Canon employs a simple model numbering system on their EOS range:
- Single digits such as 1, 3, 5 etc indicate models aimed at professional or semi-professional (pro-consumer) use, with the 1 being top-level professional gear.
- Two digits such as 10, 20, 30, 40 etc indicate models aimed at enthusiastic amateurs and semi-professionals.
- Three digits such as 300, 350, 400 etc indicate models aimed at budget or entry-level buyers.
Usually the higher the number in each category the later the release--with the exception of the single digit professional range!
When the digital technology hit us, all Canon did was add a D to the end of the model number to indicate it is a digital SLR rather than a 35 mm film SLR. Eg; EOS 30 (film) and EOS 30D (digital). Further more, Canon made sure all their EOS models were fully compatible with their extensive range of EF series lenses, right back to the 80's. Although some newer lens features such as distance data for flashlight control algorithms may not be read by older EOS bodies, all earlier EF lenses will function fully on newer EOS bodies.