I am looking for any experiences comparing the quality of the lens on the Sony RX100 Mark 4 and the Mark 7. The reason for my question is that I own the RX100 Mark 4 and have been very satisfied with the quality of the lens, fairly sharp right to the edges/corners at f4 and f5.6. I recently purchased the Mark 7 from B&H and did a quick test comparing my copy of each camera. In the 24-70 range my copy of the Mark 7 had significant softening at the edges/corners at the same apertures shooting the same scene with the same settings on both cameras. While the test was done handheld, at 200 mm the Mark 7 was very sharp so I don't think there is a problem with image stabilization (plus shutter speed was 1/1600). The difference in lens quality was enough that I decided to return the Mark 7.
My question: did I get a bad copy or is this due to lens design? Trying to decide if I should buy another Mark 7 locally and test again as I would like the extra zoom range and don't need the wider aperture offered by the Mark 7.