Depth Of Field Explained

One of the most important creative considerations in photography, if not the most important, is control of Depth of Field.

What is Depth of Field?

When making an image you must focus on something. A certain amount of the image behind and in front of the point of focus is also reasonably sharp until it becomes blurry. This is called the zone of “Depth of Field” (DoF). DoF is used to determine the most important point in the image, but also to control the amount of the image that is also sharp (and how much) and the amount of and speed of transition to blur.

DoF is made up of three parts;

1) The fully sharp zone, also known as the plane of best focus,

The focus point is pretty clear in this image. The thin plane of focus and strong blurring of the background add a sense of subject separation.

The focus point is pretty clear in this image. The thin plane of focus and strong blurring of the background add a sense of subject separation.

2) The zone of transition, where fully focussed sharpness starts to become less sharp (softer), and how quickly, depends on the distance to the subject, the subjects distance to their background and the aperture chosen (most transitional DoF falls behind the point of focus).

In this image, the transition of DoF is as important as the point of perfect focus. The point of best focus is the back of the man's Kimono, but more important to the image is the woman facing us, who is not fully in or out of focus. She is caught well enough in the  transition  between the two.  This use of transitional DoF is often referred to as "Bokeh" (see below) or the "character" of focus transition and blur and will vary by lens, aperture, distance and light.

In this image, the transition of DoF is as important as the point of perfect focus. The point of best focus is the back of the man's Kimono, but more important to the image is the woman facing us, who is not fully in or out of focus. She is caught well enough in the transition between the two. This use of transitional DoF is often referred to as "Bokeh" (see below) or the "character" of focus transition and blur and will vary by lens, aperture, distance and light.

3) The out of focus area, where sharpness is lost, becoming true blur. This is often mistaken as the only place where “Bokeh” shows up in an image. Bokeh (see below) is actually the character of both the transitional and out of focus areas and how they relate.

This image made up of mostly sharply focussed detail and soft out of focus blur with very little transition. Close-up images often transition very quickly as close focus distance DoF decreases dramatically (becomes shallower) due to increased magnification.

This image made up of mostly sharply focussed detail and soft out of focus blur with very little transition. Close-up images often transition very quickly as close focus distance DoF decreases dramatically (becomes shallower) due to increased magnification.

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How strongly a subject stands out from their background is called subject separation. Strong subject separation is what we usually define as “portrait style” photography. This makes a hero of the focussed subject and blurs the rest away into smooth softness.

Although this image is not an obviously strong example of a subject "jumping out" against it's background, it still heavily relies on clear  subject separation  to work.

Although this image is not an obviously strong example of a subject "jumping out" against it's background, it still heavily relies on clear subject separation to work.

Good (or strong) separation is usually the result of shallow or very shallow DoF, but light, texture, contrast and colour can also help to separate the subject from their surroundings.

The 3D look of this image comes as much from shallow DoF as it does from the contrast of the well lit, textural, main subject to the darker background and surroundings.

The 3D look of this image comes as much from shallow DoF as it does from the contrast of the well lit, textural, main subject to the darker background and surroundings.

How much depth of field sharpness, subject separation, focus transition and full blur is present in an image, depends on a few elements that are (usually) under your control;

  1. The lens Aperture value you select is the first and often most powerful.

  2. Changing magnification by changing the distance you are from your subject or/and “zooming in or out” with the lens. Increasing magnification either way reduces perceived DoF and visa-versa.

  3. The distance your subject is from their background** is also important here. Increasing the distance the subject is from their background increases DoF and visa-versa*.

  4. Perceived compression or expansion of perspective. This does not necessarily change the actual DoF of an image but it heavily influences how we perceive it.

    *Relative distance control is really important. if you are closer to your subject than they are their background, you will increase perceived subject separation and the reverse is true.

**It is important to remember that the majority DoF falls behind the point of focus, not in front of it.

1. Aperture Settings

Lens aperture settings are the most important, direct and practical DoF control.

Aperture settings come in full value settings of f1.4, 1.8, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, each one halving DOF (as you use smaller numerical values) and double the amount of light let through to the sensor (they are part of the exposure control triangle of Shutter Speed, ISO and Aperture).  Thanks to modern electrical camera controls, there are also 1/2 or 1/3 settings available between these full settings, but it is generally best to just think in full value settings at this stage.

Below is an example of some of these settings in action (these are only some of the full aperture settings, ignoring the third and half values also).

