05.03.2013

Understanding Exposure by Jacob James

05.03.2013

Understanding Exposure by Jacob James

UK local hero Jacob James is a young and talented travel photographer currently studying at Leeds University who will be sharing with you a series of 8 weekly articles covering in an informal way an Introduction to Photography – in this second in the series Jacob looks at some easy tips to help you Understand more about Exposure, a key area to taking better photos!

Exposure is one of the key principles in producing an image. Many cameras will have an ‘auto’ mode which deals with the exposure automatically but having a basic understanding of exposure is essential if you wish to ditch the full auto mode on your camera and give yourself some extra creative control. Exposure is controlled by three elements; Lens aperture, shutter speed and ISO. Exposure can be explained using the simple metaphor of a tap and a bucket.

Aperture – The lens aperture is the means by which the camera controls how much light hits the sensor. You can think of the aperture in the same way as you would the width of a tap. The more wide open the aperture (smaller f-number) the more light hits the sensor, or in the case of the tap, the wider the tap the more water falls into the bucket. Aperture also controls depth of field (the amount of in-focus areas in an image) and the wider the aperture the shallower the depth of field. This can be a disadvantage in low light as you may find it hard to get a low enough aperture (big f-number) to get everything sharp in the image.

Shutter Speed -The shutter speed is the amount of time the sensor is exposed to the light. You can think of the shutter speed as the time you have the tap open. The longer the shutter speed, the more light hits the sensor. The longer you leave the tap open the more water will fall into the bucket. The only caveat with shutter speed is that, as a general rule, if the shutter speed is not greater than the reciprocal of your focal length you will see the appearance of camera shake (For instance 50mm = 1/50s).

ISO – The final part of the exposure triangle is ISO. You can think about ISO as the rate of water running through the tap. The higher the ISO the more sensitive the sensor is to light. Using the metaphor of the tap again, if the water is flowing at a higher rate, more water will fill the bucket. Therefore low light is like having a huge bucket; you need a much faster water rate (higher ISO) to fill it. The downside to high ISO is that it increases the appearance of noise (grain) in the image. This is the reason why images taken on phone cameras or small compact cameras will appear grainy if taken in low light situations.

As you can see with the tap and bucket metaphor, if you decrease an attribute such as the width of the tap, you will have to increase another such as the time the tap is open if you wish to fill the bucket. Exposure on a camera works exactly the same, if you decrease the aperture (bigger f-number) you have to increase the shutter speed to counteract this change. Understanding the relationship between the three key components may seem very complex but a solid understanding of exposure will reap you with more creative ability than ever before.

Please post your feedback, questions and views on this article or related topics and we will do our very best to answer them for you!

Look out for Jacob’s next article in the 8-part series: ‘Great landscape images: Learning composition’.

For more information visit Jacob’s blog at: http://jacobjamesphotography.co.uk or Twitter: @JacobJamesPhoto

 

 

 

 

 

 

 

 

 

 

 

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