Medium format refers to roll-film cameras whose image formats are larger than 35mm film (often significantly so). Top quality medium-format SLRs like the Hasselblad or TLRs like the Rolleiflex were the workhorses of professional photography until digital photography displaced them. The term medium format almost always implies 120 film, although 220 (double the length of 120) and 620 (essentially 120 on a skinnier spool) would also qualify. In contrast, large format implies a camera designed for sheet film of 4×5" or larger. The 4×6.5cm vest pocket format of some cameras for 127 film defines the smallest medium format, while due to the actual state of progress of medium format sensor engineering in 2013 digital imaging sensors sized 49.1×36.8mm (Kodak 50 megapixel) and 53.8×40.3mm (Dalsa 60 megapixel) are also reckognized as almost the effective frame size 41,5×56mm of the second smallest medium format 4.5×6cm on film.