How do the pros get such sharp photos? It’s more than just shooting at a high enough shutter speed to avoid camera shake. Every lens, ever made, at any price will take sharper pictures at some aperture settings than others. So how do you know where your lens shoots at its sharpest? Generally speaking, your lens is the sharpest at two full stops smaller than wide open. So if you’re shooting with the lens that came with the camera and it’s aperture range is from f3.5/f5.6 to f16, then the best aperture for sharpness is going to be f8 or f11.
Now before we go any further let’s look at the funny way I indicated the wide-open f-stops. In the example above I said the range started at f3.5/f5.6. This dual f-stop number shows that the camera manufacturer saved money and weight by going to a variable f-stop when shooting wide open. In other words when the lens is zoomed out wide the aperture is going to be f3.5 but then it’s zoomed in and is at its longest setting it will be opening to only f5.6. For most amateurs, having a slight change in the f-stop reading while zooming in and out doesn’t matter. But in critical situations, like wedding photography, it’s best to be using a fixed f-stop lens to maintain the same exposure regardless of the zoom. That’s one of the reasons wedding photographers buy such fast, heavy and expensive lenses. A 17mm to 55mm f2.8 or a 70mm to 210mm f2.8 are heavy, fast, expensive and do not change their exposure settings (by changing the aperture) during zooming.
The second reason pros buy fast lenses with a fixed rather than a variable aperture, is a fast lens opened up wide (f2.8 or lower) yields a photo with very narrow depth of field. Shooting like this isolates the subject from the out-of-focus background. Here’s a shot of a fiddlehead which is in focus and set against a background that’s out of focus. It’s too bad I don’t shoot weddings so we’ll have to settle for the fern but if you go to any great wedding photographer’s website you’ll see examples of the single-focus, narrow depth of field shot of the bride.