I already touched on the surface of depth of field in a previous article, and how it relates to the aperture setting used, and as promised then, here’s the follow-up post dedicated to the topic, where I’ll be writing a more in-depth take (yeah I couldn’t resist the little play there) on the theory of depth of field, including all the factors that control it, and some guidelines on how to get the exact depth of field you want for your shot
Alright, so what is depth of field? A basic definition would be: the range of distance (or depth) in an image which appears to be in sharp focus. Simple enough. Just think about it: when you look at a portrait, you will most probably notice that the model’s face is in sharp focus, while the immediate background areas are completely blurred out, well out of focus. On the other hand, look at some wide landscape shot and you will notice that everything in the scene, every little object you can see, appears to be sharply focused. Depth of field is the difference!
The portrait is a perfect example of shallow depth of field, where anything even a few feet behind (or in front of) the model is out of focus, and is perfect for this sort of photograph, where you want the subject to strongly stand out of the background, and grab the viewer’s attention. The term ‘shallow’ refers to the short zone, or depth, in the image that, due to some factors, the lens is able to keep in focus. In the above example, the photographer focuses on the mode’s face, thereby placing his/her face in the in-focus zone, and getting everything outside this zone out of focus
The landscape example is, yes, an example of deep depth of field. In this case, the in-focus zone extends from near to very, very far, again due to some factors, which means the lens is able to keep pretty much everything that you see in focus. It is perfect for shots such as landscapes, where you want everything in the scene to stand out, together as a whole
Check out the examples below. In the shot on the left – everything from the near end of the frame (the lower steps) to the other end of the frame (the higher steps/trees/rest of the stuff on top)…pretty much everything in the frame…seems to be well focused – an example of deep DOF. In the second shot, of the kid…notice how only she is in sharp focus, while the rest of the frame behind her is completely out of focus…yes, that’s shallow DOF
Another example: In the first picture, the bushes near the bottom of the frame (close to the camera) and the landmark building in the distance, and even the HSBC sign in the far distance, are all in focus! That’s pretty deep DOF! In the other example on the right, the focus is on the stone sign on the ground…the street and everything in the background is a nice blur. Shallow DOF!
Like in other aspects of photography, controlling depth of field is up to you, and your creative vision. And like other stuff you think about before you hit the shutter button, you should know what controls depth of field, and how…and know it well enough that it comes naturally, so you don’t lose the shot while you figure out what you need to do to achieve the effect you want
Ok, it’s not that hard to figure out or understand. Put simply, depth of field is controlled by three factors: aperture, camera-to-subject distance, and your lens’ focal length. That’s it. Adjusting any of these three will change how much depth of field your shot will have, and depending on the situation, you can adjust either one or all three to get the result you want. Remember that not always will you be able to adjust all three of these, or even two, but you will definitely notice the depth of field change even after adjusting just one of these variables
So…how does each one affect your depth of field? Here you go
The Factors that Control Depth Of Field
Aperture: Pretty simple (and already explained in an earlier post) – wider aperture (smaller f number i.e. f2.0) means shallower depth of field. And yes, smaller aperture (larger f number i.e. f11) means deeper depth of field. Shooting a portrait? More often than not you’re going to be shooting at a wider aperture. Landscape? Stop down to around f8-11
In the above shots, the focal length was fixed at around 25mm, and was shot at an equal camera-to-subject distance (approx. 1m). The first was shot at f4.0, the second at f8, the third at f18. Notice the sharpness of the laptop (the background) behind the mugs (my subjects). At f4.0, the laptop is a completely blur, and even the white of the cushions on my sofa has a soft, out-of-focus look about it. At f8, the laptop sharpens up, while the cushion looks pretty clear. In the last shot, at f18, you can clearly make out the laptop screen, and maybe even notice that it’s running Lightroom! Look at shot 1 and then immediately at shot 3: that’s how aperture affects DOF!
Camera-to-subject distance: Again, it’s simple – move in closer to your subject for shallower depth of field…and move back for greater depth of field. To make it even simpler…greater camera-to-subject distance=deep depth of field, and shorter camera-to-subject distance=shallower depth of field (I’m getting tired of saying ‘depth of field’!)
In this example, the aperture was set at a constant of f5.6, and the focal length was fixed at around 23mm on my standard zoom lens. The first was shot with the camera around 1.5m from the subject. Notice the laptop again; while it’s not completely sharp, you can quite clearly make out the basic shape of what’s on screen. Compare it to the second, which was shot from around 0.3m from the subject (around my lens’ minimum focusing distance), and see how everything in the background changes into a complete blur! Not a thing can be clearly distinguished in the second shot’s background, right?! Yeah!
