There has been a lot written about the importance, or not, of sharpness and other quality measures of lenses. The ridiculous thing about this is often only measurable differences are discussed, rarely actual real world differences. Reviewer who shun test charts have to take a different direction when reviewing, often feeling they have to be excused for their less than technical methods.
A case in point is the 17mm Olympus lens. I have been a grudging user then a fully converted fan of this lens. Like many others, I find the using of it far more satisfying than reading it's reviews. Are there better lenses? Always. Are there lenses more suited to the tasks this lens is intended for? Not many.
First lets put the quality issue into some context.
Wide-open lens performance is a much loved and measured characteristic of the modern era. With M43 lenses it is more relevant than other formats, because offering more depth of field than any larger formats at an equivalent focal length, the format tends to have it's wider apertures hammered.
There are technically better lenses than the 17mm when a wider aperture is used, no doubt. Is it atrocious? No, but it is soft on the outer frame and suffers from some obvious CA issues. I also find the lens tends to wash out highlights, lowering contrast a bit at wider apertures, especially on the EM5.
So, what does this really mean?
If you shoot wide open in the corners and print very large prints, you will have to do some selective sharpening and CA removal. That's it. How much better or worse would lens "X" be to this? Hard to say and the only way a viewer could possibly know is if you placed two of the same print taken with different lenses side by side. Not a real world scenario. This is another case of "Go find me a problem. Now find me a real problem".
Is there a bright side to it's performance?
Yes there is. The transition from focussed to out of focus with this lens is extremely coherent, or elongated (?). In practical terms, you can shoot wide open when you need to, with the image holding on to out of focus detail better than many "modern" bokeh lenses. Modern bokeh, as I call it, is a lens design that exaggerates smoothness and fast drop off for good portrait separation, very "on trend" at the moment and ideal when relevant. In a wide standard lens it is not really relevant.
The proper use of this focal length is environmental portraiture, not head shots. With an environmental portrait, coherent surroundings, even if they cannot be fully in focus due to other considerations is far more important that smooth mush without story telling potential.
Possibly one of the benefits of the slightly softer, lower contrast rendering wide open is it does not highlight out of focus regions against in focus ones too obviously. Remember, the Japanese have long worshipped the German lens makers of old. Many modern Japanese designs emulate or copy styles and principles of older lenses for good reason. The old joke used to be the Japanese design lenses for us, while they use lenses made by Germans.
Sharpness stopped down evens the field. When needed for landscape or deep street scenes, from f2.8 to f8, the lens shows much the same characteristics as it's major competition (Leica 15mm, Lumix 20mm and 14mm, Sigma 19mm).
It is important to remember, that many of the best M43 lenses are less than perfect here.
So, to sum up, is it really any good?
It is nearly ideal for the task it is designed for. The designers took a risk with this one, hoping, I feel, that the public would get what they were aiming for and not let the test bench brigade beat it up too much. The big risk is the review reader jumping at another lens and finding the measured optical benefits are a poor substitute for the excellent handling and practicality of the design.
Lately I have taken mine off the Pen F and mounted it on an EPM2 body. The camera uses the same sensor and processor as the EM10 mk1, offering quality as good as any in the first generation of 16mp Olympus cameras, i.e. plenty. The handling suits the lens perfectly. The camera can be in my off hand (left) and I can turn it on, focus and shoot without making the operation obvious.