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