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.
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.