A couple of months ago I bought a third-party zoom lens* cheap (28-70 made by Vitacon) with the knowledge that the AF wasn't working and that it would have to be used as a manual lens. Ok, fine. When I looked closer, I discovered that one of the CPU pins was missing, so I got my soldering iron out and put in a replacement. Ok, so now my F4 recognises it as a lens with a CPU (and can therefore be used in P or S modes), but the AF doesn't work. Not a problem, it could always be used as a manual lens at a pinch. Fast-forward to a couple of days ago when I got an F90x. Bizarrely, the lens works as an AF lens for this camera. I am slightly surprised by this, and didn't realise that the CPU communication would be different... is it just because the lens is from a cheap third-party, or is my F4 faulty in some way? (incidentally other Nikon AF lenses work perfectly with both cameras) Just odd, that's all * I was going to use it as a donor for the lens mount.