Lumix tele lenses compared

Panasonic makes an impressive number of tele zoom lenses. This is not a stupid choice, after all, the interchangeable system camera market relies on the consumer actually buying the extra lenses. So there needs to be some lenses to choose from. And a tele zoom lens is a popular aftermarket choice, probably the most popular together with a fast prime lens.

In this article, I will be comparing six of them:

Lumix 14-140mm OIS jitter?

I really like the Lumix G 14-140mm f/3.5-5.6 superzoom lens (click for my review). Compared with the older version of the lens, I find that it is better in every way: Smaller, lighter, cheaper, better image quality. So what is not to like?

There are some who say that the new version of the lens causes "micro jitters" when recording video handheld, which makes it impossible for use with video. As the lens is advertized for video use especially, this sounds like a very bad thing.

To test if there is merit to the claim, I have tried to put both lenses (the new and old version) on the same camera, Lumix GX7, and recorded video at 1080p, 50FPS. To avoid motion blur, which might hide the micro jitters, I set a fast shutter speed at 1/200s.

Both cameras were connected to a Desmond mini stereo bracket. The new version of the lens to the left.

Lens disappointment, Lumix G HD 14-140mm

Normally, I write the most about the lenses I like the most. I guess this is partly natural, to write about what is positive, and also reflecting my nature. But, this time, for a change, I write about a lens that has disappointed me: The Lumix G HD 14-140mm f/4-5.8.

To put it shortly, I think this lens has failed to live up to the promise: It is not very sharp, with the exception of the middle of the zoom range. Also, it does not focus faster than the other, and much cheaper, zoom lenses, nor does it operate less loudly, both of which were the claims of the "HD" branding.

The lens was originally launched in 2009, and for the first period only sold in a kit with the Panasonic GH1. It was marketed as a video optimized superzoom lens, and said to have a very quiet, accurate aperture mechanism, capable of near stepless changes. Some have said that the aperture can change in 1/6th stop steps.

It is fairly well known and agreed that the lens is dull in the long end. To further make this claim more credible, here is a comparion of the sharpness at 100mm, where significantly less expensive lenses come out much better. In this test, I am comparing the lens to the Lumix G 14-42mm f/3.5-5.6 and the Lumix G 14mm f/2.5 pancake lenses at 14mm, and conclude that both of the latter are significantly better. So in my experience, the 14-140mm lens only really shines in the middle of the zoom range.

When measuring the autofocus noise, the lens comes out at a fairly average level, comparable with all the other zoom lenses. Also, the aperture change noise was measured to be at a higher level than the other zoom lenses, not really any impressive. This suggests that the HD designation of the lens is rather worthless, as non-HD lenses perform as well, or even better.

The aperture range of the lens is also not so impressive, f/4-5.8. Competing superzoom lenses tend to have the aperture range f/3.5-5.6. Also, when looking at the aperture as a function of the focal length range, you'll see that it very quickly goes up to f/5.8:



Given these experiences, it is perhaps only fair that this lens is now rumoured to get a makeover. A picture of a new version of the lens has been seen. The new lens retains the same basic specifications, but is smaller, with a 58mm front lens thread. The original lens has a 62mm lens thread. The 58mm front lens thread is the same as is used on the Lumix X 12-35mm f/2.8 and Lumix X 35-100mm f/2.8 pro spec zooms.

Since making the original 14-140mm lens, Panasonic has come a long way. The new X branded f/2.8 zooms are very good, and I am sure that with this experience, Panasonic can design a much better 14-140mm lens.

Since writing this article, the new lens has been announced, and it has the more attractive aperture range of f/3.5-5.6, in additon to being smaller and lighter. I would definitively go for the new version, if I had the choice now.

Geometric distortion correction

Most of the Micro Four Thirds lenses need geometric distortion correction applied for the output images to become rectilinear. This is done totally seamlessly by the camera and software, both for JPEG and RAW images. So the user never notices that the image, as seen by the camera through the lens, is not rectilinear in the first place.

This is in contrast to older DSLR systems. In these systems, there is an optical viewfinder, in which the users sees exactly what the sensor sees, through the lens. With a DSLR system, the lens must be rectilinear, otherwise, the user will be appalled by the geometric distortion when using the camera.

Here is an illustration of two basic kinds of distortion: Pincushion distortion (left) and barrel distortion (right):

In reality, the geometric distortion might very well be more complicated than what is illustrated by these simple models.

