This type of lens has great magnification compared to a normal lens. This range starts at approximately 300mm. This would magnify the image by 6 times compared to a 50mm normal lens on a 35mm full-frame or digital full-frame sensor. If it is used with a smaller sensor, the focal length is magnified by a factor of typically 1.5 times, that would make it equivalent to 450mm on 35mm full-frame. These lenses have a much longer minimum focus area and can become quite heavy. This type of lens is used for nature, sports and surveillance. When using one of these lenses, your shutter speed should be at least the same or faster than the focal length. Even using cameras with optical image stabilization, you still should be on a tripod or unipod. It is very hard to hold this type lens and get sharp images. You are magnifying the motion of your hands. This type lens can be 250mm, 300mm, 400mm, 600mm, 800mm and 1000mm and in some cases even higher.