Canon EOS 30D - Manual (Page 70)

70
The file number is like the frame number on a roll of film. It can start
counting in one of three different ways: [Continuous], [Auto reset], and
[Manual reset]. The images you take are automatically assigned a file
number from 0001 to 9999 and saved in a folder that can hold up to
9999 images. The folders will be automatically numbered from 100 to
999.
1
Select [File numbering].
Turn the <5> dial to select [c File
numbering], then press <0>.
2
Select the file numbering method.
Turn the <5> dial to select
[Continuous], [Auto reset], or
[Manual reset], then press <0>.
Even after you replace the CF card, the file numbering will continue in
sequence from the last image taken. (The folder number is also
retained.) Since this prevents having identical file numbers, it is
effective for managing images in the same folder with a personal
computer.
Note that if the replacement CF card contains images recorded
previously, the camera will compare the number of the folder where it
saved the last image and the highest numbered folder in the
replacement card. It will save new images to the folder having the
higher number, and the file number will follow the highest file number in
that folder.
3 File Numbering Methods
Continuous
XXX-0051
CF card -1
XXX-0052
CF card -2
File numbering after
changing the CF card
Next sequential file number