(If you use a zoom lens you will probably not have these first two apertures available)

                                                                         f 1.8                                                                                

The focus point is the face of the first statue and that is basically all that is sharp. The rest of the image is pleasingly smooth and soft, making the front statue the clear "focus point" of the image. This is true  portrait  style technique emphasising maximum  subject separation .

The focus point is the face of the first statue and that is basically all that is sharp. The rest of the image is pleasingly smooth and soft, making the front statue the clear "focus point" of the image. This is true portrait style technique emphasising maximum subject separation.

f 2.8       

The first statue is still the obvious focus point and is now fully in focus, but the other statues are starting to become more coherent. This aperture is starting to include more background detail (reducing separation and increasing transition), but this is still a shallow DoF  portrait  style image. The  Bokeh  characteristics of the lens are important i this style of image.

The first statue is still the obvious focus point and is now fully in focus, but the other statues are starting to become more coherent. This aperture is starting to include more background detail (reducing separation and increasing transition), but this is still a shallow DoF portrait style image. The Bokeh characteristics of the lens are important i this style of image.

(All lenses will have the following settings)        

f 5.6

The image is now starting to tell a story now, showing all of it's elements, even if they are not all completely sharp. This is probably the least effective aperture value for this type of photo as it neither separates one element (a  portrait  style photo), nor shows all of them in sharp focus (a  landscape  style photo). The  transition  from sharp to soft is important here.  If you have a zoom lens and cannot use a wider aperture than this, there are other techniques you can use to make increase separation (see below).

The image is now starting to tell a story now, showing all of it's elements, even if they are not all completely sharp. This is probably the least effective aperture value for this type of photo as it neither separates one element (a portrait style photo), nor shows all of them in sharp focus (a landscape style photo). The transition from sharp to soft is important here. If you have a zoom lens and cannot use a wider aperture than this, there are other techniques you can use to make increase separation (see below).

f 11           

Almost all of the statues are now reasonably sharp. The image is starting to become a true  landscape  style image. Even though the village in the background is not fully sharp, the viewer will now accept it as part of the overall image.  Because DoF falls mostly behind the point of focus, focussing on the last statue would likely render the front one as fully soft, which is why landscape photographers usually pick out a foreground subject to focus on, letting the transition of deep DoF capture the background.

Almost all of the statues are now reasonably sharp. The image is starting to become a true landscape style image. Even though the village in the background is not fully sharp, the viewer will now accept it as part of the overall image. Because DoF falls mostly behind the point of focus, focussing on the last statue would likely render the front one as fully soft, which is why landscape photographers usually pick out a foreground subject to focus on, letting the transition of deep DoF capture the background.

f 22

Now even the little town in the background is starting to look in focus. These photos were taken of small (5cm tall) statues  up close , exaggerating the effect of shallow DoF by increasing magnification. The aperture will often slightly soften an image through Diffraction (see lens aberrations below).  This image is using true    landscape    technique although the very close focussing distance (see below) has not allowed all of the elements to be fully sharp. Now scroll back up to the top, looking at the village in the background as you go.

Now even the little town in the background is starting to look in focus. These photos were taken of small (5cm tall) statues up close, exaggerating the effect of shallow DoF by increasing magnification. The aperture will often slightly soften an image through Diffraction (see lens aberrations below). This image is using true landscape technique although the very close focussing distance (see below) has not allowed all of the elements to be fully sharp. Now scroll back up to the top, looking at the village in the background as you go.

Most depth of field falls behind the point of focus, so if the nearest foreground does not look very sharp until apertures f5.6 or smaller, that is normal.

Looking at the images, you will see a clear pattern emerging. 

When you use a wide aperture (small number values like f1.8 to f2.8), the depth of field will be very shallow. At f1.8 it will look razor thin, making accurate focussing difficult and very important, especially at very close focussing distances. 

As the aperture values become smaller (bigger numbers like f8 to f22), the depth of field increases or becomes “deeper”. The terminology is confusing I know, but it is what it is.

Tip. An easy way of remembering the aperture values and how they effect depth of field is to think of them as measurements of DoF distance or of the number of bottles/feet/fence posts/inches/trees that are in focus when focussing down a line of them. A bigger number is more DoF or more “in focus” distance (f2.8 could be 2.8 bottles sharp, f11 is 11 bottles etc). This actually has nothing to do with what the numbers mean, but it helps to remember which way they work.

