120

120 is equal to 5!, or 5 factorial, or 5 × 4 × 3 × 2 × 1.

÷ 5     × 6

The fun bit about it is that the film unrolls off its plastic core and winds itself around another identical plastic core. When the film is over, you open the camera and find that the curl of the film is keeping it wound.
But since we are real paranoid, there is one more fun activity: the last piece of film has a little paper tab with water activated glue on it. You wet it and then use it to seal the roll close.

Kodak at a certain point advertised as a feature the fact that the little paper tab was lemon flavoured, which tells you something about the disgusting habits of pro photographers.
Of course, one might wonder where does the first roll core come from. You are given one with the camera, they say. And what if you lose it ? I don't want to know.

There are many image formats that use 120 film. The most common are

• 4.5 x 6 (all sizes are in centimetres), first of the medium format formats, handy because it is more or less like 135 in image ratio. Many good cameras in this size, even one autofocus (Pentax makes it).
• 6 x 6 : the classic Hasselblad and Rolleiflex square format, loved by pros and wedding photographers.
• 6 x 7 : a big Pentax camera was made in this format, looks like a giant old Nikon.
• 6 x 9 : again, the 2:3 image ratio, getting really big. Some Fuji cameras in this size.
• 6 x 10, 6 x 12, 6 x 18: panoramic formats, very impressive on the light table, absolute hell to print and file. Only for the very obsessed.

120 film is paper backed and it has frame numbers (for 6x6) on the back. This was meant for very old cameras (this film format came out with the Kodak No.2 Brownie in 1901) that had no frame counter, and instead relied on a little window in the camera back that allowed you to see the numbers go by.
The paper backing was required to prevent fogging.

This format being very much in use (mostly by pros or advanced amateur), a lot of new emulsions come out in 120 also.

120's best buddy is 220 film. See also 620 film.

In Judaism, 120 considered an ideal age at which to die. This is generally because Moses is said to have died at this age. This concept is the root of the expression, "Ad me'ah v'esrim shanah" (Hebrew: until one-hundred and twenty years). It is a common blessing for longevity among Jews. There is an old age home in Israel called Ad Me'ah V'ersrim