A Real Estate Lens is a wide lens. On a full-frame digital SLR or 35mm film, a wide angle lens is generally considered anything with a focal length of 35mm or less. On a cropped DSLR, most people  aren't impressed by a wide-angle effect until you get down to 24mm. Wide angle camera lenses start to get expensive at 20mm ($500) and wider. So good compromises these days are are probably a fixed 24 ($250) or a high-quality 16-35 zoom ($1500). See the Fast Camera Lens at a Glance page for an idea of what lenses are available.

Digital Crop Factor:  Placing a 10-20mm lens on a digital body with a smaller sensor size produces a picture that is the same as the picture taken by 35mm frame body with a 15-30mm lens. This is known as the “digital multiplication factor”, or sometimes called the “Field Of View Crop Factor”. It is the size of the digital sensor, which decides the effective 35mm equivalent focal length of the lens. Various brand digital cameras have different multiplication factors. (Nikon is 1.5, Canon is 1.6 and the Canon 30D is 1.3) These factors are an advantage to photographers taking telephoto shots, but a disadvantage when shooting wide-angle photos with a digital SLR. It could also be a waste of an expensive lens that will only be using the center of the lens.