The Olympus 75mm f/1.8 M.Zuiko is a mid-telephoto lens for cameras Micro 4/3 sensor and mount. This lens will perform well on any Micro 4/3 camera such as Panasonic GH series but has special lens mapping and improved image performance when used with an Olympus PEN or OM-D camera.
LensFinder has scoured the internet for an industry expert point of view and round up of info on this lens.
To start you should consider what it means to shoot with a telephoto lens. 75mm focal length on a Micro 4/3 sensor has the field of view of a 150mm on a full frame 24x36mm sensor/film such as the Canon 5D or Sony A7/A9 series cameras. The 75mm f/1.8 is a telephoto and this means you will have to back up farther away from your subject that you may be anticipating. The working distance from you subject is often more than people appreciate and likely the number one reason you see this lens for sale by shooters on Lensfinder.com more than you would think.
BorrowLenses.com has a really nice article that explains telephoto photography in depth.