What is a magnifier? An why i should use it when other cameras i don't use, feeling one more tool to use.

Why i want to use Hasselblad and not stick with RZ is because RZ is too heavy and it is not mechanical, i changed the battery many times and also sometimes i take out to shoot and find out the battery charge is gone, so disappointing, i can go with RB which will solve this problem but then it is also very heavy camera, i really love the handle of my 501CM, even the sound of its shutter is way tasty ad s..y, sticking with RZ is not a solution for Hasselblad using.