I have previously tested the geometric distortion properties of some Micro Four Thirds lenses, and I found that virtually all lenses featured some distortion correction. Especially wide angle lenses, or the wide end of zoom lenses. Since this time, I have acquired some new lenses, and I wanted to test them in the same way.

Again, I have done the tests by taking a pictures of a tiled wall. The images look like this:

Since I am only interested in the geometric distortion, I have increased the contrast so that the images become monochrome. I also superimposed the corrected out of camera JPEG images (black) onto the original RAW uncorrected images (red).

I included the appropriate adjustment needed. The adjustment numbers in percent refer to the "Lens Distortion" filter in The Gimp, an image processing software. Of course, to become rectilinear, some lenses might require more complicated adjustment than the simple model given by the "Lens Distortion" filter. So these figures are just intended to be approximate relative indicators of the degree of distortion. A positive figure indicated barrel distortion, while a negative figure indicates pincushion distortion.

Here is a comparison of the uncorrected and corrected images for some lenses.

Panasonic Lumix 14mm f/2.5 pancake: -16%

There is a significant barrel distortion, which is corrected in the in-camera JPEG image. However, there is some residual barrel distortion even in the corrected image. I have noticed this previously. In fact, the lens is rectilinear (after correction) at long focus distances, but has some barrel distortion at close focus distances. In this example, we see the barrel distortion at close focus distance. This is not an uncommon behavior for lenses that feature internal focus.

Olympus M.ZD 45mm f/1.8: 0%

No distortion correction at all. It looks like there is a small amount of pincushion distortion, though, so perhaps there should have been some in-camera correction done by the camera.

Panasonic X PZ 45-175mm f/4-5.6 @ 45mm: 0%

No distortion correction at 45mm.

Panasonic X PZ 45-175mm f/4-5.6 @ 100mm: +5%

There is some pincushion distortion correction at 100mm, but not a lot.

Panasonic G 100-300mm f/4-5.6 @ 100mm: 0%

No geometric distortion correction at 100mm.

Summary

Including the results from my previous study, I can present a table with the relative distortion corrections of various lenses:

Lens	Focal length	Relative distortion correction
Lumix G 20mm f/1.7 Pancake	20mm	-11%
Lumix G 14mm f/2.5 Pancake	14mm	-16%
Lumix G 14-42mm f/3.5-5.6	14mm	-18%
Lumix G 14-42mm f/3.5-5.6	30mm	0%
Lumix G 7-14mm f/4	7mm	-17%
Lumix G HD 14-140mm f/4-5.8	14mm	-17%
Lumix G HD 14-140mm f/4-5.8	30mm	-4%
Lumix G 45-200mm f/4-5.6	45mm	+1%
Lumix X PZ 45-175mm f/4-5.6	45mm	0%
Lumix X PZ 45-175mm f/4-5.6	100mm	+5%
Lumix G 100-300mm f/4-5.6	100mm	0%
Olympus M.ZD 45mm f/1.8	45mm	0%
Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro	45mm	0%
Lumix 8mm f/3.5 fisheye	8mm	0%
Sigma 30mm f/2.8	8mm	0%

Conclusion

We see that wide angle lenses and zooms typically feature barrel distortion (negative figure) in the wide end. On the other hand, longer lenses are often not corrected, or are corrected for a small amount of pincushion distortion (positive figure). The in-camera distortion correction is some times insufficient, for example we've seen that the Olympus M.ZD 45mm f/1.8 and Lumix G 14mm f/2.5 pancake lenses feature some geometric distortion in the short focus range, while behaving better at infinity focus.

There are some who have speculated that Leica-branded lenses are not subject to any software corrections. I have looked at the Panasonic Leica 45mm f/2.8 1:1 macro lens, and found no indications of software adjustments to the images. However, I still don't believe that statement. One of the first cameras for which the software corrections were widely discussed online, was the Panasonic Lumix LX3 high end pocked camera from 2008. And it does feature a Leica-branded lens, and quite clearly, there is a significant barrel distortion in the wide end of the zoom, which is corrected by software.

