Weird, I was sure I read about the issue and it boiled down to the consensus that it doesn't make sense it's equipped with a 2.8 lens albeit hardly ever opening up to it (to keep things sharper)..
Thanks for posting the Mju II graphic, it's kind of the reverse of the Trip 35 which tends to stop down the lens as much as possible to keep depth of field
A gif says a thousand words innit