Diffraction is an optical effect which limits the total resolution of a camera — no matter how many megapixels the camera sensor has. It happens because light begins to disperse or “diffract” when passing through the small opening that is the lens aperture. The smaller the aperture the greater the diffraction.
Countering diffraction is the fact that most lenses are sharper at smaller apertures than they are wide open, although only to a point – it follows therefore that there is a cross-over point where diffraction becomes more impacting than reducing the aperture can counter. At this point the camera is said to have become diffraction limited. Knowing this limit can help maximise detail, and avoid an unnecessarily long exposure or high ISO speed.
The larger the sensor the camera has the smaller (in f terms) the aperture can be before diffraction sets in – given the relatively small m43 sensor in the G9 in theory diffraction will set in at a somewhat larger aperture than would be the case with an APSC or Full Frame camera.
Using maths (which I will not go into here) it is possible to calculate the aperture at which in theory diffraction sets in – for the G9 that aperture is around f/16.
So how does the theory work out in practice ?
Well – here is a test with the PL 12-60mm f/2.8-4.0 lens at 60mm.
Firstly a reference image.
and here are crops of images at apertures from f/4.0 to f/22.
Click on the image to see it large
Careful scrutiny does indeed show that the image does start to soften past f/11.0 and is noticeably softer at f/22 thus supporting the theory that on an m43 camera diffraction does set in at about f/16 and that the sharpest images (at least on this lens) are captured at about f/8.0.