Open wide - the use of aperture settings in wildlife photography

By Chad Cocking

The first step to improving one’s wildlife photographic results is to move away from the camera’s fully automatic settings and start taking some form of control over the images you produce. This might seem like a daunting prospect, but I can promise you that it is not nearly as difficult as it may sound as long as you understand how the different settings will affect the images that you are taking. This blog post will focus on explaining how the various aperture settings of the camera can be used in wildlife photography, and what settings are best to use.

This is an image of a  female leopard walking down a road and photographed with a wide aperture, demonstrating how aperture can be used to control the depth of field within an image

A question that I am frequently asked is what camera mode I would recommend shooting on for wildlife photography. Now, while being so au fait with one’s camera and its settings to be able to shoot in complete manual exposure mode is an admirable goal, I have found that for most general wildlife photography, this setting is simply not practical.

As a result, I have chosen the adoption of the semi-automatic Aperture Priority mode when I am out in the wilderness taking photos. This mode can be found on the camera dial under different abbreviations, but the most common of these would be A-mode in Nikon, and Av-mode in Canon.

When photographing with aperture priority, you tell the camera what aperture setting you want, and it will calculate the required shutter speed to produce a correctly exposed image. This means that although you are taking control over the aperture settings, the camera will still automatically make some of its own adjustments, hence the term semi-automatic.

It is all well and good knowing that you need to shoot in aperture priority, but what exactly is this aperture referring to, and more importantly, how will it affect your wildlife images?

The aperture refers to the size of the diaphragm within the lens that controls how much light makes it through the lens to reach the camera’s sensor. This means that the wider the aperture, the more light reaches the sensor, and the faster the shutter speed can be. As the diaphragm closes and less light is allowed through, the camera has to compensate for this by leaving its shutter open for longer, resulting in a slow shutter speed that is seldom desirable in wildlife photography (slow shutter speeds are a major cause of blurry photos).

By shooting this scene of an elephant spraying water out of his trunk with a wide-open aperture (f/4.0 at 1/2000 sec, ISO 800), I was able to get a fast enough shutter speed to be able to freeze the spray of water.

In photography, the aperture is described using an f-number, and it is this number that you have to set when shooting in aperture priority. There is an inverse relationship between aperture size and the f-number - written as f/xx.x - so that the smaller the f-number, the wider the aperture. This means that a lens with an aperture of f/2.8 will have a wider aperture (and allow more light through, thus leading to a faster shutter speed) than a lens with an aperture of f/6.3 (resulting in slower shutter speeds and more chance of a blurry image).

Another important effect of adjusting the aperture relates to just how much of the image is in focus, in what we refer to as the depth of field. The wider the aperture, the shallower the depth of field becomes, so that a lens set to f/2.8 will have a shallower depth of field compared to that same lens set to f/11.

The greater the depth of field, the more the scene will be in focus, whilst conversely, the shallower the depth of field, the smaller the in-focus area will be. Thus, by controlling our aperture, you not only control how much light is let through the lens, having a direct consequence on the camera’s shutter speed, but you are also able to control just how much of a scene is in focus. Luckily for us, both of these aspects can be used to great effect in wildlife photography.

This series of images of the same leopard resting on a mound clearly illustrates the effect that changing the aperture can have on determining the depth of field in the image. This first image has a lovely smooth background as a result of shooting at f/4.0 at 1/3200 second

As the aperture is closed down to f/9.0, not only does the background start looking less smooth, but the shutter speed has decreased down to 1/640 second

Shooting at an aperture of f/18.0, the background is now taking on a great deal more detail, and the shutter speed is down to a slow 1/160 sec, greatly increasing the risk of motion blur

With all of this in mind, what is the best aperture setting to use when we are taking wildlife photos? Although there is not one single setting for all circumstances, my preference is to set my aperture wide open (the smallest f-number) for the simple reason that by doing this, and having the lens’s aperture as wide as it can be, I am ensuring that I will have the fastest shutter speed on my camera. As a result, I greatly limit the chance of a blurred image caused by camera shake, or by movement of the animal.

For me, the added advantage of this approach is that, with the wide-open aperture, I have the shallowest depth of field available, and this will lead to a wonderfully soft, out of focus background (called the bokeh). This bokeh effect really allows your subject to stand out from the background, producing eye-catching imagery.

A hyena cub stands out completely from the smooth background, drawing all of the attention to the animal as it is now free of background distractions (f/4.0 at 1/400 sec on ISO 800)

This male lion was roaring in very low light; the wide open aperture of f/4.0 not only allowed a fast enough shutter speed to freeze the action, but also blurred the background due to the shallow depth of field

The downside of shooting with your aperture wide open is that because the depth of field is so shallow, your focus has to be spot on to make sure that the most essential parts of the subject, namely the eyes, are in focus. If your focus is only a little bit out (especially when the animals are close by, or you are using a long telephoto lens) then you risk ending up with an image that is out of focus on the most important parts. In cases such as this, it is worth closing down your aperture to f/7.1 or f/8 to ensure the that depth of field is sufficient.

An example of the downside of photographing with a wide open aperture, and a concurrent shallow depth of field. I focused on the chest of this hyena that was only a few metres away from me, but with an aperture of f/4.0, the depth of field was so shallow that its entire head is out of focus

Even at an aperture of f/5.0, the depth of field on this leopard cub was extremely shallow, so my focus needed to be spot on to ensure that the most important parts of the cub were in focus - its eyes and its head

Other instances when a greater depth of field is needed (and hence the selection of a smaller aperture or larger f-number) may include times when you are photographing various landscapes or scenes where there are multiple animals in shot. In both cases you would wish to have the entire scene in focus, and would set the camera’s aperture to increase your depth of field. The slower shutter speed that these aperture settings will give you tends to be much less important when it comes to photographing inanimate landscapes, so they are not seen in as negative a light as they would be for scenes involving more active animals.

Increasing the depth of field by using an aperture of f/13 allowed me to get detail in both the giraffes and the setting sun. At a smaller f-number either one of the two would have been blurry and out of focus

Experience is often the best teacher, and the easiest way to learn more about the effects of the aperture on your images is to grab your camera and go out and play around with the various settings. The subjects can literally be anything found out in your garden or local park, photograph them to see how the different apertures not only affect your depth of field, but also the effect that these changes have on your shutter speeds. This latter aspect will be the topic of discussion in our next blog.

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