Elements||10 elements in 9 groups
3 extra-low dispersion lenses,
2 high refraction lenses
|Lens barrel diameter||2.7 inches|
|Lens length (min/max)||3 inches|
Overall, the lens is quite bright, with no discernible vignetting and minimal distortion, produces beautifully soft out-of-focus areas, and the coating seems to do a great job of minimizing flare. The iris renders lovely round highlights.
I'm not a big telephoto shooter -- my range is more 24mm-90mm (35mm equivalent) -- and I tend to get frustrated by lenses that don't focus closer than a foot, though I realize there are technical reasons why lots of lenses don't focus closely. So while I hate that this lens can't focus closer than almost 3 feet, it actually fares better on that front than a lot of comparable-length lenses.
Until this lens arrived, there were no telephoto primes for Micro Four Thirds cameras, and certainly nothing this fast at a comparable focal length in a zoom. But it's gratifying that despite being the only current option, it's still a good one.