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2. Magnification

If you increase magnification by either changing the strength of your lens or actually moving, you reduce DoF and the reverse is true. The more magnification/closer you get, the shallower the DoF will be. The further away you move or more you zoom out the greater the DoF. These methods can help control DoF, but they both act a little differently (see also point 3 below).

  • If you move physically closer to the subject, using the same lens focal length, your DoF will get shallower because you are increasing magnification and at the same time increasing the relative distance between the subject and their background. This increases subject separation. The opposite is also true, moving further away from the focussed subject reduces magnification and decreases the relative distance from the subject to their background (see relative distance below).

  • If you zoom in using a longer lens, the DoF will look shallower and the image more compressed (flatter), but the distance from subject to it's background will not change. Using a wide angle lens will decrease magnification and expand perspective (see below), making effective DoF deeper, but again the actual distance from the subject to their background does not actually change (see relative distance below).

A combination of a long lens and close shooting distance has created very shallow depth of field and strong, clean subject separation.

A combination of a long lens and close shooting distance has created very shallow depth of field and strong, clean subject separation.

A more distant subject and less powerful lens has given this image deeper DoF. The front of the building and the distant clouds are both in sharp focus.

A more distant subject and less powerful lens has given this image deeper DoF. The front of the building and the distant clouds are both in sharp focus.

3. Relative Distance

If you are closer to your subject than it is to it’s background, you will be able to separate it from the background more easily. If the subject is close to it’s background (i.E. nearly on the same plane of focus), then separating it from the background, even with a very wide aperture, will be harder.

The two images above were taken using the same lens settings (f2.8, 40mm) and the same shooting distance. In the right image the second camera was moved back to show the effect of increasing the relative distance of the subject to their background and how it strengthens subject separation. The photographer to subject distance is now shorter than the distance between the subject and the rear camera.

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4. Controlling the Perception of DoF using Lens Perspective

The last way of controlling the perception of DoF and separation (but not actual DoF) is by using different lens perspectives. Wide angle lenses expand perspective, increasing the perceived distances between objects. Longer lenses compress perspective seemingly “squashing” things together. This is not actually changing DoF, only the perception of it.

Portrait photographers use the compression of longer lenses to make their subject jump out. landscape photographers often use the wider angle lenses to increase the perception of deep depth of field.

If an object photographed to be the same size in any two images, taken on any lens and any format camera but using the same aperture, the DoF is basically the same (the math is not exact, but basically holds true). The perception of separation is however very different.


In the two images above, the same aperture was used (f5.6) and the same focussing point. Every effort was made to keep the main subject the same size in the view finder by moving in closer with the wide angle lens. The left Image was taken at 40mm and the right at 12mm. Even though the left image is more compressed, increasing the perception of shallower DoF and better subject separation (also changing how the blurring looks), the actual DoF is about the same. It is just stretched out, making the transition less obvious.

For this image, a medium long lens (75mm) and very wide (f1.8) aperture were used. The distance to the focus point was about 3 meters and there is about a meter between each row of poles. The actual sharp DoF is about 2-3cm and the transition is minimal. This image is magnified by a close shooting distance and  compressed   and a longer than standard lens focal length.  It would be technically possible to create exactly the same effective DoF using a different focal length lens (as long as the magnification is kept the same by moving closer or further away), but the perspective and the relative distance to the background would change, making the poles look more or less "flattened".

For this image, a medium long lens (75mm) and very wide (f1.8) aperture were used. The distance to the focus point was about 3 meters and there is about a meter between each row of poles. The actual sharp DoF is about 2-3cm and the transition is minimal. This image is magnified by a close shooting distance and compressed and a longer than standard lens focal length. It would be technically possible to create exactly the same effective DoF using a different focal length lens (as long as the magnification is kept the same by moving closer or further away), but the perspective and the relative distance to the background would change, making the poles look more or less "flattened".

By contrast, this image used a wider lens, and a smaller f5.6 aperture from a similar distance. The wider lens decreased   the   magnification and  expands  the perspective, to help increase perceived DoF. These poles were actually closer together than the ones in the image above, but look further away.

By contrast, this image used a wider lens, and a smaller f5.6 aperture from a similar distance. The wider lens decreased the magnification and expands the perspective, to help increase perceived DoF. These poles were actually closer together than the ones in the image above, but look further away.

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As you have probably already worked out, most photographic situations will be a compromise of all of the techniques discussed above.

