We look at buying a used EOS 5D in the November issue of What Digital Camera – out now. The MkII was quite an update from the original 5D – most noticeably the increase in resolution to 21MP from 12MP and full HD video.
That said, the EOS 5D is still an excellent piece of kit. As long as you know it’s limitations – its more suited to considered landscape photography rather than action and you can pick ‘well-loved’ examples up for around £699.
The biggest differences for me aren't actually the headline ones, but the sensor cleaning and Live View, and the better high ISO performance. The 5D is still a very capable camera, but the Mk II is just that much better.