Understanding Depth of Field
Depth of field refers to the range of distances that appear sharp in your image. It is the precise area in front of and behind the subject that will appear sharp and hence the focal point of the photograph.
Some images may have very small zones of focus with a blurred background and foreground which is called shallow depth of field. Others have a very large zone of focus meaning we can see details in the far distance behind the subject which is called deep or large depth of field.
There are three main factors that will affect how you control the depth of field in your image; aperture (f-stop), distance from the subject to the camera, and focal length of the lens on your camera.
But before I tell you the techniques let’s look at how manipulating depth of field is an important tool when composing an image that portrays a story or emotion.
When to use Shallow Depth of Field to get better images
Using a shallow depth of field is a good way to make your subject stand out from its background and is commonly used in portrait photography or wedding photography to ‘isolate’ the main subject.
Shallow depth of field can also be useful in wildlife photography and can also be effective for sports photography when you want to separate the star athlete from the background action.
If it is an expression on the mother of the brides face, the hand details as the basketballer dunks or the look of bliss on the kittens face as it sinks into a soft background- if your focal point is small and distinct from the rest of the photograph, you’ll want to use shallow depth of field. It’s a great technique for focussing on singular moments and gestures of individuals.
Shallow depth of field is also common in commercial product shots for striking subjects that stand out from the rest.
When to use Depth of Field for to Create Better Images
Depth of field is a great technique for capturing details around your focal point or if the whole pictures is equally important. It is a great technique for capturing the majesty in landscapes or the hustle of cities, where you want the viewer to be able to spot a lot of detail and for the image to be in focus through out.
In landscape photography most photographers want to capture as much as the scene as possible by keeping the image sharp in the distance and foreground, and to the left and right of shot as well.
Cityscapes, such as looking down long tunnelling Italian streets, or the rooftops of Paris as the billow back or seeing deep into the hustle and bustle of a Thai street market can all be captured with a lot of fascinating detail with a deep depth of field.
You might also consider depth of field at festivals, protests and parades where you want to show how huge the event was (and then pull into a shallow depth of field to captuer individuals in the scene).
Aperture & depth of field
Aperture is the easiest and for many photographers the primary way to control your depth of field as you set up your shot. Aperture refers to the amount of light allowed to enter your camera through a mechanical iris made up of tiny blades.
In short the lower your f-number, the larger the iris and the smaller your depth of field. Like an open eye the camera is looking broadly across the scene and not deeply into the background.
Large aperture or a small f-stop (i.e. f/2.8) = Shallow depth of field
Small aperture or a large f-stop (i.e. f/18) = Deep depth of field
Adversely, the higher your f-number and the smaller the aperture, the larger your depth of field. They camera iris like an eye is squinting to make out a single spot and as much detail in front of it and behind it as it can.
Keep in mind that as aperture size is also important to light. If you are trying to increase your depth of field by reducing aperture size to say f11 you will also need to increase (slow down) your shutter speed which could make your image blurry. Try a tripod to keep the camera still or you could change the ISO setting (make it higher but beware that the highest it is the more the grain).
Focal length & depth of field
Focal Length is concerned with the capability of a lens to magnify the image of a distant subject with something like a long telephoto lens. The distance between the lens length and the senor is the focal length. Wider lenses have shorter focal length while longer (i.e. telephoto) lenses have longer focal length.
The longer you set your focal length the shallower the depth of field. So if you stand far from your subject and zoom in, you are more likely to get a shallow depth of field with a sharp subject and very little discernible background.
Using focal length to manipulate depth of field is perhaps the trickiest way for beginners and your best bet is probably to do some practical exercises with your camera. You will need a mid to long lens to practice this (it is very hard to get a shallow depth of field with a wide angle lens, even if the aperture is wide open).
Place your subject 10 metres away, using a focal length of 50mm at f/4. Your depth of field range would be from 7.5 -14.7 metre giving you about 7.2 meters of depth of field.
If you zoom into 100mm from the same spot, the depth of field should change to 9.2-10.9m for a total of 1.7m of depth of field.
If you move to 20m away from your subject using the 100mm lens, your depth of field is almost the same as it would be at 10 meters using a 50mm lens.
One thing you may notice is that depth of field is not usually distributed equally in front and behind the subject when manipulating it with a lens and focal points, but as your focal length increase it does become more equal.
Moving yourself & Depth of field
The closer your subject is to the camera, the shallower your depth of field becomes. Therefore, moving further away from your subject will deepen your depth of field.
This can be fun to play with if you have a long and a short lens as this works in conjunction with the lens’ focal length.
Get in relatively close with a relatively long focal lens as you manually focus look for that sweet spot of a sharp image floating in that lovely bokeh blur. Try the same shot stepping back and forward, zooming in and out. For the purpose of the exercise keep the aperture at a steady mid F-top like f8.
Some notes and tips
If your camera came with a wide kit lens, you may not be able to get really great shallow depth of field such as the bokeh blur. The reason is that the lens probably stops at about f/4. A longer lens will give you more range of f-stops to play with and more options for depth of field.
If you are using a closed aperture (a high f-stop) to capture a deep depth of field, especially at sunset or night, you will definitely need a tripod as you will need to slow the shutter speed. If you put your camera on aperture priority it should slow down to let in light automatically.
Most photographers find each of their lenses have 2 or 3 sweet spots as far as focal length goes meaning they pull focus to that familiar length and suddenly there is that magical surreal sharpness at a specific distance in front of them.
These sweet spots also depend on the camera they are using and the type of photographs they like to take. Practice with all three techniques to get to really know your camera and lenses and discover how they best get you the depth of field you want in different situations.
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