>>3132760>Exposition is given per unit area
... Do you mean exposure?>The EV value is still the same regardless of the aperture
Yes, this is true. But that's not what we're talking about.
So, you've got the normal triangle of exposure variables. Shutter, Aperture, ISO. If you adjust one, you have to adjust one of the others (or change your actual light in the scene) to compensate.
The larger sensor means that a given aperture and field of view is going to give you shallower depth of field. So if you DON'T want shallower depth of field, you have to stop down your lens.
So shooting 35mm, 1/200th, ISO 100, f/2.8 on a crop camera ~=
Shooting 50mm, 1/100th, ISO 100, f/4 on full frame ~=
Shooting 80mm, 1/50th, ISO 100, f/5.6 on 645 medium format.
You could just shoot FF at 1/200th f/2.8 and the MF at 1/200th f/2.8, but your depth of field would be shallower on FF and way shallower on MF.
Going from crop to FF, you also have this option: 1/200th, ISO 200, f/4. That would give you the same DOF and same shutter speed (i.e., same level of motion blur), and it would even give you the same level of noise because FF sensors have less noise than crop sensors.
This does NOT hold true for medium format sensors, though. The ISO characteristics of medium format are more like crop than like full frame, usually, and only the best and most modern MF cameras can match FF for ISO noise.
So, if you want to hold these variables constant:
* Amount of noise in the photo
* Depth of Field
* Motion blur
then for medium format, you have to increase the light in the scene.