Вопрос о пленках

В частности вопрос о типах пленок, не буду перечислять все,но чем отличается тип 120 от 620 ????

The 620 format was introduced by Kodak in 1931 as an intended alternative to 120. Although mostly used by Kodak cameras, it became very popular. The 620 format is essentially the same film on a thinner and narrower all-metal spool (the 120 spool core was made of wood at that time) :

120 2.466" width, 0.990" flange, 0.468" core
620 2.468" width, 0.905" flange, 0.280" core

Hence the 620 is sometime referred as "small hole" 6×6 or 6×9 as opposed to 120 "large hole". The 620 format was discontinued by Kodak in 1995, but it is possible to rewind 120 film onto a 620 spool in the darkroom for use in 620 cameras. According to Kodak, the narrower metal spool allowed building smaller cameras. Nonetheless the 120 format cast-metal bodied Voigtländer Perkeo remains smaller than any 620 format camera.