The Effects of Changing the Shutter Speed

The shutter in the camera is a mechanism to limit the amount of light that reaches the sensor (or film).    This amount of light is directly proportional to the time the shutter is open – the shutter speed.     In low light conditions such as at night or indoors the shutter needs to be open for a longer time in order for sufficient light to reach the sensor.   Outside on a bright day the shutter needs to be open for only a very short time to capture that same amount of light.

In the early days of camera design when the photographic medium was very slow shutters were not necessary: the exposure was controlled by removing and replacing a lens cap or even shielding the front of the lens with a hat.  The exposure time was in the order of several seconds and a slight variation in this duration made little difference.

With the invention of film the medium became faster and any variation in exposure time resulted in huge differences to the picture.  Some form of mechanism was needed that could accurately expose the medium for very short periods and the durations of these needed to be consistent.      Any type of “guillotine” in which a single curtain slid open to expose the film and then slid back after a predetermined time had a huge disadvantage because the inertia in the stopping of the opening movement followed by  the subsequent reversal of direction took a finite time and thus prevented very short exposure times from being achieved.  I do not propose to go through the history of shutter development – there is a good article on this in Wikipedia – but will mention three. The Leaf Shutter; the Focal-Plane Shutter; and Electronic Shutters.

In the Leaf Shutter, when the shutter-release is pushed a set of five overlapping blades, arranged more-or-less like the aperture control mechanism of a lens and powered by a spring, begin to open.  When the exposure time is reached the blades close again.  From the commencement of opening to the final closure all the light coming through the shutter  hits every part of the film or sensor. Yet, as in the simple guillotine type mentioned above, this mechanism has to stop and reverse, thus the Leaf Shutter is not capable of allowing very short exposure times – typically 1/500 second and slower.  In addition, Leaf Shutters are typically placed within the lens which requires all other lenses to be used by that camera to have shutters as well.

The Focal-Plane Shutter sits immediately in front of the film or sensor within the camera body itself.  With this type of shutter protecting the medium the user is able to look through the lens at any time without exposing the film or sensor to the light.  In addition the choice of lenses one can use on the camera is much wider since there is no requirement for a lens to have its own shutter.  The Focal-Plane shutter has two screens or curtains, placed very close to each other, that both move in the same direction .  Before the shutter release is pushed the first screen is in its closed position and the second screen is open.  When the release is pushed, the first curtain begins to move across the medium opening up more and more of the image.    When the selected exposure time has passed from the start of the first curtain’s movement, the second curtain begins to move across in the same direction stopping any further light from reaching the medium.     Since these two curtains are independent much faster shutter speeds are possible.    But, since at fast shutter speeds the second curtain may start to close before the first curtain has completed its travel, not every part of the medium is exposed at the same time.  The image proceeds across the medium in a stripe.  This can in some instances cause distortion of objects that are moving relative to the camera, however this is a relatively rare phenomenon.

Now with modern cameras that use a sensor rather than film there is obviously no need for a mechanical shutter: an Electronic Shutter could be used.    But since the sensor is also the source of image for the viewfinder it cannot simply be powered on and off.    Instead, when the shutter release is pressed more power is sent to the sensor and the software captures the image.   Yet with increase in power to a sensor electronic noise is generated -- just as with increasing ISO levels.    So with current engineering cameras with electronic shutters tend to produce noisier images.


The Shutter – Controller of Movement

Varying the shutter speed on the camera enables the photographer to choose how the camera catches movement. When everything in the shot is still the shutter speed does not matter: the scene remains unchanged as time passes. However, when there is movement involved, the photographer needs to decide how to capture it. A fast shutter speed freezes the action – everything appears sharp; a slow shutter speed results in blurring. Which is chosen depends on a couple of factors: how much light is available and how the photographer wants to present it.

When plenty of light is available on the scene pretty much any shutter speed will work. However, the sensor (or film) requires a certain amount of light to faithfully capture the image and this amount is a fairly narrow band.   Too much light and the image is 'blown' or overexposed to a whitish color devoid of detail;   too little light and the image is darker or black, and again details are lost.   Thus to keep the captured light within these bounds requires the aperture to change to compensate for the speed. A faster shutter speed requires a larger aperture; a small aperture is used when the shutter speed is longer.    It is a delicate balance.

RIAT, UK, 07/15/2015<br />
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NonCommercial 4.0 International License

In WWII, during August of 1940 the Battle of Britain was raging in the skies over England.   During one of the many dogfights the Hurricane of Flight Lieutenant James Nicolson of 249 Squadron was badly damaged by fire from Luftwaffe aircraft.    As he was preparing to bail out of his burning aircraft, the burned Nicolson observed another German aircraft nearby.    Remaining with his stricken Hurricane he attacked and shot the German aircraft down.   This delay in bailing out has caused him to be more severely burned and when he finally reached the ground the Home Guard mistook him for a German pilot and shot him in the legs!

For his valor he was awarded the Victoria Cross.               

In 2015,, for the 75th Anniversary of the Battle of Britain, The Royal Air Force painted one of their Typhoon FGR4s (ZK349) in a Battle of Britain camouflage scheme  and adorned with the squadron markings GN-A -- the markings of Nicolson's Hurricane -- on either side of its  RAF roundel.     The GN-A markings earned it the affectionate nickname 'Gina'.

