Let me tell you a story. In the beginning there were the D30 and D60, which were 3 and 6 megapixels respectively. Simple.

But then they moved the D to the end and released the 1D, 10D and 300D (would have made sense to call that last one the 100D, but whatever). The number of digits now meant the market the camera was aimed at, 1 digit was a professional level camera, two digits for advanced amateurs, three digits for beginners / casual shooters.

Successive models in the two digit series got a +10 increment whereas successive models in the three digit series got a +50 increment. Professionals are rarely swayed by impressive sounding numbers so they just got a mark II mark III etc. progression.

The trend remained until Canon decided to make a mid level full frame DSLR which they called the 5D. Kind of halfway between one and two digits. Then a little later they announced the 1000D, generating a fourth line of four digit cameras.

All was relatively fine, the shoe-in 5D got a markII, there were always features which distinguished the lines even as megapixels and AF improved:

• 1D[s] weather sealing, 100% coverage viewfinders, vast numbers of AF points, built in grip, totally different control system, high number of megapixels

• 5D full frame, somewhat underpowered AF

• xxD 1.6 crop, metal body, pop-up flash

• xxxD plastic body, no LCD screen on top, SD card slot

• xxxxD entry level, priced agressively

Then came the 7D, which didn't really fit anywhere, so they shoe-horned it in next to the 5D, with which it has almost nothing in common, and the 60D which has gone plastic body and moved closer to the xxxD (should have been a 600D IMO), rumours of a 2000D, 3D so who knows what Canon are going to do next but they're running out of numbers in the xxD line!

Other Canon accessories are sensibly named, the EF 50/f.4 USM is a 50mm EF mount lens with max aperture 1.4 and ultrasonic motor. The 580EX flash is a flash with guide number 58. But camera bodies? The higher number is better unless it's less than 10 in which case the lower number is better, unless it's more than 100 in which case the higher number is better again, unless of course it's more than 1000.

These days it's better to look at the price and specification than to try and decode it!