Previously it was stated that there are three important variables
for setting exposure in photography, namely, aperture, shutter-speed and ISO.
Shutter-speed is one of those three variables to control the overall
exposure of a photograph.
In front of the film or digital sensor of
a camera, there remains a pair of curtains
(named as front curtain & rare curtain)
which blocks any light to reach
the film or sensor. In general, when we are in front of
a scenario to photograph,
we first set the composition, framing, focal-length, focus-point,
aperture, shutter-speed, iso, white-balance etc. When everything is
fixed, we press the shutter-release button which is the final step for
recording a photograph.
When we finally press the shutter-release button, one of the
curtains folds itself, and allows
light to reach the film or sensor through the lens.
We skipped a mirror-mechanism in case of DSLRs,
which will be discussed in
shutter mechanism page.
The curtain remains
folded for a moment, say for 1⁄500th. of a second, or for ½ or 2 seconds
(whatever period we set it earlier). During this
period, the film or sensor remains exposed to light, and
an image is recorded in digital format.
This time period, for which the film or sensor remains open to light,
is called shutter-speed
of that particular photograph.
The unit of shutter-speed is the unit of time; and may be
expressed in seconds, minutes, even in hours.
Imagine yourself inside a very dark room where all the doors
and windows are closed. There is day-light present outside
the room, but no light inside. Now you open a window
just for 1 second, then close it. The room will be exposed
to light for 1 second. This time period of 1 second may be
called as shutter-speed; and the size of the window may roughy be
referred to aperture of a lens.
Different shutter-speeds effect on
1 - exposure of an image
2 - motion of moving elements
next page.
Effects of Shutter-speed on Exposure
The overall exposure or brightness of a photograph
varies with different shutter-speeds.
Faster the shutter-speed, darker the image,
and slower the shutter-speed, brighter the image,
other variables remaining constant.
When the film or sensor remains open for a very less period
of time, say for fraction of a second, less light enters the film or sensor, and the image
recorded during this period tends to become dark. Such
shutter-speeds are called
fast shutter-speed.
Examples of fast shutter-speed are
1⁄500th.
sec., 1⁄2000th. sec. etc.
If situation compels you to use a very fast shutter-speed,
say to capture a bird in flight, you must compensate light
with higher ISO or wider aperture.
An example of freeze-motion effect with fast-shutter,
f/7.1, 1/4000 sec., ISO 640, 24mm eqv. Varanasi, India 2015
Nikon d810, Tamron 24-70mm f/2.8
Above is an example of fast-shutter (1⁄4000sec.) which freezes
motion, and tends to darken the photograph.
On the other hand, when the film or sensor remains open
for a longer period of time, say
½ or 1 second,
more light enters the film or sensor,
and the image recorded during this period tends to become very
bright. Such shutter-speeds are called
slow shutter-speed. Examples of slow
shutter-speed are
1⁄15, 1⁄10, 1, 2 sec...
When the film or sensor remains open for a very long period
of time, say for 30 sec., 1 minutes ..., we may call this as
long exposure.
While shooting long-exposure shots, we must take measures to
block the excessive light during this long period of time.
An example of motion-blur effect with slow-shutter,
f/4.5, 1/4 sec., ISO 200, 27mm eqv. Katigorah, India 2021,
Fuji x-t30, Fuji 18-55mm f/2.8 - 4
The above example uses a slow-shutter (1⁄4 sec.)
and some amount of motion-blur has been captured. Slow-shutter
also tends to allow excess light; the above image has been
darkened in post-processing purposefully.
Longer the shutter-curtains remain open, more amount
of light is allowed to the film/sensor, and the image
gets brighter. Shorter this period, less amount of light
is allowed, darker the image. The duration for which the
film/sensor receives light can be controlled by a switch
or from menu of a camera.
The following chart displays the effects
of various shutter-speeds and some of their applications.
We must remember
that those rules are not rigid, and shutter-speed should be chosen
as per the requirement in the field.
