Medium format refers to the size of your roll of film (or if you’re talking digital, it’s the size of the camera sensor). It really just means that you are shooting on a bigger piece of film than you do with a 35mm camera. The increased size of medium format film means a much larger negative. This will give you finer details and less grain.
Choosing your Right Medium Format Camera
Twin Lens Reflex (TLRS)
TLRs use two objective lens of the same focal length. The photographic objective lens is the one that is used to take the picture. The other lens, called the view lens, is connected to the viewfinder. Most TLRs are fixed focal length, and the more expensive models may incorporate a rudimentary room function. Most TLRs use a leaf shutter system, resulting in high speeds, quiet operation and low shutter vibration. There are also close-up, wide angle and telephoto adapters for TLRs.
Some popular TLRS cameras are: Yashica MAT-124G, Rolleiflex 2.8F, Minolta Autocord and Mamiya C330
Rangefinder cameras are medium format cameras with a range finder. This negates the waistline, viewing that most TLRs carry. They are also much smaller than TLRs, and allow for easier point and shoot photographs. They tend to have limited focusing ranges, and do not have lenses larger than 180mm or 200mm. Rangefinders are quieter and easier to focus in dim light. They are mostly fixed lens models, but higher range models also provide for interchangeability.
Some popular rangefinder cameras are: Fujica G690, Mamiya 6/7, Bronica RF645, Norita 66 and Pentax 67