Most Canon EF midrange and better lenses have distance scales - clear rectangular plastic windows set into the lens barrel. A series of numbers can be seen through this window indicating the distance, in both metres and feet, from the lens to the point in focus. Inexpensive consumer lenses generally do not have distance scales.

Canon EF prime lenses also have simple depth of field scales marked on the barrel below the window. These marks indicate the acceptable depth of field distances from the current focus distance, usually for a small number of apertures - f/11 and f/22, say, or f/5.6, f/11 and f/16. Canon EF zoom lenses, however, do not have any depth of field scales because of the complexity of indicating depth of field over varying focal lengths.

You’ll notice that there is usually a red dot on the distance scale window as well. This is used for determining the focus distance when using infrared film with an infrared filter. Since infrared energy focusses at a different point from visible light this dot is a useful aid. However, if you’re using infrared film with an ordinary red filter or no filter at all then you may not need to adjust focus using this dot, since much of your image is going to be visible light anyway. For more information please consult my Infrared Myths document.