Sharpness comparisons @ 100mm and 200mm

Panasonic has got several Micro Four Thirds lenses that span the tele focus range, with the Lumix G 45-200mm f/4-5.6, Lumix G HD 14-140mm f/4-5.8, and Lumix G 100-300mm f/4-5.6 being three of them. The last one is the recently announced powerzoom capable Lumix X PZ 45-175mm f/4-5.6.

The Lumix G 45-200mm f/4-5.6 is a value tele zoom lens, with a useful focus range reaching from the typical portait to long tele area. It gives a good value for money for those who want to try out the tele range.

Marketed as a video optimized lens, the Lumix G HD 14-140mm f/4-5.8 is in fact versatile superzoom lens for photo and video use alike. It is large, expensive, and generally regarded as being very good.

The largest of the three, the Lumix G 100-300mm f/4-5.6, is a very long tele zoom, useful for various event photography, like spectator sports, birdwatching, safari, and so on. For this use, the price is in fact rather reasonable.

The three lenses are seen below:

But how do their sharpness compare? To try to answer this, I've tried to compare them where they overlap. In this experiment, I put the camera on a sturdy tripod, shot at ISO 160 with the Panasonic GH2, and used a delayed shutter to avoid camera shake. I also turned off OIS. I set the white balance to "overcast" for all the images.

I left the exposure at auto at all time, and sadly, the exposure turned out to be slightly different for some of the images. That's a bit negative for this comparison, but I think we can live with it.

Sharpness at 100mm

Here are the full images shot at 100mm, scaled down and sharpened. Click for larger images.

Lumix 45-200 @ 100mm f/4.7	Lumix 100-300 @ 100mm f/4	Lumix 14-140mm @ 100mm f/5.8

To better compare the sharpness, let's look at 100% crops. I have not applied any sharpening to these 1:1 images. These are taken from the image center. Click for larger images.

As it was a bit windy, I recommend that you don't look at the leaves to evaluate the sharpness. They may be negatively affected by motion blur due to the wind.

Sharpness at 200mm

Here are the full images shot at 200mm, scaled down and sharpened. Click for larger images.

Lumix 45-200 @ 200mm f/5.6	Lumix 100-300 @ 200mm f/4.9

To better compare the sharpness, let's look at 100% crops. I have not applied any sharpening to these 1:1 images. These are taken from the image center. Click for larger images.

And from the top right corner:

Conclusion

Based on this study, it is quite clear that the Lumix G 100-300mm f/4-5.6 is the sharpest of the three lenses. It appears to be quite sharp even wide open. On the other hand, one could say that this is not surprising: It was used in the shorter end in this study, compared with the Lumix G 45-200mm f/4-5.6 which was used in the longer end of its zoom range. Also, the Lumix G 100-300mm lens has the lowest zoom ratio, which allows the designers to make less compromises.

The Lumix G HD 14-140mm f/4-5.8 disappoints a bit. But then again, it is a well known fact that it is not at its sharpest in the longer end, and 100mm is surely a long focal length for this lens.

The bokeh appears to be comparable between the 45-200mm lens and the 100-300mm lens. Perhaps one could say that the Lumix G 45-200mm is slightly more busy with the longer of these lenses, with some more "ringing" around the out of focus highlights. But they are pretty similar.

Geometric distortion correction

Many Micro Four Thirds lenses feature in-camera geometric distortion correction. Two examples are the Panasonic pancakes, Lumix G 14mm f/2.5 and Lumix G 20mm f/1.7. Both have pretty similar distortion correction needs. When converting the sensor output to the out of camera JPEG image, around 10% of the pixels in the border area are lost.

This is somewhat controversial. Some feel that a quality lens should not require further software correction. In fact, the lack of geometric distortion is a traditional sign of a high quality lens.

I think that this is mostly a non-issue. By allowing some aspects of the image to be adjusted in software, the lens designers can focus on issues which cannot be corrected in post processing. This has the potential of making the lenses better, at a smaller size, and potentially a smaller cost. Panasonic Micro Four Thirds lenses are adjusted for geometric distortion and some chromatic aberrations. The geometric distortion is also corrected in Olympus Micro Four Thirds cameras. At this time, though, Olympus does not correct chromatic aberrations.

To illustrate the geometric distortion done with various lenses, I have photographed a tiled wall with them, and shown the sensor output compared with the corrected JPEG output.

