comments:
It's for ease of alignment. There are basically three different alignment systems I've seen: 6 screws, which will hold firmly, but are harder to align 3 screws at the back and a rubber O-ring at the front to act as a pivot, which will hold somewhat firmly, but can be harder to align because loosening any one screw without simultaneously tightening another can cause the finder to slip 2 screws at the back with a spring pin to apply constant pressure, and rubber O-ring at the front (the design of MK127's finder). This the easiest to align since you only have to articulate two screws, with the front O-ring and the spring pin acting as helping hands, but it also means it's less likely to stay in alignment. What I ended up doing with mine is replacing the internal spring with a stronger one. It wasn't a perfect solution but it helped. The ideal spring would be 0.8mm - 0.9mm wire, 12mm length, 5mm O.D, and only a handful of turns per cm (fewer turns = stronger spring). Hard to find that though. The one I linked to is the best I could find off the shelf. There is a 0.8mm wire spring that's 15mm long and 5mm O.D. but it has more turns per cm, and thus the spring force is no better than the 0.6mm wire one.