Lumix G 14mm f/2.5 pancake
Lumix G 14-42mm f/3.5-5.6 Mega O.I.S.
Lumix G HD 14-140mm f/4-5.8 Mega O.I.S.
I did the comparison by taking the same photo with all three lenses, at various apertures. The pictures were taken with the Panasonic Lumix GH2 camera on a tripod, at ISO 200. I used the self timer to avoid camera shake during the exposure, and disabled image stabilization. The pictures below were rescaled and sharpened. Here they are:
14mm pancake @ f/2.5
14-42mm @ 14mm f/3.5
14-140mm @ 14mm f/4.0
Field of view
These lenses are specified to 75° field of view at 14mm focal length. We see from the example images that the field of view is very consistent. You will notice some changes in the perspective for close objects. This is due to the physical length of the lenses, which varies, with the pancake obviously being the shortest lens.
A closer examination
To better be able to compare the bokeh and sharpness of the lenses, I have looked at 100% crops from the same area of each image. These images have not been scaled or sharpened. Click for a larger version.
The bokeh (out of focus rendering) is pretty similar for all three lenses. When ranking them, I would put the 14mm pancake first, then the 14-42mm zoom, and finally the 14-140mm superzoom. But the differences are small, indeed.
Note that in this case, I am focusing on near infinity, and looking at the bokeh of near objects. It could be that the nature of the bokeh of far objects when focusing on a near object is different. So more tests are certainly needed to make a perfect conclusion.
If you are interested in getting nice bokeh, these are not the right lenses to choose, anyway. Longer lenses are better, if you are interested in keeping some parts of the image out of focus. I would recommend the Lumix G 45-200mm f/4-5.6 value tele zoom for this application. An even better, and more expensive choice, is the Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro. (It seems that the longer the name, the higher the price.)
When it comes to flare handling, though, it seems that the Lumix G 14mm f/2.5 pancake handles it the best. This is probably due to it's simpler optical design: It only comprises six lens elements. Generally, the fewer lens elements, the better it handles flare. Of course, there may very well be exceptions to this general rule.
To my surprise, I note that the basic kit lens Lumix G 14-42mm f/3.5-5.6 Mega O.I.S. is sharper than the very expensive Lumix G HD 14-140mm f/4-5.8 Mega O.I.S. at f/4, and even at f/3.5. The superzoom lens does sharpen up a lot when stopped down to f/5.6, though.
I'm thinking the tripod might have been accidentally shaked during the 14-140mm f/4 exposure. I should revert to this later to check if that might explain the unexpected softness. On the other hand, it is a well known fact that the 14-140mm zoom is a bit dull in the wide and long ends.
The Lumix G 14mm f/2.5 pancake lens is quite sharp at max aperture, and appears to reach it's sharpest around f/5.6, which is quite common for this type of lens.
Here are some alternative crops from the same images. The are from the middle, right border of the image.
There is some passing traffic which makes the lightning a bit different. This is unfortunate, but no big problem in the comparison. Also, some wind is affecting the tree.
Here's another set of 100% views, from the left hand border of the image:
The conclusions are pretty much the same as from the other images. We can see that the Lumix G 14mm f/2.5 pancake lens is somewhat less sharp at f/2.5, compared with the centre. But it sharpens up when stopping down to f/2.8. Overall, I am pretty happy with the sharpness of the pancake lens.
In the last image, we can also note that the borders are a bit darker due to vignetting. This is an issue mostly when the lens is wide open. When closing down about one stop, the problem goes away.
The Lumix G 14mm f/2.5 pancake appears to be an adequate lens in all these tests. It has some vignetting wide open, and it is not tack sharp wide open. The bokeh could conceivably have been better. But all in all, it is a good lens.
You should probably not buy the 14mm pancake lens for the ultimate optical performance, but rather for the compact size, stealthy appearance, and fast autofocus. Add a bit of cuteness factor, and it becomes a tempting buy. Here is another test of the optical qualities of the Lumix 14mm pancake lens.
The Lumix G 14-42mm f/3.5-5.6 Mega O.I.S. appears to be a competent lens. While this lens has received a somewhat poor welcome by fans online, I find it to be good. It also has consistently fast autofocus.
People who buy this lens in a camera kit, and are eager to unload it in an online auction should consider to think twice. While it remains a basic kit lens, it can be appreciated for the compact size, lightness, and adequate optical performance. There can be many cases when you'll want to use a small, light kit zoom lens.
Our most expensive lens, the Lumix G HD 14-140mm f/4-5.8 Mega O.I.S., disappoints in this test. While I am doubting the results at 14mm f/4 a bit, it is a well known fact that this lens is a bit unsharp in the wide and long ends of the zoom. You shouldn't toss it based on this test, but keep in mind that it excels in terms of sharpness in the focal range between the extreme wide and longest end.
My test subject here was far from optimal. However, with the dark and cold winter, I was a bit out of inspiration, and didn't want to lug the gear around too far in -10°C.