This means they need a lot more light to get good photos; using a long telephoto lens … Here’s how to use a telephoto lens to put a background out-of-focus: The out-of-focus effect of f2.8 on a background is much greater with a 200mm lens then with a 50mm lens. A telephoto lens has a long reach—traditionally this means a focal length of 60mm or more—but it does not necessarily need to slide through a range of focal lengths. The telephoto lens is mainly used to put the background of an image out of focus and change the perspective to allow more depth. Telephoto lenses also require faster shutter speeds to get sharp exposures. To see just how versatile they are, here are 8 top ways you can use a telephoto lens. Effects of a Telephoto Lens on Your Photos. Telephoto lenses have a multitude of uses and can be a great tool in a photographer's arsenal. The telephoto lens on phones is a vital part of that blurred background, bokeh effect you see in so-called ‘portrait mode’ shots these days. Even with a tripod, if you use a telephoto lens with a shutter speed lower than about 1/200th of a second you risk having camera shake in your images. ; By contrast, a zoom lens … So if you … Some amateur photographers use the term “telephoto lens” as a synonym for “zoom lens.” In truth, these two lenses are not identical.