Here is an example pair from the Lumix G 20mm f/1.7 pancake lens:

uncorrected RAW output	JPEG image

Note that this is in no way a criticism of using RAW images. There are many RAW image converters which will do the distortion correction automatically and seamlessly, and you will never notice that there was any geometric adjustment done at all. I am using the RAW images to visualize the initial image captured by the sensor, as it is the only way to access it.

Here is a comparison of the uncorrected and corrected images for some lenses.  Since I am only interested in the geometric distortion, I have increased the contrast so that the images become monochrome.  I also superimposed the corrected out of camera images (black) onto the original uncorrected images (red).

I have also included the appropriate adjustment needed. The adjustment numbers in percent refers to the "Lens Distortion" filter in The Gimp.

Lumix G 20mm f/1.7: -11%

Lumix G 14mm f/2.5: -16%

Lumix G 14-42mm f/3.5-5.6 @ 14mm: -18%

Lumix G 14-42mm f/3.5-5.6 @ 30mm: 0%

Lumix G 14-140mm f/4-5.8 @ 14mm: -17%

Lumix G 14-140mm f/4-5.8 @ 30mm: -4%

Lumix G 45-200mm f/4-5.6 @ 45mm: +1%

Conclusion

Normal zoom lenses pretty consistently feature barrel distortion in the wide end. The tele zoom Lumix G 45-200mm appears to have some very small pincushion distortion, but very minor.

Some lenses that do not feature any geometric distortion correction are the Lumix 8mm f/3.5 fisheye and Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro lens.

AF speed, GH1 vs GH2

I have previously checked the AF speed of the Panasonic GH1, and the Panasonic GH2. However, the tests were done at different times, and with different setup, lightning, etc. Also, the GH1 firmware has been updated in the mean time. So I decided to check both cameras again, under exactly the same conditions.

Again, I set a LEGO figure in the centre of the image frame, and found the time from pressing the shutter release button to the camera taking the image. I turned on the camera just before testing the autofocus, which means that the focus is near infinity when first pressing the shutter release button.

I did the test under two different conditions. The first was in dim light, with a black background: There is artificial lights, and rather dim at around EV5. The distance from the camera to the LEGO figure was about 0.6m.

The second was with daylight coming in through the windows, and white background. The lightning was about EV9.

Here are a couple of examples:



Panasonic GH1, Lumix 20mm, dim lights, black background



Panasonic GH2, Lumix 20mm, dim lights, black background



Panasonic GH1, Lumix 14-140mm @ 140mm, daylight, white background



Panasonic GH2, Lumix 14-140mm @ 140mm, daylight, white background


And these are the timings I found:

Lens	GH1, dim	GH2, dim	GH1, daylight	GH2, daylight
Lumix G 14mm f/2.5 pancake	0.43 seconds	0.43 seconds	0.37 seconds	0.20 seconds
Lumix G 20mm f/1.7 pancake	0.57 seconds	0.53 seconds	0.53 seconds	0.40 seconds
Leica Lumix DG 45mm f/2.8 macro	1.07 seconds	0.93 seconds	0.73 seconds	0.43 seconds
Lumix G 14-42 @ 14mm	0.43 seconds	0.33 seconds	0.30 seconds	0.20 seconds
Lumix G 14-42 @ 42mm	0.47 seconds	0.40 seconds	0.37 seconds	0.20 seconds
Lumix G HD 14-140 @ 14mm	0.40 seconds	0.33 seconds	0.27 seconds	0.17 seconds
Lumix G HD 14-140 @ 50mm	0.53 seconds	0.57 seconds	0.40 seconds	0.23 seconds
Lumix G HD 14-140 @ 140mm	0.70 seconds	0.53 seconds	0.50 seconds	0.33 seconds

What we see here, is that the timings are remarkably similar in the tests done with dim lights. The GH2 has a small advantage to the GH1, especially with the fast focusing zoom lenses. But in this test condition, there is little to gain by using the GH2.

On the other hand, when testing the cameras with more light available, the difference is larger. The GH2 really excels in this test condition.

My previous test gave a larger difference between the two cameras. However, the GH1 firmware has been upgraded several times since that test, and so has the lens firmware. It seems that the GH1, with the up to date firmware, is still very capable.

As for the accuracy of the focus, it is very good with both the GH1 and GH2. Both cameras use CDAF (contrast detection autofocus). This means that the image sensor checks the actual image for focus before the camera takes the picture.

