To test this, I took the same image using the Lumix G 20mm f/1.7 and Lumix X PZ 14-42mm f/3.5-5.6 @ 20mm. Both lenses were used on the GH3 camera, at f/5.6, with ISO ranging from 200 to 12800.
|Lumix G 20mm f/1.7 pancake||Lumix X PZ 14-42mm @ 20mm|
To investigate the banding problem, I have made 100% crops from the images at the ISO values 200-12800. Click to enlarge the image:
Based on these images, it is not easy to find any systematic difference between the Lumix G 20mm and Lumix X PZ 14-42mm lenses.
According to other people's findings, this problem can be seen in the shadows at high ISO. So, here are two more crops at ISO 12800, f/5.6, 1/80s:
Perhaps one can say that there is some more systematic banding with the 20mm lens, but it is certainly very hard to see. I don't think there are any significant stripes in the left image.
I tried a second shoot at ISO 6400, this time with the Lumix G 14-42mm f/3.5-5.6 as the alternative lens. The exposure parameters are: 1/60s, f/5.6.
|Lumix G 20mm f/1.7 pancake||Lumix G 14-42mm @ 20mm|
And a comparison at 100%:
Again, I don't see any problems with banding when using the Lumix G 20mm f/1.7 lens.
Finally, here is a comparison with the Sigma 19mm f/2.8 EX DN lens, with a similar focal length:
|Lumix G 20mm f/1.7||Sigma 19mm f/2.8 EX DN|
|@ ISO 6400, f/5.6, 1/6s||@ ISO 6400, f/5.6, 1/6s|
And here are 100% crops at both ISO 6400 and 12800:
The images are a bit dark, so I tried to use the curves tool to bring out more details:
In terms of banding or stripes, I am not able to see any significant difference between the two lenses. I can't see any significant banding when using the Lumix G 20mm f/1.7 lens.
Here is an example video using the Lumix G 20mm lens on the GH3 at ISO 3200. I don't see any banding issues here:
Source of the problem
There has been some discussion about why banding problems were experienced with the Lumix G 20mm f/1.7 lens exclusively. Some have suggested it may be due to the focus construction of the lens. It is one of the very few Micro Four Thirds lenses which has a traditional focus mechanism, in which all the lenses move back and forth. This takes a stronger motor, and is slower and more noisy than internal focusing. The lens also has a large spiral spring in the focus assembly, and a lot of people have suggested that this might be the source of the problem.
Since the banding issue has been seen on the Olympus OM-D EM-5 and Panasonic GH3, some think this is a sign that their sensors are related, and share vital parts.
Also, it should be noted that if you use the electronic shutter option with the Panasonic GH3 in combination with fluorescent light (indoor), you may get banding with certain shutter speeds. There is an easy to understand explanation for this: Fluorescent light flickers with a frequency of 100Hz or 120Hz (depending on the country), and the electronic shutter reads out the imaging sensor sequentially during about 1/10s. Hence, a shutter speed faster than these shutter speed will give you significant banding. Read more about this here.
In my tests, I have not been able to find any significant negative effects due to banding with the Lumix G 20mm f/1.7 lens. My conclusion is that it is safe to use this lens, also at high ISO.
On the other hand, I have seen people posting example images where the banding problem can be seen, so I don't doubt that it can be a problem.
Another conclusion is that the ISO 12800 image quality of the GH3 is quite good. There is a lot of noise, of course, but still an amazing level of details. For web use, the images are usable.