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Depth of filed depends on
three
factors. It is inversely proportional to Lens focal length and aperture. It
is directly proportional to the distance between the camera and the subject.
If the focal length is more the depth of field is less. A telephoto lens has
less depth of field compared to a wide angle lens. If the aperture is open
the depth of field will be shallow as compared to a closed down aperture. It
is in fact a combination of all the three factors which influences the depth
of field.
If we are taking a picture with a telephoto lens (wildlife,
sports or fashion) we are starting off with a shallow depth of field as the
focal length is not in favour of DOF. To get more DOF we have to relatively
close down the aperture much more as compared to if we were shooting with a
wideangle lens ( landscape, reportage etc)
DOF is not equally distributed. It is more behind the subject than in
front of it. The DOF is the region where the size of the circle of
confusion is less than the resolution of the human eye. Circles with a
diameter less than the circle of confusion will appear to be in focus. |
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Less
depth of field |
More depth of field |
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1/500 sec at f/6.3 Center weighted |
1/80 sec at f/16 Center weighted |
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The bulb and wires
in the background in the second picture is also in focus (in comparison
to the bulb/wires in the first picture) but relatively less sharp than
the bananas. It is the point or plane that is focused in the camera has
maximum sharpness even if there is a lot of depth of field. It also
depends on the focal length of the lens used. The focal length of the
lens and distance are constant in both images.
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If we are taking a picture with a
telephoto lens (wildlife, sports or fashion) we are starting off with a
shallow depth of field as the focal length is not in favor of DOF. To get
more DOF we have to relatively close down the aperture much more as compared
to if we were shooting with a wide angle lens ( landscape, reportage etc) On
the other hand even though one may be using a wide angle lens but if the
aperture is quite open and the distance to the subject is also quite less,
the depth of field may be shallow unlike it should be in case of a wide
angle lens. |
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How to achieve
shallow depth of filed? |
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The best way to achieve a shallow
depth of field is to use a tele lens or a relatively longer focal length.
secondly fill up the subject as much as you can, i.e reduce the distance
between the lens and the subject or in other words be somewhere close to the
minimum focusing distance of your lens. Further keep the aperture as open as
possible keeping in mind the aperture-shutter speed exposure combination.
Keeping the aperture wide open may sometime lead to too shallow a depth of
filed that you may not get all portions of your subject covered within
the shallow depth of filed. This may be desired at times, which is why it
important to always focus on the eyes as the eyes are are the most important
area in a photograph and we cant afford to have them not in focus. To
counter this, you may arrange your subject in a manner so that there is
maximum possible difference between the subject and the background. Now you
may closed down the aperture a little bit more as the increase in depth of
filed will only influence the subject and not the background. |
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lens-long 200mm
(300mm on digital) |
lens-normal 50mm shot
on film. |
lens-wide 24mm (36mm
on digital) |
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distance-less |
distance-less |
distance-less |
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aperture-open |
aperture-open f1.8 |
aperture-open f6.3 |
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DOF= less |
DOF= less |
DOF= less |
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24mm
lens 1/20 sec at f/6.3, ISO 200, multi-pattern metering |
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| Although shot with a wide angle lens,
the background is out of focus because the aperture is wide open at 6.3 and
subject is very close to the camera. |
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As the focal length is increased
notice that the background is becoming less sharp. Depth of field decreases
as the focal length is increased. Also, if the focal length was kept the
same and the photographer moved closer to the subject, it can be concluded
that the depth of field decreases as the distance between the subject and
the camera decreases. Notice that as the camera is moved closer or as the
focal length is increased the background becomes more out of focus. There is
more blur in the last picture compared to the first. DOF is inversely
proportional to focal length and directly proportional to distance.
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Effective
depth of field for foreground |
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Depth of field is not just about the
background. we can sandwitch a sharply focused subject between a blured
foreground and background which effectively highlights the subject. Do
remmember that the depth of filed drops much faster in the foreground
compared to the background. Also at times the out of focus foreground
may look distracting so handle the technique with care. |
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 canon eos
40D 100mm F2.8 1/60th sec |
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 Nikon F801s
Illford.Telephoto lens |
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