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Exposure – Shutter Speed



Small WaterfallIn the last section we talked about Aperture and how we use it to control the amount of light and depth of field of our photos. 


Now we are going to look at Shutter Speed and how we use it to control how long the light hits the camera’s sensor or film.  These shutter speeds are in increments of time from 30 seconds to 1/8000 of a second. Most consumer level DSLRs and some advanced compacts top out at around 1/4000 of a second (still pretty fast huh?).  Another time setting that most cameras have is called BULB which lets you keep your shutter open for as long as the shutter is depressed.   Bulb exposures are usually  taken with a remote shutter release cord.

Maybe you have seen nighttime pictures of star trails.  These photos are taken on a tripod with the shutter open for very long periods of time using the bulb mode. These are generally taken out in the middle of nowhere (don’t want any light from cities), on very clear nights. If you are interested in trying this, take a picture while pointing your camera at the north star.  You will create interesting circular trails as everything spins around the north star.  See some great looking star trail photos here

Dropping DiceSo, how do you use the Shutter Priority (S or Tv) to produce creative photos.  Let’s use an example similar to the one in our discussion of aperture.  I am taking a photo of a waterfall in program mode. The camera’s meter tells me it is using the following settings:  Aperture of f4, Shutter Speed of 1/60sec. at an ISO of 200.  A shutter speed of 1/60 of a second is going to freeze the motion of the water, as it falls, more than we may want.  I need to slow my shutter speed to make the water look smooth and surreal. 

To do this we need to slow our shutter speed down considerably, to at least 1/2 second, maybe more, depending on the look we are after.  If I switch to Shutter priority (S or Tv) mode and change to 1/2 second what happens to my aperture?  That’s right, it needs to stop down from f4 to keep the amount of light hitting the sensor or film constant, based on the meter reading.  

Standard stops for shutter speed are in increments as follows:  1/1000 s, 1/500 s, 1/250 s, 1/125 s, 1/60 s, 1/30 s, 1/15 s, 1/8 s, 1/4 s,1/2 s and 1 second etc.  So to go from 1/60 sec to 1/2 second we need to decrease the light by five stops.   However, there is a problem, our lens only stops down to F22.  If we go from f4 to f8 to f11 to f16 to f22 it is only four stops and we need five.  But, if we look back at the original settings we see that the ISO is set to 200 so if we change it 100 we will get our fifth stop.


procession-11If the range you need to slow down the shutter speed is greater than what is available, through Aperture or ISO, you can add filters that cut the light further.  A circular polarizer will give you about 1 to 2 stops and neutral density filters can cut the light even further.  Neutral density filters can be purchased in different densities usually referred to in #X designations.  For example a 2X will cut 1 stop of light a 4X-2stops, etc. They can also be stacked to increase the density.


What if you are taking photos of something moving like a car, a plane,  a motorcycle or your child’s soccer game and would like to stop the action.  Well you need to increase your shutter speed, the setting will be totally dependent on how fast the subject is moving. 



In the example to the right of the F-18 fighter, I used 1/400 of a second to capture it in flight.  Of course when you increase the shutter speed you also need to open up the aperture to allow the exposure to remain constant.  If you open the lens up as wide open as it will go your only other control is the ISO setting.  P.S. There are no filters to add light to the equation so the trilogy is all you’ve got.



Beware of increasing your ISO too far as the photo will have more “noise” (little specks - kind of like individual grains).   The latest camera offerings are getting better and better at noise control, at the higher ISO settings, so you might get by with higher numbers.  I try to keep my cameras ISO setting below 1600, but then I don’t’ really like “noise” at all.  I guess you could call me “noise” snob.  The reason is that I don’t like the look of excessive post processing noise reduction.



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