This image was taken with a slightly  wide  focal length lens (  decreased magnification  ), but at  close  distance (  increased magnification  ) and with a reasonably  wide f2.8 aperture  (  decreased DoF  ). The overall effect is of fairly shallow DoF due mainly to the short focussing distance and wide aperture being the strongest pair of elements.  In images such as this the quality of transition (Bokeh) becomes important.

This image was taken with a slightly wide focal length lens (decreased magnification), but at close distance (increased magnification) and with a reasonably wide f2.8 aperture (decreased DoF). The overall effect is of fairly shallow DoF due mainly to the short focussing distance and wide aperture being the strongest pair of elements. In images such as this the quality of transition (Bokeh) becomes important.

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In a nutshell;

  • For the most dramatic shallow DoF looks, use a wide (small number) aperture value and increase magnification by using a long lens and/or getting very close, especially if this exaggerates the distance from subject to it’s background.

  • For the strongest deep DoF effect, use wider angle lenses and small (large number) aperture values and don't get too close to the main subject relative to it’s background.

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Astro Photography

The rules we looked at above can be applied to great effect on astronomical photography.

Because the stars are so far away, it is possible to use a very wide aperture setting and still get everything in focus. This is really handy because time is your enemy with astro images. The more time you give the image, the better the colour and depth in the image, but because of the earth's rotation, (depending on the lens used- the wider the better), you will have from 1 to 30 seconds before movement blur ruins the image, unless you are after deliberately blurred star-trails that is.

The only things to keep in mind is the extra DoF needed to include foreground or earth bound elements in the image and possible lens aberrations* that appear when the widest apertures are used. Wider lenses are usually used as they give you more time, because they "push" things further away.

*Lenses used at their very widest apertures tend to show softness in the corners and chromatic aberration (colour fringing) or coma (smears) which may be obvious in your images. The newest batch of lenses are highly corrected, but older lenses will often show these flaws to some extent.  

Close-up Photography

The opposite is true for close-up photography. When you get into the macro (technically this is images that are reproduced in "life size"* or smaller, DoF drops off severely in response to the strong magnification and very small relative distances used. At focussing distances of only a few cm, even f22 will only give you a few mm of DoF. There are a few tricks you can use to increase DoF discussed in Tips and Tricks below. 

*Life size means reproducing the subject on the sensor the same size as it actually is, so a 1" camera sensor would cover 1" of actual subject.

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Tips and Tricks

1. Something you can do to increase useful DoF is to change the angle by "tilting" the lens/camera forward,  or downward (using vertical-portrait orientation helps) or sideways (along a fence line or wall) to match the angle of the focussing plane to the subject better. 

This is especially useful when you are placing a small subject like the head of a flower in the foreground and still want the distant horizon sharp or you are photographing a group of objects on one plane such as a table top, fence line or field of flowers. Some photographers use "Tilt/Shift" lenses to allow them to change the focal plane without moving the camera.

This image was taken with the same lens and at the same distance as the above images using f1.8 aperture,. It has both a wide aperture and close focussing distance severely reducing DoF. By placing all of the statues on the  same focus plane  (i.e. directly flat on to the camera), even a wide aperture can get (most) of them in focus (but nothing in front or behind). Shooting length-ways down a subject exaggerates shallow DoF effects, "tilting" to get closer to the same plane of focus reduces that effect.

This image was taken with the same lens and at the same distance as the above images using f1.8 aperture,. It has both a wide aperture and close focussing distance severely reducing DoF. By placing all of the statues on the same focus plane (i.e. directly flat on to the camera), even a wide aperture can get (most) of them in focus (but nothing in front or behind). Shooting length-ways down a subject exaggerates shallow DoF effects, "tilting" to get closer to the same plane of focus reduces that effect.

2. Another trick is to take multiple images at different focussing points and combine them in post processing or in camera with some models. This is called “Focus Stacking”, but it only works if your subject and camera stay still. Just like panoramic style images, the programme or camera used can only "stitch" the images together if they all match in framing.

3. For maximum possible DoF you can work out the "Hyper-focal Distance" focussing point. This can be done by  using either the lens markings if there are any (increasingly rare) or there are Apps available. This will tell you the best distance to focus at each aperture to guarantee the most DoF for your lens focal length and camera format. 

4. If you are finding it hard to achieve good DoF and quality in poor light or when doing close ups, use a tripod and/or flash. These will allow you to use f11-32 in combination with low ISO settings without slower shutter speed blur. Macro is also a good time to apply the tilting method to shoot side on or above your subject.

