Have you ever wondered what's with the f/2.8 and 4/5.6 that people use in their photo descriptions, or what the difference between a 35mm f/1.4 and a 35mm f/1.8 lens is? Or for that matter, when people say they're "stopping down" for a shot, why does the f-number go up? In the second of our three-part series, we look at aperture and the impact small tweaks can have in your images…and yes, answering all these questions using as little jargon as possible.
So what exactly is aperture? The easiest way to
understand camera lens aperture is to liken it to pupils of your eyes, the holes through which light enters. And obviously, the wider they are, the more light they let in.
APERTURE MEASUREDThe complicated bit begins when you want to measure aperture numerically to make a better judgment of the right value for your shot. Aperture is measured using the f-stop scale, represented by the 'f/' followed by a number. Now here's the other important rule: the lower the number, the wider the aperture. This may seem confusing at first, but it's really quite straightforward-the f-stop scale goes something like this: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. Notice how they are all fractions? These represent division of the focal length of the lens by the diameter of the lens' hole. So the smaller the denominator , the bigger the hole, and more the light that reaches the sensor. As you move right on the scale, or "stop down", the aperture decreases to half its size and allows in 50 per cent less light. Modern cameras list apertures in between these numbers as well, to give you finer control over the settings, so between f/2.8 and f/4, you have 1/3 stops as well, by way of f/3.2 and f/3.5.
Clearly, the larger the aperture, the more light will fall, and the more exposed the photo will be. If you take photos at fixed ISO and shutter speed and vary the aperture, you'll notice two things as you move from a wider aperture to a smaller aperture. The first is that the images you make will be progressively darker due to the lens allowing in progressively lesser amount of light with each increase in f-number.
The second outcome is on depth of field (DoF), an effect that can be put to creative use in your photos. Put simply, the depth of field is the distance at which the subject will stay in focus in front of and behind the main point of focus. At a wide aperture, you will have images with a shallow depth of field and a blurry background. The wider the aperture (say f/1.8), the shallower the DoF, and narrower the aperture (f/22), the deeper the depth of field. Choosing to blur your background, also referred to as bokeh, can give your viewers a focus point without being distracted by objects in the background.
WHAT APERTURE TO USE WHEN?Put the effects of aperture into action. Although there are no rules to picking an aperture value, traditionally though, you should use low f-numbers, such as f/1.4, f/1.8 or f/2, for conditions where you want an extremely shallow DoF, or if you're shooting in low light. Great for well-lit wildlife and product photography, as well. Ramp it up a notch higher to f/2.8 to capture good facial detail in low light. If lighting is good, pick a value of f/4 or f/5.6 for people photography so that you're not risking body parts going out of focus with a shallow DoF. A mid range number such as f/8 or f/11 is typically where your camera shoots its sharpest image, so when neither a large nor a very small aperture is needed and the lighting is good, these are good apertures. Small apertures, such as f/16 and f/22, increase DoF, which means more elements of a picture, from the foreground to the background, are in sharp focus. This adds a sense of depth to pictures and is a must for landscape photos. But keep in mind that small apertures need bright lighting for proper exposure.
APERTURE WHILE BUYING LENSIf you've never shopped for a camera lens, be prepared for sticker shock when you see the price difference between an f/1.4 and an f/1.8 lens. Nowhere is this difference felt more than in telephoto/zoom lens, where a f/2.8 lens fetches a premium-we're talking about lakhs of rupees-over a lens that has a widest aperture of f/4. For the most part, if you're picking up a fixed focal length lens, an f/1.8 lens will meet all your needs. Most capable zoom lens start at f/3.5, though you'll want to see the maximum aperture listed at the longest end of the zoom to be able to tell what kind of low-light performance the lens can deliver when fully zoomed out.