In contrast to SLR cameras, which use PDAF (phase detection autofocus). This means that there are separate AF sensors behind the mirror, which check the focus in some spots in the frame. These sensors must be calibrated to the image sensor, a process which is costly and complicated. Users of SLR cameras often worry that the camera/lens combination is back-focusing or front-focusing, i.e., that the AF sensors are noe correctly calibrated. This is something that users of Micro Four Thirds don't need to worry about.

Modern DSLRs can also use CDAF, which is generally refered to as "live view". However, this focus mode is often quite slow on DSRLs, since few lenses are optimized for CDAF. All native Micro Four Thirds lenses, and some Four Thirds lenses, are optimized for CDAF.

Comparison @ 14mm

There's a number of Micro Four Thirds lenses which include the 14mm focal length. So it's natural to compare their properties at this focal length. I've compared these:

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:

GH2 touch screen AF (superzoom example)

I've previously tested the touch screen AF of the GH2, using the 45mm macro lens.

Here's another example using the touch screen AF with the Lumix G HD 14-140mm superzoom lens. The lens was set to 100mm focal length.



As you can see, the response is still somewhat slow, but the actual focus action of the lens is faster than when using the Lumix Leica 45mm f/2.8 macro lens.

I'm using the A mode on the mode dial. Using the iA mode typically gives me the focus tracking mode, in which the response time from touching the screen until the focus changes is a bit shorter.

When using the shutter button to trigger focus, the focus is very responsive, just like in my study of the GH2 autofocus speed.

When recording videos, you can change the focus areas using the touch screen as well. The response and speed is similar to this example.

I have also made an analysis of the focus speed of the GH2 for a number of lenses, and compared with GH1 for some of them.

Index of lens related articles

Here is an index of lens related articles on this blog, sorted by lens:

Panasonic Lumix X 12-35mm f/2.8



Review

Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro



Review

A study of the bokeh at various apertures

Bokeh comparison with Lumix G HD 14-140mm and Lumix G 45-200mm, all at 45mm

Bokeh comparison with the Olympus Zuiko 50mm f/2 1:2 Macro

A study of the diffraction effects when using smaller apertures

A verification that the enlargement is actually 1:1

Example use of the touch screen AF with Panasonic GH2

A sharpness comparison with the Olympus Zuiko 50mm f/2 1:2 Macro at a long focus distance

A very simple sharpness comparison with the Olympus Zuiko 50mm f/2 1:2 Macro at a close focus distance

Autofocus speed

Olymus M.Zuiko Digital 45mm f/1.8



Review

Optical performance comparison with the Panasonic Leica 45mm f/2.8 macro

Panasonic Lumix G 20mm f/1.7 Pancake



Review

Autofocus speed comparison

Using a third party screw in 46mm metal hood, Leica Summicron type

Using a 46mm to 37mm step down ring as an alternative, low profile hood

An example video capture with the Panasonic Lumix GH1

Bokeh comparison with the Lumix G HD 14-140mm

Using the Lumix 20mm as a portrait lens

Distortion correction

Compared with the Lumix G 14mm f/2.5 pancake lens

A comparison with the Sigma 30mm f/1.4 lens on an APS-C camera. This is a lens that, in my opinion, does more or less the same job, and has around the same price point.

Panasonic Lumix G 14mm f/2.5 Pancake



Review

Compared with the Lumix G 20mm f/1.7 pancake lens

Comparison with the Lumix G 14-42mm and Lumix G HD 14-140mm zoom lenses at 14mm focal length

Autofocus speed comparison

Distortion correction

Measuring the field of view

Lumix G 100-300mm f/4-5.6



Review

Sharpness comparison with the Lumix G 45-200mm and the Lumix G HD 14-140mm

Lumix G 45-200mm f/4-5.6



Review

Bokeh comparison with Lumix G HD 14-140mm and Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro, all at 45mm

A bokeh comparison with the Nikkor 200mm f/4 AIS, not conclusive

Autofocus speed comparison

A look at the relation between the focus distance and field of view

An example video capture

Lumix G X PZ 45-175mm f/4-5.6



Review

Sharpness comparison with Lumix G 45-200mm

Lumix G HD 14-140mm f/4-5.8



Review

Autofocus speed comparison

Bokeh comparison with Lumix G 45-200mm and Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro, all at 45mm

Bokeh comparison with the Lumix 20mm f/1.7, both at 20mm

Example use of the touch screen AF using Panasonic GH2

Lumix G 8mm f/3.5 Fisheye



Review

Autofocus speed

Using the fisheye lens as a macro lens

Sigma 19mm f/2.8 EX DN



Autofocus speed comparison with the Lumix G 20mm f/1.7.