When I was at RIAT in 2015 there was going to be a flypast of this Typhoon with a WWII Spitfire 1A (EB-G).   A flypast with two very dissimilar aeroplanes with different maneuvering ability at low altitude and in a relatively confined space is extremely difficult.    In order to catch them both together from my vantage point I chose a shutter-speed of 1/1000 to freeze the moment and tracked the Typhoon during its approach.    When I saw the Spit in my viewfinder I pressed the trigger to get the shot above.    (Note how the fast shutter-speed 'freezes' the Spit's prop!)



In most cases using the fastest shutter-speed for the lighting conditions helps minimize blur from camera shake etc.    However, there are instances when depth of field requirements or artistic interpretations demand a slower shutter speed.    Thus the remainder of this tutorial and its accompanying photographs show the effect of changing the shutter speed when taking a photograph of a fast-moving object – in this case the flow of water, about 5,000 cubic feet of water per second at Morgan Falls Dam in Sandy Springs, GA. (Morgan Falls Dam) .

Morgan Falls Dam, Sandy Springs, GA, 12/29/2020,<br />
This work is licensed under a Creative Commons Attribution-<br />
NonCommercial 4.0 International License.
Morgan Falls Dam, Sandy Springs, GA, 12/29/2020,<br />
This work is licensed under a Creative Commons Attribution-<br />
NonCommercial 4.0 International License.

The fist photograph was shot at 1/4000 second. Notice the details of the flowing water are crisp. From here, slowing down the shutter speed results in relatively small loss of clarity until the shutter speed was 1/640 second. (For ease of viewing, only photographs pertaining to the text are shown. The complete set of photographs taken at speeds from 1/4000 second to 8 seconds can be viewed at Morgan Falls Photo Set).

Morgan Falls Dam, Sandy Springs, GA, 12/29/2020,<br />
This work is licensed under a Creative Commons Attribution-<br />
NonCommercial 4.0 International License.
Morgan Falls Dam, Sandy Springs, GA, 12/29/2020,<br />
This work is licensed under a Creative Commons Attribution-<br />
NonCommercial 4.0 International License.

As the shutter speed is slowed more and more light is allowed in since the shutter is open for longer. To compensate for this the aperture is continuously reduced to lessen that amount. Eventually the limit of aperture is reached, in the case of my Canon T6s Rebel that is f/32. To be able to continue slowing the shutter speed it is necessary to use a Neutral Density (ND) Filter reduce the light coming in. These two photographs were taken at 1/60 second at f/32 with no filter and f/4 with a ND64 filter. The ND64 drops the light coming in by six stops (f/32 -> f/4 = 6 stops).

Morgan Falls Dam, Sandy Springs, GA, 12/29/2020,<br />
This work is licensed under a Creative Commons Attribution-<br />
NonCommercial 4.0 International License.
Morgan Falls Dam, Sandy Springs, GA, 12/29/2020,<br />
This work is licensed under a Creative Commons Attribution-<br />
NonCommercial 4.0 International License.

As the shutter speed was increased so the water-flow became less and less detailed, more and more metaphysical. At 1.6 second shutter speed the appropriate aperture was again at f/32, so the ND64 filter was replaced by a ND1024 (10-stop) filter. The series concluded with a shutter-speed of 8 seconds with the ND1024.

This tutorial was designed to show the effect of lengthening the shutter-speed with a continuously moving subject. In looking through the photographs in the series, as the details of the water flow become less defined, less distinct, many people will say “That doesn’t look real!”

Yeah. That’s the point. This tutorial is demonstrating a tool that is available for the photographer to use. Remember, a photograph is a story. In some cases that story is non-fiction or, if you like, journalistic. It is saying ‘This is how it was.’ There is the minimum editing and that is confined mainly to adjusting the overall light slightly.

But in other cases (and for me, personally, this is much of the time) the story is more about ‘This is what I felt when I was there.’ Editing will be more expansive: cropping, removing pieces, cloning-in areas, lightening or darkening, sharpening and blurring. This is the photographer as artist – trying to let the viewer experience the feeling, the sense of the moment.

And shutter-speed is a major tool for doing this.

Morgan Falls Dam, Sandy Springs, GA, 12/29/2020,<br />
This work is licensed under a Creative Commons Attribution-<br />
NonCommercial 4.0 International License.
Alpharetta,    08/28/2017<br />
Going am Wilden Kaiser, Tyrol, Austria<br />
Shutter 1/12<br />
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NonCommercial 4.0 International License

For example, say I went to Morgan falls on a moonlit night.      The flowing water would still be the same, have the same ripples, same flying droplets, but in the pale light I would not have been able to discern them.    And likewise, in the ambient light I would need a very long exposure to capture the photo -- hence the 'streaming' appearance of the water.  

Another example of slow shutter-speed in full daylight could be when I want a long exposure to emphasize the speed of vehicles passing  by my picnic place.    I need the long exposure to capture the movement, but I might not be able to get a small enough aperture, so I would need an ND filter so that I can set the long exposure while keeping within my camera's aperture range.

Sources:

Caleb Ward (2016) How Do Camera Shutters Work? Retrieved from How Camera Shutters Work


Time-Life Books (1971)   Life Library of Photography - The Camera       USA: Time Inc.


The Aviationist  May 15, 2017   Special Colored RAF Typhoon FGR4 “GiNA”