This article is a continuation from the "Mid-roll Change with a Canon Elph Jr." In that article we were able to get the Canon Elph Jr. to mid-roll change, even though it only supported mid-roll rewind. Unfortunately, the Elph Jr. is fooled into thinking the re-loaded film cartridge is brand new and winds the film to the first frame.
After playing with a half-exposed Elph Jr. film cartridge, here is a neat trick I learnt: the Canon IX can load a partially-exposed Elph Jr. cartidge to the right frame automatically.
By turning the film cartridge visual indicator to partially-exposed, I was able to load the partially exposed roll of film in my Canon IX SLR camera. (Remember to turn the film cartridge clock-wise, following the arrow.) The Canon IX camera automatically spooled the film to the right frame.
Note that the above procedure is not recommended by the camera manufacturer. Doing so may void your warranty and damage your camera equipment. I can not be held responsible for your actions.
Now I am able to load different film speed in my Elph Jr. and Canon IX without worrying about losing unexposed frames.