Un­sure how much of your sub­ject is in fo­cus? An app on your phone might be the an­swer...

Go! Camp & Drive - - Contents - Text and pho­tos Vil­liers Steyn

If you’ve read Dig­i­tal Pho­tog­ra­phy for Dum­mies or spent some time watch­ing YouTube tu­to­ri­als, you’ll know the ben­e­fit of chang­ing your cam­era’s f-stop when pho­tograph­ing wildlife. This is done in Aper­ture Pri­or­ity (A/Av), and the prin­ci­ple is sim­ple: if you de­crease the f-stop, less is in fo­cus, and if you in­crease it, more is in fo­cus. In other words, you’ll likely use a small f-stop (f/2.8 – f/5.6) when you want to blur the back­ground when tak­ing a por­trait photo of a lion and a larger f-stop (f/10 or greater) will work well when pho­tograph­ing a herd of ze­bra graz­ing on an open plain. The ques­tion is: have you ever given any thought to what the ac­tual depth of field is, in cen­time­tres, when you take pho­tos? And did you know that the dis­tance be­tween you and the an­i­mal greatly in­flu­ences this value?

1An ex­po­nen­tial drop

Let’s look at an ex­am­ple: You’re in the Kruger Na­tional Park and a leop­ard stands 30 me­tres away from you and you’re pho­tograph­ing it with a Canon 7D MkII and a 100-400 mm lens at f/5.6 for max­i­mum back­ground blur. What is the depth of field? 119 cm – more than enough to en­sure all of it is in fo­cus when you’re pho­tograph­ing it side-on. It’s your lucky day and it walks half­way closer to you. What’s the depth of field now? Half of 1.19 m? No! It’s only 29.43 cm. And if you were in the Sabi Sands and the leop­ard comes to stand five me­tres from you? Be­lieve it or not, but the depth of field drops to 3,09 cm! The depth of field there­fore drops ex­po­nen­tially as the dis­tance de­creases, and thus, at this close range, even if you’ve fo­cussed on one of the an­i­mal’s eyes, the other one will most likely be out of fo­cus if you don’t in­crease the f-stop slightly.

2Su­per-smart app

How on Earth did you cal­cu­late those val­ues, I hear you ask. Why, with the Sim­ple DoF Cal­cu­la­tor* app by Den­nis van den Berg (US$1.99) on my iPhone of course. You sim­ply se­lect your cam­era model, f-stop, fo­cal length and dis­tance to your sub­ject, and the app au­to­mat­i­cally cal­cu­lates the depth of field for you. If you don’t find your cam­era model in the list at the top, sim­ply click the re­fresh but­ton at the top right cor­ner of the screen. I’ve made a point of spend­ing as much time as pos­si­ble play­ing around with dif­fer­ent com­bi­na­tions of lenses and f-stops, learn­ing what the depth of field would be over spe­cific dis­tances. That way I train my­self to in­stinc­tively choose the right f-stops in the field. *As far as I know, Sim­ple DoF Cal­cu­la­tor is not avail­able in the Google Play store, but there’s a host of sim­i­lar apps that An­droid users can down­load. Sim­ply do a search for “DOF cal­cu­la­tor”. Im­prove your wildlife pho­tog­ra­phy skills by down­load­ing Vil­liers’s wildlife pho­tog­ra­phy app, Learn by Ex­am­ple – Wildlife Pho­tog­ra­phy, in the App Store or Google Play Store and fol­low his ad­ven­tures on In­sta­gram: @vil­lierssteyn

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