The number of shutter actuations on older Canon cameras is encoded in the 'Image Number’. On my 10D, it shows 2929222 approaching 3 million shots which is clearly wrong. One EXIF data tool reports the number as 292-9222. That makes more sense – the last image was IMG_9222.JPG. I then realised that the first 3 digits are in fact the folder number on the memory card.
Under DCIM there are two folders at present: 291CANON and 292CANON. The folders each hold 100 files so the first 3 digits increment once every 100 images to reflect the new folder number while the last 4 digits increase to 9999 then rollover to 0. A twist is that looking at one of the early images I took with this camera is that the folder numbers start at 100 rather than 0. Thus to convert the image number to the number of shots taken we need to do the following:
- Split the image number into two parts: the last 4 digits (call this file number) and the first three folder number. We then need to do a bit of arithmetic.
- Shutter Count = (folder number-100)*100 + modulo 100 file number. Modulo 100 may sound frightening, but in reality it means just take the two right hand digits.
So for my 10D
Shutter Count = (292-100)*100 +22 = 19200 +22 = 19222 shutter operations
Newer cameras store more images in each folder, so the mathematics change.