Long exposure: ... 1 min... 30 sec...▶
● Long-exposure of smoothing flow of water
● Car-light trails, astro photography
● Tripod is a must have
● Remote mechanism may have to be applied
● Lens VR/IS/OIS should be switched off
● Sensor may become hot
● ND filter may be required
● Hard in bright daylight
● Suitable in early morning, evening and night
● Use base ISO
Very slow-shutter: ... 1 sec... ½ sec...▶
● Good amount of light received
● Tripod is required
● Required in low-light situation
● Indoors, church, car-light trails, waterfalls
● Motion blur may creep in
● Hard in bright daylight
● Use low ISO
Slow-shutter: ... 1⁄10 sec... 1⁄20 sec...▶
● Good to medium amount of light received
● Suitable for stationary subject
● Tripod may be required
● Motion may be captured in artistic way
Medium shutter: ... 1⁄125... 1⁄250 sec...▶
● less amount of light received
● street photography, incidents, happenings
● Probability of motion-blur reduces
Fast shutter: ... 1⁄1000... 1⁄2000 sec...▶
● Very less amount of light received
● Birding, wildlife, sports
● ISO may have to be raised
● Aperture may have to be widened
Very fast shutter: 1⁄4000... 1⁄8000 sec...▶
● Very very less amount of light received
● Suitable for birding, wildlife, sports
● ISO may have to be raised
● Aperture may have to be widened
Simply, a fast shutter-speed allows less light, and a slow or long shuter-speed
allows more light. So, to control the incoming light, we set shutter-speed
through the wheels/buttons or the menu of a camera.
Please observe the above images. The settings of all the
three images were kept the same,
except shutter-speeds. They were ½, 0.8 and
1.6 seconds respectively. The first image (darkest) has a faster shutter-speed
than the second one, which has a faster shutter-speed than the
third one(brightest). Thus the brightness of each image varied according
to the different shutter-speeds applied.
Here is one more set where settings of all the
three images above are the same; f/11, and iso-64. But
shutter-speeds varied as 1⁄400, 1⁄200 and 1⁄100
seconds respectively (faster to slower). Faster shutter
darkened the image, while the slower one brightened it.
In case of the first image, because the sensor or film remained
open to light for a very small fraction of time(1⁄400 sec),
less light was allowed, and the image is the darkest in the series.
Note : It has been observed that a long focal-length
requires a faster shutter-speed to avoid recording of any camera-shake.
Generally, if you shoot a 300mm shot, set your shutter-speed 1⁄300 sec. or faster.
HDR : High Dynamic Range (Exposure Bracketing)
Why should we shoot the same scenario with different brightness?
When a scenario consists of both sky(with bright light) and ground elements, we find
the sky to be brighter than the ground. This difference of brightness
is most if we aim the camera towards the Sun or a bright light-source.
Such a scenario may be referred to as high-contrast scenes.
If we meter the exposure
from a part of the sky, the resultant image will properly expose the
sky, but the ground elements will be under-exposed. On the other hand,
if we meter from a part of the ground, the sky will be over-exposed,
and the ground will be properly exposed.
The capability of a camera sensor to keep both
the brightest and the darkest parts of a scenario properly exposed
(to some extent)
is known as the high dynamic range or HDR capability of that sensor.
Even if the HDR capability of a camera sensor is very less, we may still
get a properly exposed image from a high-contrast scenario by shooting
3 to 5 images with different brightness, and by post-processing them later.
Those type of images are known as
exposure-bracketed images. Modern cameras
have this feature, where you can shoot multiple images with different
brightness with a single click of the shutter. A tripod is very
helpful in such cases to keep the same frame in all the images.
There are also softwares dedicated to processing of HDR images.
They receive a set of bracketed images as input (with different exposures),
and produce a single properly exposed image out of the bracketed images. They can also
be manually processed to get the output as per personal taste.
Following is an example of a final HDR image generated from three exposure-bracketed
images having different exposures. Please use a tripod to keep same frame-alignment
for the input images.
Another example follows, where only two images were merged to produce the final
output. Actually, in this case, a single image was almost enough to present
without HDR merging,
but a slightly brighter-exposure was used additionally to get a bit of details
of the land areas.
An example of a (two) merged image,
Camera: Canon g7x mark ii,
Badarpurghat, Karimganj, Assam, India 2021.
We have seen how different shutter-speeds affect the exposure or
brightness of a photograph.
In this page,
we shall see how shutter-speed
freezes motion of a subject or records motion-blur in a photograph.
