Mostly for @Tamas_Papp:
As an example of low-light performance of the 12-35 mm: The empty street in Florence (pre-dawn) was shot at f/3.5 and 1/15 s at 15 mm and 1250 ISO. With both IBIS and lens stabilization, I think the image is acceptably sharp. BTW I have my own presets for denoising that I mention here:
Denoising in a PlayRaw
With the default denoising, I find that some details can look “blotchy” especially with low exposure.
Also, FYI I’ve just learned of an issue called “focus shift” that occurs with many lenses as you stop them down, due to aberration effects I think. Focus is with the aperture wide-open, and exposure is stopped down where the focus point shifts. Focus shift impacts the 50mm f/1.7.
The work-around for the G9 is to a) set constant preview (menu “c-spanner wrench” > i Monitor/Display> Constant Preview) and b) set manual exposure and use area autofocus. This forces the camera to stop down the lens for focusing. For the 25 mm f/1.7, this is best for focus at f/2.8 and f/4, when the subject is close. Also, FYI I use back-button focus, with AFS for still subjects.
Focus shift video
Panasonic 25mm f/1.7 mm Review
Edit: I just found another view of this issue on this lens by photographer Matti Sulanto who has made many YT videos on the G9 (but not lately):
Lumix 25mm F1.7 Focus SHIFT –Is it real or not?
Basically he agrees it’s a minor issue at longer focusing distance at f/4, but still thinks it is a very good lens.