Lens Aberrations

If f16 or smaller are used, be aware that they will be limited in sharpness by “diffraction”. Diffraction occurs around the edge of any hole light passes through, bending light waves and degrading the quality of that light. As the aperture gets smaller and smaller, diffraction becomes dominant, until eventually most of the light is degraded (diffracted). Extremely good lenses are sometimes called "Diffraction limited" lenses , meaning the only optical flaw they have is the only one that cannot be avoided.

When a “fast” or very wide aperture lens is at it’s widest settings, there may be some form of image flaw visible such as chromatic aberration (colour fringing- often green or purple and most obvious in high contrast images) or corner softness. Only the very best lenses avoid these issues (see "Diffraction limited" above). 

A word on Bokeh

The transition from sharp to soft areas is often referred to as “Bokeh” (Bo as in bone - Ke as in kettle, the H is there to help with pronunciation, not that it always helps!) or more correctly Boke-Aji which is literally "the flavour or character of blur".

There is no such thing as good or bad Bokeh (although everyone has personal preferences). Every lens will render the out of focus and transitional areas of an image differently, some lenses even varying at different focal lengths and distances. Zoom lenses can be complicated here as they can vary with every focal length.

Some lenses have messy or busy Bokeh, some feathery or smeary, others smooth and blotchy (there are more "official" terms like Ni-Sen or cross-eyed Bokeh, but these more general terms get the point across and you do not need to learn Japanese). Some lenses have more coherent transition to out of focus areas and others, often modern designs, drop off smoothly and quickly for better portrait applications. Get to know your lenses Bokeh characteristics as they can be as important as sharpness when used often. 

The Bokeh in this image is smooth enough to be reasonably un-distracting. This allows the photo to be made up is mostly out of out of focus elements, adding creative options. Using another lens may change the character of the image for better or for worse. The nose of the pony is a little "nervous" or busy looking compared to other lens renderings, but is pleasant enough.

The Bokeh in this image is smooth enough to be reasonably un-distracting. This allows the photo to be made up is mostly out of out of focus elements, adding creative options. Using another lens may change the character of the image for better or for worse. The nose of the pony is a little "nervous" or busy looking compared to other lens renderings, but is pleasant enough.

Taken on the same day, with the same lens, this image again relies heavily on the quality of it's Bokeh. If the Bokeh was too messy looking it would distract from the point of the image and make the sharp point of focus less clear and important in image. Again this is slightly "nervous" looking Bokeh, but the long focal length and shallow DoF has separated the focussing point clearly.

Taken on the same day, with the same lens, this image again relies heavily on the quality of it's Bokeh. If the Bokeh was too messy looking it would distract from the point of the image and make the sharp point of focus less clear and important in image. Again this is slightly "nervous" looking Bokeh, but the long focal length and shallow DoF has separated the focussing point clearly.

Another example of Bokeh being an important element in a shallow DoF image. Poor Bokeh can effect the strength of an image. The only way to really know is to try out your lenses and compare their effects. If it feels/looks right, then go with it.

Another example of Bokeh being an important element in a shallow DoF image. Poor Bokeh can effect the strength of an image. The only way to really know is to try out your lenses and compare their effects. If it feels/looks right, then go with it.

Sometimes, la less fast drop-off Bokeh is desired. The lens that took this image as focussed (by mistake) at 2 meters and f2 aperture was selected (you can see the point of best focus is the first poster). The Bokeh characteristic of the lens was a more old fashioned "long transition" or coherent Bokeh, not as popular as the smooth and fast drop-of of most modern lenses, but very useful when the focus misses or DoF is limited. The people in the background are still clearly formed even though they are well out of focus and the   transition   from fully sharp to out of focus is almost invisible. Other lenses in the same situation (like the one used for the image above) may tend to make anything past the point of focus quickly look blobby or smeared and make this image pointless.

Sometimes, la less fast drop-off Bokeh is desired. The lens that took this image as focussed (by mistake) at 2 meters and f2 aperture was selected (you can see the point of best focus is the first poster). The Bokeh characteristic of the lens was a more old fashioned "long transition" or coherent Bokeh, not as popular as the smooth and fast drop-of of most modern lenses, but very useful when the focus misses or DoF is limited. The people in the background are still clearly formed even though they are well out of focus and the transition from fully sharp to out of focus is almost invisible. Other lenses in the same situation (like the one used for the image above) may tend to make anything past the point of focus quickly look blobby or smeared and make this image pointless.