As you probably well know, I have strong feeling s about bokeh (or Boke Aji) and it's best application with my various lenses.
Yesterday I used the Pen F and 12-40 for some street images and re discovered why I usually do not use that kit, that way.
Both of the images were taken at 14mm with focus fixed at a little over 1m (nothing between 1 and 5 meters, so it's hard to tell), f7.1 (thats about 28mm and f13 on a full frame!) and there was enough light to guarantee a reasonably fast shutter speed. The focus drop off is so fast with this lens, that even subjects slightly out of focus are soft. After using the 17mm for a while now, this is really off putting. I know that at f2.8 the 17mm will give me a gradual and acceptable focus transition. It gives me confidence and allows me to take images that would otherwise push the camera impossibly. It looks as though I have two lenses at the extreme ends of the range when it comes to focus draw.
The issue may be incorrect barrel markings on the lens, and the markings are a lot sparser than the 17mm's, but even so, the drop off is severe, but nice for portraits.
This snap of a dejected Jack as we were leaving is at f2.8 (af lock on) and 35mm. Pleasantly the DOF looks to be from a bigger camera, but his eyes are a little out and three previous images were unusable.
Another taken at f7.1 and 38mm (f13 and 75mm full frame). The subject was about a meter away and the image is not cropped. The foreground and background leaves are all slightly out of focus. The ones in the middle where focus landed are nice and sharp. Not crazy 75mm sharp, but smooth sharp*.
Is this a problem?
It is something to aware of and explains why I have had a luke warm reaction to lens. Between very unforgiving focus drop off and a pleasant but not biting sharpness in it's sweet zone, the lens can frustrate. I am intending to use it for landscapes, as a second to my 40-150, that will get a lot more work and should be able to work well enough with it, but for street, I cannot be bothered with better options (17mm and 14-42 kit) available.
On the bright side, Olympus have been able to supply a f2.8 pro lens on a larger sensor look, and real f2.8 benefits at the same time.
*Another thing to ponder is the sharpness types Olympus have offered in their range.
The pro zoom has a smoothness that is ideal for it's type, giving both the lens and the camera the benefit of it's rendering. The 17mm is more "gritty" sharp and simply clear, using lots of micro contrast to (possibly) help it's bokeh and to suit it's street subject matter. The 75mm is just razor sharp with great drop off for portraits.