On the lenses, I have used 46mm to 28mm step down rings as hoods. They do a good job of keeping the front lens elements safe from accidents, in my opinion, while also keeping out some stray light. If you want to use them, you also need a 28mm front lens cap.
But how does the Lumix GM1 fare, in terms of image quality? Most appear to agree that the Lumix GH3 has a sensor from Sony, while the Lumix GM1 is generally believed to have the newest generation sensor from Panasonic. Apart from this, the sensors have quite similar general characteristics, like the same resolution (16MP), and the same base ISO 200.
To compare them, I have taken the same image with both cameras, using the Sigma 30mm f/2.8 DN lens at f/5.6, on a tripod, and using 2s self timer for the best stability.
I took these images at different ISO values:
|Lumix GM1||Lumix GH3|
Here are some 100% crops for comparison (click on the images for larger copies):
I had the same image settings in both cameras, still, it seems like the GM1 had a different approach to noise reduction at high ISO: It appears smooth out the colours a bit more, and loses some details. The GH3, on the other hand, retains a bit more detail, but also exhibits more noise.
To try to make a fair comparison despite these noise reduction differences, I developed all the images in Silkypix 4.1 with the same settings, and then made the same crop comparisons. Here they are:
In this last comparison, there appears to be slightly less noise and more details with the Lumix GM1 at high ISO.
At low ISO, the Lumix GH3 appears to be less sharp on pixel level. This is consistent with the common assumption that the GM1 has a weaker low pass (anti aliasing) filter, or lacks it completely. The GH3, on the other hand, being more optimized for video, has a stronger AA filter. A strong AA filter gives less sharpness at pixel level, but avoids the risk of moiré.
These differences could still be due to Silkypix treating the RAW files differently depending on what camera they came from, even if I set the same image processing parameters. But all in all, I think it is quite clear that the GM1 gives the best image quality at both high and low ISO.
Another thing to note is that the images from the GM1 have about 2% wider field of view, despite using the same lens at the same focus distance. So is the GM1 sensor larger? Probably, it is slightly larger. But 2% difference is just barely noticeable.
If you use a wide angle lens, though, 2% difference in field of view could actually make some difference, so this news could be of interest.
In a way, this difference in sensor size is already known, albeit not very widely: The Sony based sensor sitting in the Lumix GH3, Olympus E-M5, E-P5, E-PL5, E-PM2 is known to be slightly smaller, and gives you somewhat more narrow field of view compared with other cameras, given the same lens.
This picture illustrates the relative difference in sensor size:
The Lumix GM1 image quality appears to be state of the art. The sensor also appears to be slightly larger than that in the GH3.
Generally, People believe that the Lumix GX7 has the same sensor as the GM1, so you should expect similar results with that camera.