Blurred vision…

To blur or not to blur. That is the question.

In this article, I’ll tell you how to control depth of field (or DOF) and try to show you when you don’t want it, when you do want it and what to do when it all goes horribly wrong!

How to control it

Depth of field is controlled by four variables:

• Focal length of the lens. The longer the focal length, the lower the depth of field.

• Aperture setting (ie f-stop). The wider the aperture (ie the lower the depth of field.

• Distance to the subject. The shorter the distance to the subject, the lower the depth of field.

• Distance to the background. The further away it is, the lower the depth of field.

All these variables are in your control to some extent, but it depends on the situation.

If you have only one lens with you, for instance, and it’s not a zoom, then you can’t do much about that.

Equally, if you’re in a fixed position such as a hide (or blind), you might not be able to change the distances involved (except by waiting for your subject to change position).

The picture of the leopard’s face below is a good example of this.

The animal was only three yards away from my jeep, and I was using my 800mm lens, so I had no chance of getting decent depth of field without narrowing the aperture.

However, it was after sunset, and it was getting pretty dark.

I’d already reduced my shutter speed to 1/250 of a second, but the ISO was still way up at 3200, so I thought I’d better shoot wide open.

I thought I could get away with it, but, unfortunately, the leopard’s nose is just a little blurred. Too bad…

In the case of the picture of the European bee-eater above, everything worked in favour of narrow depth of field:

• Focal length of the lens: 800mm

• Aperture setting (ie f-stop): f/5.6

• Distance to the subject: ~25 feet (8 metres)

• Distance to the background: ~100 yards (90 metres)

However, there will be other occasions when there are trade-offs involved.

For instance, if you want greater depth of field, but the light levels are very low and you want to minimise noise by reducing the ISO, then you’ll have to decide which is more important.

If you have plenty of time, then you can experiment and take a number of shots using different combinations of settings, but time is a luxury that wildlife photographers don’t often have!

As a general rule of thumb, I’d shoot wide open, but it’s worth looking out for those occasions when you positively want greater depth of field.

The other problem, of course, is how to find out what the depth of field is going to be.

There are three ways of doing this:

• Use the depth of field preview button on your camera (if there is one). This has the advantage of being something you can do before you take the shot, but the downside is that it will usually darken the image in the viewfinder. That’s because the DOF preview button changes the size of the aperture to the setting you’ve selected for the shot. If that’s not the maximum aperture, then it will become smaller, which means less light is able to enter the camera.

• Take one or two test shots to see what happens. The disadvantage of this is obviously that it’s a ‘trial and error’ approach that almost always guarantees a few mistakes. However, it at least gives you a proper yardstick by which to judge the depth of field. Are the cheetah cubs both in focus? Well, all you have to do is look on the back of your camera.

• Use an app such as SetMyCamera. This is not something you want to do all the time, but it’s very useful in setting yourself a few rules of thumb. If you have one or two ‘go to’ lenses (like I do with my 800mm and 80-400mm), then you can simply dial in the appropriate data (including the make of camera, focal length and one or two sample distances) and find out what the precise depth of field is for a given distance from the subject. And it’s often not as much as you’d think: the depth of field for my 800mm lens at 10 metres is only 5 centimetres!

Given the usefulness of long lenses in wildlife photography, it’s important to know roughly what kind of depth of field you’ll get at different distances from your subject.

Time is of the essence, so I suggest you use a combination of these three approaches, depending on what’s possible in the circumstances: you won’t have time to check your app when two African fish eagles are flying past!

When you don’t want it

I’m a wildlife photographer, and my default choice is to shoot wide open because I want the depth of field to be as narrow as possible.

The goal is to draw attention to the subject by ‘separating’ it from the background.

In the image above, I was interested in the bird, not the grass and leaves behind it, so I chose a relatively wide aperture (f/8).

I also happened to be using a long lens (800mm), and the bird was much closer to me than the background.

All that meant that everything behind the bird dissolved into a lovely, smooth green wash, which was exactly what I was looking for.

The background is very important in wildlife photography, and you don’t want anything to distract from the subject.

This includes shadows, branches, other animals or anything else that is just a distraction.

The human eye is drawn to objects that are big, bright, sharp and colourful, so those are the ones you have to try and avoid putting in your background!

The easiest way of doing this is often to use the widest possible aperture, but you may also be able to find a different vantage point just by driving or walking a few feet to the left or right.

When you do want it

Having said all that, there are some occasions when you actually do want to maximise the depth of field.

This shot of a blue wildebeest at sunset is one example.

I wanted the silhouette of the animal to be sharp, but I also wanted the sun and the clouds to be sharp.

There was nothing I could do about the distance to the subject or the background, and I needed my 800mm lens as the wildebeest was so far away, so my only option was to use a narrow aperture (f/16).

These ‘environmental portraits’ seem to be quite fashionable these days, and they’re an excellent opportunity to depart from your usual settings in order to make the whole scene sharp - not just the subject.

What to do if it all goes horribly wrong

Finally, what can you do if it all goes wrong?

There are obviously some situations in which the trade-offs are unacceptable, for instance when you want to photograph a group of animals that are at different distances from the camera, but you still want to blur out a messy background.

One alternative approach that might work is ‘focus stacking’.

This is a method that involves taking multiple shots of the same scene with different focus points and combining them either in camera or in post-processing.

Ideally, you’ll want the images to be identical, which would mean using a tripod.

However, that’s not really very practicable if you’re in a jeep on a game drive in Africa, so you’ll have to find a different solution.

The best way of doing this is probably to make sure your camera is stable (cushioned by a beanbag, perhaps) and then take a number of shots with different focus points.

There are two ways of doing this:

• Select each focus point manually by moving the ‘nubbin’ or the Multi Selector on the back of the camera (if you’re a Nikon user)

• Take a shot focused on the nearest (or furthest) object that you want in focus, then turn the focus ring slightly and take your next shot, repeating the process as many times as you want.

Given the unpredictability of animals and birds, you’ll need to work fast!

Once you’ve done that, you may be able to focus stack in camera, but generally you’ll have to do it in Adobe Lightroom and Photoshop.

Here’s Adobe’s quick guide to focus stacking:

• Select your photos in Lightroom. Load files you plan to stack into Lightroom. In the Grid view or the Filmstrip in the Library module, select the ones you want to stack. (They must be located in the same folder or the same collection.)

• Choose Photo > Edit in > Open as Layers in Photoshop. The stacked photos will display an order number in the upper left corner of their thumbnails, with the top layer being photo 1 and so on.

• Select the layers in the Layers panel. Choose Edit > Auto-Align Layers. Be sure to have Auto selected in the Auto-Align Layers dialog before pressing OK. 

• Select all the layers in the group. Choose Edit > Auto-Blend Layers. In the dialog, select Stack Images and click OK. Now you have your focus-stacked image shown as a layer mask.

If you’d like to order a framed print of one of my wildlife photographs, please visit the Prints page.

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