The focusing aid as it works perfectly, but you have to remember one thing. Due to the small viewfinder an Corp Kammera a focusing on aperture 1.4 -2.8 is just not easy. In Still Life certainly doable with a little patience, but once something is moving, virtually impossible. Since you have significant easier time at a Kammera full frame. What indeed is no wonder the viewfinder is indeed much bigger. Which of course has a positive effect on the application areas of a focusing disk.
++ From Aperture 2.8, the focus point can be adjusted quite well.
Another advantage is this focusing screen but still. And that is not to be underestimated. Away from the circle for focussing it is matter created when the transparent as possible slices of the manufacturer.
++ This can be seen directly in the viewfinder, what impact has the selected aperture on the final image!
Whether it has an impact on the exposure, I can not say. But I'm assuming. Just outside the circle, it can certainly be differences. But I have not really seen in my pictures. But I use them too much too rarely.
