https://www.techradar.com/news/best-micro-four-thirds-lenses

Most camera manufacturers these days seem to think that ‘full-frame’ is the way to go for optimum quality and versatility. However, anybody who’s spent time walking about with a clunky full-fat DSLR and 24-70mm f/2.8 lens hanging around their neck will know that this kind of camera outfit can really weigh you down. MFT (Micro Four Thirds) mirrorless system cameras and their relatively small, lightweight lenses let you literally take a load off.

At the heart of the MFT system is a comparatively small image sensor that has a 2.0x crop factor, compared with full-frame cameras. When it comes to shrinking the physical size of lenses, the advantages are two-fold. Firstly, the image circle produced by the lens only needs to be a fraction of the size of a full-frame lens, so the optical elements can be made with a relatively small diameter. Secondly, the actual focal length for any given type of lens is halved. For example, a 35-150mm telephoto zoom would give you the same ‘effective’ range as using a 70-300mm lens on a full-frame outfit. Again, the physical construction of the MFT format lens will be smaller and lighter.