Sharpness comparison with the Lumix G 20mm f/1.7.

Sigma 30mm f/2.8 EX DN



Review

Samyang 7.5mm f/3.5 Fisheye



Review

Field of view comparison with the Lumix G 7-14mm f/4 wide angle zoom

Projection comparison with the Lumix G 8mm f/3.5 fisheye lens

Olympus Zuiko Digital 50mm f/2 1:2 Macro (Four Thirds lens)



Review

Manual focus with the Panasonic Lumix GH1

Bokeh comparison with the Panasonic Leica Lumix 45mm f/2.8 Macro

A simple sharpness comparison with the Panasonic Leica Lumix 45mm f/2.8 Macro

Using a cheap and simple macro soft box

Lumix G 7-14mm f/4 wide angle zoom lens



Short review

Field of view comparison with the Samyang 7.5mm f/3.5 fisheye lens

Firmware v1.3 for Lumix 14-140 and AF speed

In the beginning of October 2010, a new firmware version 1.3 became available for the Panasonic Lumix 14-140mm f/4-5.8 superzoom lens. The new version is said to give faster AF speed, as well as faster startup time.

I have previously tested the AF speed of the Lumix 14-140mm. My conclusion was that the AF speed was very fast, albeit with some hunting in the longer end of the zoom, at close to the minimum focus distance. So I wanted to see if the new version improved the focus speed.

Again I used the same setup, with a LEGO figure as object to be photographed. The LEGO figure was placed at a distance of 0.5 meters, which is the minimum focus distance for the lens. After turning on the camera, I pressed the shutter release button, and measured the time until focus was achieved. The lightning was dull, about 6 EV.

I used the Panasonic Lumix GH1. Here's the experiment using firmware version 1.2:



And using the firmware version 1.3:



The time until focus was 0.76 seconds with firmware version 1.2, and 0.68 seconds with the latest firmware version. This is hardly any significant difference, but there is still some improvement.

I was not able to reproduce the focus hunting at 140mm that I experienced in my first comparison. The first test was done using firmware 1.1, so I guess this was fixed already in the version 1.2.

Bokeh comparison @ 20mm

I have two lenses that can do 20mm, so I thought it would be interesting to compare their bokeh. Both the Panasonic Lumix 20mm f/1.7, and the Panasonic Lumix 14-140mm f/4-5.8 zoom comprise the 20mm focal length. Apart from this, they are of course very different. At f=20mm, the superzoom has a maximum aperture of f/4.4, which is quite a bit smaller than the f/1.7 that the fixed 20mm prime can do.

To compare the lenses, I have taken the same picture with various apertures. The centre region is in focus, and the focus distance is around 60cm, just above the minimum focus distance for the 14-140mm superzoom lens.

First the picture with the Lumix 20mm f/1.7 at maximum aperture. The picture is rescaled and sharpened a bit.

Second, the same image taken with the Lumix 14-140mm at 20mm f/4.4:

Click for larger images.

The make the comparison more sensible, I have looked at 100% crops from the image at various apertures with both lenses (click for larger image):

And here are 100% crops from another region of the image. It was a bit more windy in the second series, so the leaves were not always in the same spot.

Conclusion

It is not surprising that the bokeh for the 20mm prime lens is the best. For out of focus highlights, the bokeh is pretty even, but has hard edges. On the other hand, it is not entirely round, especially when stopping down. All in all, the bokeh is pleasant, and has no significant ringing. The superzoom bokeh is a bit "dirty".

You'll also note some differences in sharpness. Note, however, that a higher ISO value was used for the f/8 and f/11 images for the 20mm prime lens. So some lack of sharpness could be due to using a higher ISO. It can still be noted that the superzoom lens appears very sharp.

The 14-140mm also has more flare, which is due to it's more complicated construction. The 14-140mm lens has 17 lens elements in 13 groups, while the 20mm pancake only has 7 elements in 5 groups. Generally speaking, the less number of lens elements, the less problems with flare you're likely to see. Of course, many other factors also affect flare.