KVL Production
Depth of Field Guide
Training Document May 2014
Prepared by April Bailey
Guide for Creating a Shallow Depth of Field with a Digital Camera
Depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear
acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the
decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the areas
outside the DOF are less perceptible under normal viewing conditions.
Although it is easy to obtain a deep depth of field with most digital cameras and surprisingly difficult to
obtain a shallow depth of field. This has to do with the relationship of film formats/sensor sizes to the focal
lengths of lenses used. It is important because with the right depth of field, you can make your subject stand
out against the foreground and background in a pleasing way that isolates and emphasizes the subject. In
recent years, many independent filmmakers have been excited to use DSLRs for HD video production since
they have the bigger sensors that help create a shallow depth of field to maintain the more pleasing "film
look," while still allowing for wide angle work. This guide will cover important aspects and technical
information for how to obtain a shallow DOF in your video footage.
In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other
cases, a small DOF may be more effective, emphasizing the subject while de-emphasizing the foreground
and background. In cinematography, a large DOF is often called deep focus, and a small DOF is often called
shallow focus. Digital techniques, such as ray tracing, can also render 3D models with shallow depth of field
for the same effect, but I am focusing on digital video camera work in this guide.
Understanding Digital Video Cameras
In the days of film, just about everyone used 35mm film and lenses with the same focal length range; now, in
the digital age, sensor sizes vary from tiny to full-frame 35mm sized and even beyond. There is no
standardization on sensor size, and each size comes with its own requirements for focal lengths. Now that
digital has taken over, sensors are smaller than film was, the lenses are shorter, and the depth of field is
generally deeper. If you want everything in focus all the time, this is great --but when you are trying to
attain the painted background (blurred) film effect or “bokeh” in your work, this can be a challenge.
However, there are some nice tricks of the trade that can be used with almost every camera.
KAUST Visualization Laboratory
King Abdullah University of Science & Technology
KVL Production
Training Document May 2014
Depth of Field Guide
Prepared by April Bailey
Digital Camera Sensors
The image sensor in a digital camera is a device that converts an optical image into an electronic signal.
Most digital still cameras use either a CCD image sensor or a CMOS sensor. Both types of sensor carry out
the same task of capturing light and converting it into electrical signals. The larger the sensor = more light =
more detail, and thus = more image information recorded. Both CCD (charge-coupled device) and CMOS
(complementary metal-oxide semiconductor) image sensors start at the same point -- they have to convert
light into electrons. One simple way to think about the sensor used in a digital camera is to think of it as
having a 2-D array of millions of tiny photosensitive cells, which transforms the light into electrons. Both CCD
and CMOS devices perform this task using a variety of technologies.
CCD: Charge Coupled Device
is an analog device.
CMOS: Complementary Metal–Oxide–
Semiconductor this also called as activepixel sensor (APS)
In digital photography, the image sensor format is the shape and size of the image sensor. There are various
sizes of the sensors available. All compact cameras have tiny sensors, and are not able to produce high
quality videos (little light divided my so many pixels) while full frame sensors are the best, but the size and
the price of the camera can greatly increase. APS formats used in DSLR cameras however, really reduced
the price and size, while maintaining the capability to create very good quality photos using DOF.
KAUST Visualization Laboratory
King Abdullah University of Science & Technology
KVL Production
Depth of Field Guide
Training Document May 2014
Prepared by April Bailey
Sensor Size & Format
Sensor size governors the crop factor and focal length of your camera, thus it determines the angle of view
of the lens used with a camera. Image sensors that are smaller than the 24 mm × 36 mm image area of fullframe 35 mm camera, therefore leads to a narrower angle of view.
When the angle of view gets narrower, there is possibility of losing some exterior part of the image. This is
called cropping or “crop factor” which depends on the image sensor size inside each different camera.
KAUST Visualization Laboratory
King Abdullah University of Science & Technology
KVL Production
Depth of Field Guide
Training Document May 2014
Prepared by April Bailey
Focal Length (mm)
There is a measurement marked on the exterior of each lens that designates its focal length. Focal Length is
measured in millimeters. The higher the focal length of the lens, the further away your lens will reach and
the easier it will be to create a shallow DOF. For Example, a 24 mm lens will require you to put more
distance between your subject and your background than a 200 mm lens.
Capturing a subject the same size with different focal length lenses yields very different results. When using
a wider lens, more of the background is depicted. In contrast, with a telephoto focal length, the background
view is narrower and will appear closer to the subject (compressed).
The longer the focal length, the shallower the DOF you will have. A 20 mm lens will have deeper DOF than a
50 mm, which will have a deeper DOF than a 100mm, etc. With really short lenses, like 4 mm, you will have
immense depth of field. With long lenses, like 400mm, you will have miniscule depth of field.
