Upgrade 20D to a 5D?

Not a fullframe lens, but a fullframe camera, which means it doesn't have a crop-factor like your 10D. The 17-40L on the wide end on your 10D doesn't actually give you 17mm, but 17mm x 1.6, which is around 28mm. On 5D, 17mm is 17mm.

should of reread my post I did mean camera not lens, so I take it all lens are 1.6 x on a 10d and 20d but not the 5d and 1d.

1d is 1.3x, but you are correct about the rest.

Kristian wrote in post #4080143
Not a fullframe lens, but a fullframe camera, which means it doesn't have a crop-factor like your 10D. The 17-40L on the wide end on your 10D doesn't actually give you 17mm, but 17mm x 1.6, which is around 28mm. On 5D, 17mm is 17mm.

The focal length doesn't change. It's still 17 mm. The angle of view changes because of the smaller sensor. AoV of a 17 mm on a full frame is about 93 deg.; on an APS-C, it's about 67 deg. So you're seing less on the crop camera.

[Sorry for the duplicate post. Please delete this one.]

Yes, a 5D is a full frame camera, but you base that on its sensor, not on whatever lens is on it. Crop bodies like the 20D and 30D use the smaller APS-C sensors, and can use the same lenses as a 5D, but the field captured by the lens is cropped down. Here's an article that explains it all and in doing so compares the 5D to the 20D.

http://photo.net/equip​ment/canon/fullframe/