What is Depth of Field ?
Depth of Field (DOF) is the term used to describe the areas before and beyond the point of focus that appear sharp. Although the lens can precisely focus only at one distance, the degradation in sharpness in the areas in front and rear of the focused distance is too subtle to be visible to the human eye. It is the area around the subject of focus that look sharp that we say that they are within DOF.
Depending on various factors depth of field can be small or large.
Small (shallow) depth of field means basically that only a small portion of the area around subject will appear sharp, while everything else will appear fuzzy (top example).
Large depth of field means that most of the image area will appear sharp, regardless of the chosen subject to focus on (bottom example).
Why is depth of field so important ?
Controlling the DOF gives the photographer creative freedom do control which areas of the photo should be in sharp focus, and which shall be blurred (out of focus). Although it does not sound like a big deal, it is a powerful tool when composing an image. Ever heard the expression less is more ? This is especially true in portraits.
If you examine deer portrait to the left you will notice that while the deer is in sharp focus, the background is blurred, to make sure that it does not distract the viewer. This is one of the ways a photographer can emphasize the subject by making it visually stand out.
In the following section is the pictogram describing how this photo was taken. The main point was to use shallow DOF to make sure that the background is out of focus. This will often be the case for most portraits.
Landscapes usually follow exactly the opposite rule, and try to maximize DOF as much as possible. This will ensure that the beauty of the environment is captured in all its glory.
How to control depth of field ?
These are the key factors that regulate the depth of field:
All of those components work together towards obtaining the creative effect the photographer tries to achieve. So, how do specific components impact DOF ?
Subject placing – basically, a rule of thumb is, the closer your main subject is to your lens and further it is from its background, the smaller the chance that both of them will be within the same DOF. You can use this rule if you want to visually separate your subject from the background and make it stand out.
Lens focal length – generally speaking, the rule here is that lens with longer the focal length have shallower depth of field, and vice versa. Although this rule is most used with digital cameras that use interchangeable lens, such as dSLRs, and some prosumer models, users with digital compact cameras can too benefit from this rule. How ? Simply put, if your digital compact camera has ANY optical zoom (the more the better), make sure that you zoom all the way in when taking a photo.
Lens aperture – if you do not know what aperture (f-number) is, please check out our article about aperture first. In terms of depth of field, note that increasing the aperture (lowering f/nr) lowers the DOF. So, the same lens at aperture of f/2,8 has much shallower depth of field then at f/11. For the cameras that do not allow control over aperture such as compacts, putting the camera in portrait mode (for taking portraits of people), will increase the aperture, resulting in shallower DOF. Also if you want larger DOF, put the camera in the mode for photographing landscapes.
Sensor size – various cameras come with different sensor sizes. We will not discuss all sensor sizes, as it would draw focus from the article. Suffice to say, assuming we use the same lens on cameras with different sensor size (e.g. dSLRs with APS-C and full frame sensors), the camera with smaller sensor will experience larger depth of field.
If you are a digital SLR user and want:
- large DOF (all sharp) – use lens with smaller focal length (wide angle lens (18mm) to normal (50mm)), set to small apertures (e.g. f/11-f/32)
- shallow DOF (blur background) – use longer focal length lens (telephoto welcome (75mm and over)) set to wide aperture (e.g. f/2.8-f/5.6), and make sure there is sufficient dista
nce between your main subject and its background.
… and if you are a digital compact user:
- large DOF – zoom all the way out, set camera to landscape preset, to maximize effect
- shallow DOF – zoom all the way in, set camera to portraits preset, and make sure there is sufficient distance between your main subject and its background.
Handy DOF Tools
There are more and more tools and gadgets available to help photographers and enthusiasts alike. We have browsed a web to check out if there are any that are handy with helping calculate DOF. This is what we have stumbled upon:
1. There is an excellent online calculator for calculating the DOF:
DOF Master’s Depth-of-Field Calculator – just input your camera, lens, and other parameters and it calculates the nearest point in focus, the furthest and hyperfocal distance. Only remark is that you have to have Internet access in order to use it. But it’s cool.
2. If you prefer more hands on, and a tool you can take with you, be sure to check out ExpoAperture, Depth of Field Guide Combo Pack from ExpoImaging.
3. If you are one of the lucky iPhone users, be sure to check out iFotobacus application.
How to creatively use depth of field ?
There are numerous ways to creatively use depth of field, limited only by your imagination. Here are a few ideas to get you started:
1. Create sensual flower macros (soft focus=shallow DOF)
2. Razor sharp landscapes (large DOF – use hyperfocal distance)
3. Take a photo of a person just slightly out of focus
4. Practice portraits until you get the hang of it
Go out there and experiment. And let us know how it went ;-). Post comments and share your experiences with others.
More resources on DOF
If you would like to know more about depth of field, and some of the techniques how to extend it (i.e. through multiple exposure) we suggest to check out the following books:
1. Photographic Multishot Techniques: High Dynamic Range, Super-Resolution, Extended Depth of Field, Stitching