Depth of field is without a doubt one of the most powerful tools you have to change the look and feel of your images but it is also one of the most misunderstood concepts in photography.
Last week we spent a morning in the Mara working on depth of field and how various factors will influence the results you out in the field. Before I show you the experiment we did let’s quickly touch on the basics.
The depth of field in an image refers to the acceptable level of sharpness in an image. A shallow depth of field will render a small part of the image in focus with the background being soft and out of focus while a large depth of field will render more of the image, from front to back, in focus. In our courses and workshops I call this the red zone. You’ll see why in the images below.
There are four factors that influence the depth of field in an image but before we get there let’s first look at a basic example.
The first thing you need to decide is what part of an image you want as your subject in the frame and place your focus point on that subject. In the image below the photographer would be aiming at the lion from the right of frame.
In the above example I locked my focus on the lioness’s eye.
By dialling in a large aperture – remember that this is done by selecting a small f-number – I will have a relatively small depth of field, a small red zone.
Let’s now assume that everything stays the same and I want a larger red zone I can dial in a smaller aperture – a larger number – which will render more of the image, from front to back, sharp and in focus.
Pretty simple so far right?
A nice and easy way to remember this is that a small f-number will render a small amount of your frame in focus and that a large f-number will result in a large amount of your frame being in focus. So, everything inside your red zone will be sharp and in focus with everything outside your red zone being more and more out of focus the further it is away from the focal point.
As mentioned earlier there are four factors that influence your red zone in an image with aperture being one of them. The other three are:
- Focal length
- Distance to subject
- Distance from subject to background
During our morning last week we did a practical exercise to show the different results of shooting various focal lengths at different apertures and it was a great way for some of our guests to wrap their head around the concept of depth of field and how they can control this in their image.
We chose a tree, as it would not run away while we were busy, and shot various sequences of images with different focal lengths and different aperture settings. We did not change the distance to the tree so the only two factors that came into play was our focal length and aperture. Also notice that since my focal point was always the trunk of the tree that it is rendered sharp and in focus regardless of what the settings were.
The first was a 70-200mm lens set to a focal length of 85mm.
85mm @ f/2.8
Not a bad look to the image with the mountain in the background being just a little soft and out of focus. If anything the foreground in this image shows a little bit of softness.
85mm @ f/8
Very little if any difference don’t you think? If you look really closely you might pick up a very tiny bit of extra detail in the back but nothing dramatic.
85mm @ f/18
Again, nothing dramatic when compared to the above two images.
Conclusion: In this instance the aperture and focal length is not going to make a huge difference to the resulting depth of field. If I wanted more blur in the background in these images I would have had to move closer to the subject and then take the image.
Next up we did the same exercise with a focal length of 400mm which means we should get more dramatic background blur due to the increased focal length.
400mm @ f/4
At f/4 you can definitely see the shallow depth of field which renders the tree, my focal point, sharp and in focus with the background getting progressively more and more out of focus.
400mm @ f/8
See how the detail in the mountain starts to pop a bit more? This is the result of using a smaller aperture.
And again, with a smaller aperture the red zone, the acceptable zone of sharpness, has been increased and much more of the background is rendered sharp and in focus.
Conclusion: With a longer focal length of 400mm the resulting depth of field becomes a lot more noticeable giving you more creative options.
For the last round of depth of field testing we did the same exercise with a focal length of 600mm.
600mm @ f/4
The shallow depth of field of the super telephoto renders the background detail very soft and out of focus.
600mm @ f/8
The smaller aperture at f/8 still leaves us with a very out of focus background but there is a subtle increase in the detail in the background.
600mm @ f/18
The background is now a little more in focus, albeit still quite soft, and you can see what is happening in the background.
Conclusion: A super telephoto will give you the ability to render your background very soft and out of focus leaving your subject crisp and in focus.
So, which one is better you ask? A shallow depth of field or a nice and large one to render everything in the frame in focus?
There is unfortunately no answer to that question and it is completely up to you as the photographer to decide what the story is that you want to convey in the frame. If you want the focus purely on your subject then use the tools above to render the background silky smooth. If you want more detail behind your subject because it adds to the story do what you have to do to create a large red zone.
Here are a few things to keep in mind when working on creating depth of field in your wildlife images:
- It’s difficult to create a very soft background with a small focal length. Use these to tell environmental stories.
- Getting closer – everything else remaining the same – will render the background more out of focus.
- Don’t forget that you can normally control at least 3 of the variables which allows you the creative freedom to capture any given scene.
- You don’t always have to shoot at the largest aperture available. Sometimes a bit more of a red zone will make for a stronger image.
The best place to learn is out in the field so when you are next out there try this exercise with your own lenses so that you can see the results for yourself. With a little bit of practise you will get a very good understanding of the variables that you have to play with and also get a feeling for the look and feel that your lenses will give to your images. We do these kind of things on all of our safaris and workshops so if you are keen to learn with us you know what to do!
One final example of how understanding and applying the variable discussed above can help you create stronger images in the field.
Shot at f/5.3 on a 300mm lens from about 25 meters.
Good luck, keep shooting and leave me a comment if you have any questions!
Until next time.