DE­COD­ING APER­TURE

IN OUR THREE-PART SE­RIES ON THE BA­SICS OF PHO­TOG­RA­PHY, WE TACK­LED ISO LAST MONTH. THIS TIME WE BRING YOU THE LOW­DOWN ON HOW APER­TURE CAN AF­FECT YOUR PIC­TURES. LEARN HOW TO USE THE F-NUM­BER TO GET THE RIGHT AMOUNT OF LIGHT IN THE PHO­TO­GRAPH.

Gadgets and Gizmos (India) - - DIGITALLIFE - BY TUSHAR KAN­WAR

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 MEA­SURED

The 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.

APER­TURE, EX­PO­SURE, DoF

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 LENS

If 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.

The cam­era shoots the sharpest at a mid-range like f11, but re­quires good lighting.

Neil Arm­strong2/flickr

Land­scape pho­tos re­quire ev­ery­thing to be in fo­cus. So a nar­row aper­ture, like f22,works well.

An aper­ture of f4 al­lows nei­ther too shal­low nor too deep a depth of field.

With a wide aper­ture of f1.8, you can blur out the back­ground.

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