Photography Basics: Understanding Aperture, Shutter Speed and ISO
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Sunday, July 05, 2015
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Photography Basics - Understanding Exposure (Aperture, Shutter Speed & ISO)

To understand the basics of photography you must understand exposure.  There are 3 basic elements that affect the exposure of an image:  

  • Aperture
  • Shutter Speed
  • ISO  

When you see a well lit image the camera has captured the right amount of light required to expose it properly. The correct exposure is made from a proper balance of aperture, shutter speed and ISO.  To get a perfect exposure and get the image to look the way you want you must understand how to balance these 3 elements.  I will try to break each element down into simple terms.


What is Aperture?

Aperture is the circular opening in your lens that you make larger or smaller to let in more or less light.  The aperture settings for the lens are called f-stops.  The f-stop is basically the size of the opening of your lens.  If you look at your lens when you change the aperture setting you can see the blades.  Changing the aperture value will change the size of the opening made by these blades.  The amount of light being let in is determined by the f-stop value (aperture value).  The ironic part is the smaller the f-stop number (f2.8) the more light it will let in and the arger the f-stop number (f22) the less light it will let in.  



F-Stops Aperture

Aperture also impacts the depth of field in your image.  Depth of field is how blurry the foreground or background of your image is compared to the subject you are focusing on or basically how much of your image is in focus. Shallow depth of field is when your subject is in focus but the background or foreground is out of focus.  


If you use a large lens opening (f/2.8) when your subject is in focus the background will be very blurry.  

depth of field comparison f2.8


If you use a smaller opening (f/22) the background will be less blurry.  

depth of field comparison f22


What is Shutter Speed?

The cameras shutter speed controls how long the sensor is exposed to light.  The amount of time the shutter is open will determine the amount of light that gets through to the sensor.  The faster the shutter speed the less light you will let in and the less amount of time it has to make the image.  The slower the shutter speed the longer it takes to make the exposure and you will be letting more light create your image.  Because shutter speed is just that, speed of the shutter, opening and closing it also controls the amount of movement (or blur) in your image.  


The faster your shutter opens and closes (1/500 of a sec or faster) means you will have less time for things to move around and look blurry.  


If the exposure takes place for a longer amount of time meaning you have a slow shutter speed (1/30th of a sec or more) more light will be let in and there will be more time for the subject to move and become blurred.   



What is ISO?

ISO is the sensitivity of the image sensor in the camera.  ISO controls how much light the sensor needs to make the image. The higher the ISO the more sensitive the sensor is to light meaning you will need less light to expose your image.  The lower the ISO the less sensitive it is to light meaning you will need more light to expose your image.  

If there is bright sun you can use a lower ISO.  When there isn't much light you may need to raise your ISO. There is a tradeoff of with ISO to be aware of.  The higher the ISO the more grain or noise you will get in your image.  

Photography Basics Summary:

To summarize there are 3 basic elements to photography:

  • Aperture
  • Shutter Speed
  • ISO

Aperture affects the amount of light that comes into the sensor and the depth of field.  The depth of field will determine how much of the image is in focus.  Shutter speed will determine the length of the exposure and the amount of motion blur that willl appear in the photo.  The longer the shutter speed, the more light comes in, and the shorter the shutter speed the less light will come in.  And finally ISO is the sensitivity of the sensor to light.  Lower ISO mean the sensor is less sensitive and therefore going to need more light to expose an image.  Higher ISO requires less light to expose an image but adds noise.


Getting the perfect exposure is all about balancing these 3 elements.  It might take some time but if you understand these basic concepts it will get easier with time.   


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