It's about depth of field, i.e. getting that beautiful out of focus effect for backgrounds (bokeh) to isolate your subject. And also about megapixels. Shooting

It's about depth of field, i.e. getting that beautiful out of focus effect for backgrounds (bokeh) to isolate your subject. And also about megapixels. Shooting with a portrait lens on full frame e.g. 85mm at f1/4 at 2m from a subject I have about 4cm depth of field, with everything outside of that increasingly blurred. On a micro 4/3 the closest equivalent zoom would be using a 42mm lens, say at f1.4 which would have 9cm depth of field, equivalent to a full frame 85mm at f2.8. The advantage of mirrorless camera size then goes away because lenses with wide aperture are bigger and heavier, because of physics. I don't know what the advantage of medium format is at this point. I have the A7R III which has 42mp and a wide range of Sony and Canon lenses available. The quality is amazing, it's a relatively light, and relatively 'affordable' compared to medium format when you take into account body and high quality lenses.