KAUST Visualization Laboratory
King Abdullah University of Science & Technology
KVL Production
Depth of Field Guide
Training Document May 2014
Prepared by April Bailey
Lens Speed
Lens speed is how fast the shutter opens and closes. The speed of the lens determines how much light is let
in through the lens to reach the image sensor. A fast lens lets in more light to the sensor. A slow lens lets in
less light. Because more light can get in when using a higher speed lens, you can often get better images in
available light – especially when that light is relatively dim. This allows for more exposure options in low light
and isolated subjects with nicely blurred backgrounds. The full range of shutter speeds traditionally is:
Shutter Speed 1/4 second 1/8 1/15 1/30 1/60 1/125 1/250 1/500 1/1000 1/2000 1/4000
f/stop
f/45
f/32 f/22 f/16 f/11 f/8
f/5.6 f/4
f/2.8
f/2
f/1.4
It's pretty clear that the shutter speed, doubles and halves throughout the range. The wider the aperture,
the more light that gets in to the sensor. “Fast” apertures – like f/1.4 or f/2.8, ensures that the f-stop will be
wider than a slower lens because the camera is able to open the diaphragm much quicker allowing more
light to enter. By opening the aperture all the way up in a low-lit setting and keeping a fast shutter speed
you can create a shallow depth of field.
Aperture (Iris) Setting
We refer to lens speed as the maximum aperture of the lens diameter of the open circle or diaphragm inside
the lens. This diameter is expressed as “f-stop” or “f/#” such as f/2.8 or lower f/1.8. The f-number of a given
lens is a mathematical expression used as an aperture designation across all lenses of different focal lengths
that allows us to get the same exposure values.
As the f-stop number gets bigger the f-stop aperture gets smaller.
The aperture setting determines the size of the opening (iris) that lets light through to the CCD. Adjusting the
aperture to a setting that allows for the most light will create a shallow DOF. A small aperture setting results
in a deeper DOF and a large aperture setting provides a shallow DOF. If you are shooting a panoramic
scene and want a large area in focus, you would use a smaller aperture to maximize the depth of field. If you
want your subject to stand out from the background by being the only thing in focus, you would choose a
larger aperture to decrease the depth of field. A smaller aperture setting allows less light through, so you
may have to make other adjustments to compensate, such as adding lights or slowing the shutter speed.
The wider that the f-stop is open, the more that light can enter the lens. At f/2 (small number, big aperture),
you will have comparatively narrow depth of field, with little in focus on either side of your focus point; at
f/16 (big number, small aperture), you will have comparatively more depth of field, with more subject
matter in focus on either side of your focus point. . Generally a large maximum aperture F2.8 or lower is
good, but F1.8 or lower is better. The lower the f-number = the wider the aperture = faster shutter speed =
the smaller the depth of field.
The Effect of Subject Distance on Depth of Field
Subject distance plays a big part in determining the possible size of depth of field. The closer you are to your
focal point, or subject, the less depth of field is possible. The further away you are, the more depth of field
you will have; however, if the subject is very far from the camera and you zoomed in on them you can
achieve a nicely blurred background if the background 2/3 behind the focal point. Also, if the subject is very
KAUST Visualization Laboratory
King Abdullah University of Science & Technology
KVL Production
Depth of Field Guide
Training Document May 2014
Prepared by April Bailey
close and the background is very far from the subject, you will also be able to obtain a bokeh (blurred)
effect.
To illustrate this effect, hold your hand at arm's length in front of your face. Even when focusing on your
hand you can probably see a good bit of the surrounding environment in reasonably clear focus. Slowly
move your hand towards your face until you reach the half-way point. Notice how much less of the area
surrounding your hand is in focus. Continue moving your hand towards your face until it is as close as your
eyes can focus on it. Very little of the area surrounding your hand can now be seen. There are depth of field
calculators online that can be used to plan out your shots using various focal lengths with f-stop and
distance calculations, such as: http://www.dofmaster.com/dofjs.html. However, it will become intuitive
once you spend time mastering the technique.
Technical Tips for Obtaining a Shallow Depth of Field
1. Decide on the lens length, camera-to-subject-to-background distance.
i. Use a shorter lens (like 50 mm) lens when the camera is very close to the subject
ii. Use a long lens (like 200 mm) and have the background in the far distance
2. Frame the shot using one of these techniques:
a. Move as far away from the subject as possible and then zoom in all the way using manual
focus for a background with a soft “painted” background created with a shallow DOF. Be sure
to use a tripod to steady the camera for the long zoom range. Can you move away from the
subject and zoom in to frame the shot? Can you obtain an angle where there is a very distant
background in the frame?
b. Move very close to the subject as possible and frame the shot to include very distant
background lights (creates the bokeh effect). Are you close to the subject? Can you obtain an
angle where there is a very distant background in the frame?
3. Use a fast lens with the lowest aperture possible.
a. Turn up the speed of the lens and turn the exposure/iris down to the lowest f-stop you can
use and still see the subject adequately. Ask yourself how wide of an f-stop you can open the
aperture up to?
b. Add more lighting in the scene if necessary.
4. Use a lens hood to block light into the camera
5. Add a neutral density filter (or nylon cover) over the lens to block out some light going into the
camera and allow for a larger aperture.
6. Use an overhead scrim to shade the subject and allow for a larger aperture in the focused area.
KAUST Visualization Laboratory
King Abdullah University of Science & Technology