Friday, August 19, 2011

Trying to explain Shutter Speed!


Now that we’ve understood aperture and what it controls, its time to understand the second aspect of the photographic triangle. Its known as “Shutter Speed”. Its defined as the duration for which the camera’s shutter stays open.

Along with the aperture, the shutter speed determines how much light reaches the image sensor. The longer the shutter stays open, the more light can get inside the camera to make the exposure.

Shutter speed being a measure of time, its values are expressed in seconds…or, most cases in microseconds. For example, values like  1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15 and such. These values shows the fraction of a second that the shutter stays open. The bigger the denominator the faster is the shutter speed. And, if you notice, with every change of the shutter speed, the light entering the camera is either doubled or halved

(It’s the same in case of the aperture too! That with every stop down of the aperture, the area of the hole that opens, halves.  Its just not as obvious as the shutter speed and beyond the scope of this blog to explain the math behind that!)

Since, the amount of light that one would need to make a perfect exposure is fixed, it means…any changes in aperture will have to be compensated with a corresponding change to the shutter speed (considering we are not changing the ISO value!) , for the same exposure.

Say, you are able to get a perfect exposure at

aperture = f/5.6

shutter speed = 1/125

ISO = 400

Now lets decrease the depth of field in the picture, say, we want to drop down the, f/2.8.

That would mean, moving the f-number by 4 stops…

f/5.6, f/4.8, f/4, f/3.3, f/2.8

To not change the exposure, we would have to make a corresponding change to the shutter speed by raising the shutter speed by 4 stops.  That would be

1/125, 1/250, 1/500, 1/1000, 1/2000

So, to get the same exposure with a shallow depth of field, The values will now have to be

aperture = f/2.8

shutter speed = 1/2000

ISO = 400

Keeping this in mind, you wonder, if the exposure needs to be the same…why would one want to change shutter speed?! Lots of reasons..

You can use low shutter speed to show the effect of moving objects in your pictures..  You can use high shutter speed to freeze an action. For the picture below..when P was jumping on her trampoline..a shutter speed of 1/500 sufficed at f/2.8, ISO 200 to catch her in action.

_DSC7555 as Smart Object-1_DSC7580 as Smart Object-1

You would slow down the shutter speed if you want to show some motion blur in your picture.   Blur is not always bad… Sometimes, it can be used creatively, to show motion in your picture.  Almost like a still video, as paradoxical as that sounds..For example…in the picture below, you can see that Hubby dear was trying to throw the rope up somewhere!!  You can almost see the rope flying up. Isn’t it?


Or in here, that K was trying to lift a box of cheerios! The exposure values for this was  f/2.8, shutter speed of 1/6 sec and ISO of 200.


When a slower shutter speed is selected, a longer time passes from the moment the shutter opens till the moment it closes. More time is available for movement in the subject to be recorded by the camera.

Now that we know, slow shutter speeds cause blurs, what is the minimum shutter speed that one could use to have a picture taken so, there’s no blur?

If you are hand holding your camera, ( and considering you have a static subject! ) most photographic pros consider having a minimum of 1/60  shutter speed.   (That should roughly be about the focal length of a 50mm lens, for a full frame sensor.)

Some cameras give you the ability for very slow shutter speeds also. For example, 1”, 10”, 30”…measured in seconds. Why would you needs such shutter speeds? Suppose you want to take a shot of a night scenario. This calls for very long shutter speeds, measured in seconds..For eg.


This image was exposed , for 30 seconds at f/16 and ISO of 200.  (You can see..there’s still,  a slight blur in this image..caused by the action of clicking the pic itself…To get tack sharp the pros call them..they suggest using remote release cables or wireless shutter release or just plain self timer to release the shutter ).

To click such images,  you would first fix your camera, to a TRIPOD, then,  set your shutter speed to a value that gives you the best shot and click, considering that you have moved your mode dial on the camera to Shutter prority mode, or, the “S” mode!

You can use low shutter speeds to picture night skies, where you want to show how the stars move over a period of time. You can use it to show light painting, by making patterns with sparklers as you hold them. You can use it to picture streets at nights.

The picture below shows a light trail of a vehicle that was passing by my tent at a camp ground. You could use such shots to creatively picture city night. The light trails left by passing vehicles leave beautiful patterns.


There is another use of slow shutter speeds. Do you remember seeing posters of water falls were the water fall looks so silky smooth. This is achieved by using low shutter speeds too. One would need to use special filters to achieve these effects like neutral density filters. They cut the amount of light reaching the camera..allowing the photographer to use a very low shutter speed even during the day!…Here’s my experiment, I did at my kitchen sink!!! Which obviously shows..that I wasn’t thinking much in terms of being creative !

_DSC7758 as Smart Object-1  _DSC7759 as Smart Object-1

See, how the flow of water is softer in the second pic. Its because I had used a neutral density filter (0.6) on the lens..which required a longer exposure compared to the exposure of the first pic, thereby making the flow of water look softer.

Now that you know some things you could do by controlling shutter speed. Don’t forget to turn the mode dial on your camera to “S” and try out some shots that you had just been wondering how to!

You know, after writing all this…I come across this clip from Calvin and Hobbes and I thought it was worth mentioning for all that effort

Calvin: As far as I'm concerned, if something is so complicated that you can't explain it in 10 seconds, then it's probably not worth knowing anyway.

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