Comparison of top left corners. The 9-18mm lens was on an Olympus E-M5, an the 12-40mm lens was on an Olympus E-P5.
The M.Zuiko 9-18mm is a decent lens, but the corners are a little bit on the soft side.
Now for normal viewing purposes, does it really matter? You’d have to blow up your photo to a very large size and look at the corners to notice. Nevertheless, when I look at the images at 100% in Adobe Photoshop, the corners are not very satisfying.
As you can see, the 12-40mm is much sharper in the corner, although I should point out it’s still not perfect. There is quite a bit of lateral CA at the corner that has been removed with the “Remove Chromatic Aberration” checkbox in Adobe Camera Raw, but the removal has left behind a halo around the brick structure (which I believe is a ventilation shaft for the Lincoln Tunnel). Earlier today, I praised the sharpness of this lens at 13mm, so in the future I need to test whether the lens gets any shaper if you zoom in by 1mm. [See update below.]
Nevertheless, until now the 9-18mm was the best lens I had if I wanted to take a picture wider than 17mm, but going forward the 12-40mm will be my go-to lens for focal lengths between 12mm and 16mm when I’m looking for the sharpest images. However, the 9-18mm still offers the benefit of being much smaller and lighter, and zooming into the ultra-wide range of 9-11mm.
Sharpness in the extreme upper-left corner is the same no matter what focal length I use (in the 12-18mm range).
I took the same picture again, and added some extra “Smart Sharpen” filter in Adobe Photoshop, and I think this do-over looks sharper. I used a wider aperture for the do-over. Believe it or not, on this lens the corners seem to be less sharp when you use apertures higher than f/4.0!
I think that’s a truly excellent performance for the extreme corner at the widest focal length of a zoom lens. Most zoom lenses tend to have much worse corners at the widest zoom. Is there any other 24-XXmm equivalent focal length zoom lens that has sharper corners at the 24mm-equivalent focal length? I don’t think so.