That comparison featured an image without any highlights in the out of focus background. This time around, I figured I would try a high contrast night exposure, with bright highlights out of focus. Again, I set ISO 160 on the Panasonic GH2. The camera was on a tripod, and the exposures lasted around 1-8 seconds.
Here are the full images from both lenses:
Lumix G 14mm @ f/2.5
Lumix G 14-42mm @ 14mm f/3.5
The focus was set on the post to the left, which is around 30cm from the camera, close to the minimum focus distance for these lenses. I used the A (aperture) exposure mode.
To evaluate the bokeh, let's enlarge some of the areas from the image.
From the centre of the image:
And from the top of the image:
(Click for larger images.)
I think the bokeh from both lenses is a bit "dirty" and "swirly". The 14mm pancake lens has the most ringing in the out of focus rendering.
My conclusion, which is a bit unexpected, is that the zoom lens has the best bokeh. Or perhaps it is better to say it has the least displeasing bokeh, since neither are very good. But the difference is small.
The 14mm pancake lens has non-circular bokeh even at the largest aperture, which is not so usual. The Lumix 20mm f/1.7 pancake lens also exhibits non-round bokeh. So perhaps it is related to the pancake design?
Keep in mind that these enlarged images are 100% views from the 16 megapixel GH2 sensor. most people will probably downscale the image some, in which case the dirtiness and ringing of the bokeh becomes a smaller issue.
Also, bokeh and wide angle is not that much of an issue anyway. To get some out of focus rendering at 14mm focal length, I had to focus close to the minimum distance, and look at objects in the far background. It is not so likely that you'll find the same situation in real life.
For example, if you're photographing people, you'll want to keep then at a distance of around 1 meter or more, to avoid perspective distortion. At this focus distance, you're unlikely to see much bokeh with a 14mm lens, even at f/2.5.
So even if the bokeh for these lenses at 14mm could have been better, you should not see it as a fatal problem. It is, at worst, a minor annoyance for some types of images.