The film stock is identical; only the spools differ. The 620 spool has a thinner axle, the end caps have a smaller diameter by about 2mm, and the overall length of the entire spool is about 2mm shorter.
120 film is still readily available but 620 film is very hard to find. There are two options:
- Buy some empty 620 spools, and respool the 120 film in a darkroom
- Modify the 120 spool of each new film by filing it down
I find roll film quite frustrating to work with in a darkroom and I didn’t fancy respooling it unless there was no other choice. So I decided to have a go at butchering a roll of 120. Even if it went wrong, I’d only have ruined £4 of film.
With the film still on the roll as new, I filed down the fatness of the end caps and then filed down their diameter. Fortunately I had one empty 620 spool to use as a template for my hack. It took only about ten minutes, but obviously filing away plastic left a lot of dust, so I had to make sure the film was extremely clean before putting it in the camera. I brushed it, and sprayed it with a can of compressed air.
The film now fits nicely into the Brownie, and I look forward to shooting with it. 🙂