All 35mm lenses have an image circle that covers the entire 35mm film area. The sensor in the 20D is APS size, smaller than 35mm. This means that the 20D is only using the center of the lens, it is cropping off the edges. This gives you a smaller angle of view but everything else stays the same. It's as if you cropped a picture in PhotoShop.Originally Posted by siberia1997
The eyepiece of the 20D will show you what you will get (it might be 95% like most cameras). SLRs do not have an LCD preview like consumer P&S cameras. The image on the LCD after your shot is 100%.