Focal Length: Lastly, the focal length of your lens will affect the depth of field. If you’re using a fixed focal length, it’s going to be a pain to switch lenses to just vary the DOF, and you probably might not do that…but if you’re using a zoom lens…well yeah, it’s easy to remember again: wider angle (shorter focal length) i.e. 18mm would mean greater depth of field…and moving to the tele end (longer focal length) i.e. 70mm would mean shallower depth of field
Here, the aperture was set to a constant f5.6, and both shots were taken at around 1m from the subject. In the first, I shot at a wide focal length of 18mm on my standard zoom lens, and the second was taken at 55mm on the same lens. Again, in the first shot, you can clear make out details on the laptop and its screen, while in the second shot, everything is completely blurred out
And that’s pretty much how aperture, distance and focal length controls depth of field
Understanding the Factors of Depth Of Field
In any situation, you will either want to increase your depth of field, or reduce it, right? That’s the basic idea – and that’s pretty much all you need to know how to do, to begin with. I always find it’s easier to understand a theory when you actually use it in a likely scenario, so let’s check out a ‘real life’ example where you will need to control DOF. Ok. You’re shooting a group of people outdoors…the distance between the nearest person and the furthest person from you is around 4m…you want them all in focus, meaning you need a deep depth of field…so what do you do? Easy: use a narrow aperture and/or step back from your subjects and/or use a wide focal length
Ok. In this instance, you probably don’t want to increase the distance between you and your subjects, and appear disconnected from the shot…so stay where you are. It’s outdoors, and there should be enough light to deal with a small aperture… so aperture goes down to f8 (or f11…depends, right?). Lastly, to capture the entire scene, you will have to use a wide angle lens or the wide end of your zoom anyway. Of course, this will also increase your DOF, so get your focal length down wide…18mm? Great. Don’t forget to focus on someone…and hit the shutter. The result should be an image where everyone is in focus. Perfect
Then there’s the other situation, the situation where you will want to reduce your depth of field. Reducing the DOF is what many people refer to as “blurring the background” – that is essentially what it does, so yeah – to blur the background, you can widen your aperture and/or step in closer to your subject and/or zoom into a longer focal length. Assuming you can do all three, you should see a great difference in how blurry your background is. Even one of the three will make quite a difference in the blurriness of the objects behind the subject, as you should’ve noticed in my above example images!
Putting all this into a real life scenario that requires you to reduce DOF – I’m getting bored of the portrait example – let’s say you’re shooting a…piano. You want the first few keys to be sharp, the rest to slowly fade off into beautiful blurriness. Alright. Quickly now…open up the aperture. This will probably help if you have less than sufficient light too – pianos are usually indoors, so the light could be quite dim – so f2.8? f3.5? Ok. Next, you don’t want the entire piano showing in the frame, so zoom in to the telephoto end of your zoom (or use a longer prime lens), say 50mm. Then, step in close to the piano…focus on the front few keys…and shoot. The result should be exactly what you wanted. Alright!
NOTE: These settings I mentioned are just random ones. On some lenses, you might not be able to set an aperture of f2.8 if you zoom in to 50mm…the Canon EF-S 18-55mm has a minimum aperture of a not-so-wide f5.6 when you shoot at 50mm…but I think you get the idea i.e. wider aperture, longer focal length, move in close…and watch that background blur. Opposite settings for the opposite effect. Yeah
Experiment? Exercise? Whatever You Call It!
Ok, to end this post, try this little experiment with some random object in your bedroom. Use the same lens (preferably a standard zoom lens, like a DSLR kit lens), same subject, same lighting conditions…and try placing a secondary object in the background, for comparison
First – set the aperture to f11 (or 16), get your focal length to the wide end of your zoom lens (18mm?), and shoot from approximately 1.5m from the subject. Grab a shot
Next – zoom into the telephoto end of your zoom lens, set the aperture to f5.6 (or wider if your lens can go wider), and move in as close as your lens lets you focus (you should be able to move in to around 0.5m or even a bit closer). Grab another shot
NOTE: In each of the shots, remember to focus perfectly on the subject, nowhere else
Compare the two shots and see how different the background looks. The first one should have the background rather clear at least, if not sharp…and if you have placed a secondary subject in the background, you might be able to make it out or even see it clearly. The second shot should have a completely blurred background, and you probably will not be able to distinguish the secondary subject at all. Due to the different focal lengths and you moving in and out of the subject in each of the shots, the background area will vary…but you can compare the clarity of the visible background to realize how the depth of field was changed in each shot by adjusting those variables
Alright, I hope that this has helped you grasp the idea of depth of field, and how to use it to benefit your shots. It’s not that hard, and don’t try to be too theoretical about it, but DO try to memorize the factors and how it affects DOF (i.e. remember that wide aperture=shallow DOF, not vice versa), so that you can recall the stuff in an instant and get that quick shot before it’s gone. Happy shooting! Until next time
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By Heshan Jayakody All content in this post is my own
- Understanding Maximum Aperture (nikonusa.com)
- PASM: Using Your Camera’s Mode Dial (pixelogist.me)
- Understanding A Consistent Depth Of Field With Varying Focal Lengths (digital-photography-school.com)