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What is exposure in photography?

Digital Cameras Discussion

What is exposure in photography?

Postby collin95 » Sat Apr 20, 2013 4:14 am

Can someone give me a detailed explination on exposure, what it is and the exposure triangle etc. thanks in advance.
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What is exposure in photography?

Postby renke63 » Sat Apr 20, 2013 4:24 am

The exposure triangle has the Shutter, Aperture and ISO. In photography you must always balance these three things.

The shutter controls how long light falls onto the digital camera sensor. The aperture controls the brightness of the light that reaches the sensor. The combination of a particular aperture and shutter speed combination is referred to as an exposure.

Images can be overexposed. Overexposure means either the camera’s digital sensor was exposed to light for too long, or the aperture was too large and the light falling on the digital sensor was too bright.

Images can be underexposed. This means either the shutter speed was too fast and the camera’s digital sensor was not exposed to light long enough, or the aperture was too small and the light falling on the digital sensor was too dim.

Imagine a bucket of water and nozzle that fills it. The shutter is a timer for how long to fill the bucket and the nozzle size represents the aperture that can be changed. If the bucket needs filled, a large nozzle can be used to fill it in a short time, or a smaller nozzle can be used even though it requires more time to fill the bucket.

If the bucket can be filled in 1 second while the largest nozzle is used, when the nozzle is closed halfway, it would take 2 seconds. Regardless of the amount of time required to fill the bucket, it will hold the same amount of water. Exposures work the same way.

A photographer could open the aperture to its widest setting so it lets in as much light as possible. This would allow a faster shutter speed to be used. What if this setting only allowed a maximum shutter speed of 1 second but it needed to be faster in order to freeze motion?

In these situations, the camera’s digital sensor can be adjusted to increase its sensitivity to light. The amount of sensitivity to light is referred to as the ISO.

Using higher ISO levels means a faster shutter speed or smaller aperture can be used.

(However higher ISO levels introduce both noise, the colors no longer look accurate; the shadow contrast no longer appears natural. It is a good practice to use lower ISO levels when possible.)

Have a look at these
Exposure triangle
http://digital-photography-school.com/learning-exposure-in-digital-photography
https://www.youtube.com/watch?v=KQw28-3LEU4

Understanding stops
http://www.adorama.com/alc/0012643/article/Understanding-Stops-AdoramaTV

Aperture
http://www.adorama.com/alc/0012559/article/Aperture-Values-Adorama-Photography-TV

Shutter
http://www.adorama.com/alc/0012834/article/Slow-Shutter-Magic-AdoramaTV
http://www.adorama.com/alc/0012594/article/Freezing-Motion-with-Shutter-AdoramaTV
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What is exposure in photography?

Postby nell » Sat Apr 20, 2013 4:31 am

Exposure is the amount of light entering the sensor or film; wich depends on the area of the lens aperture and the time you let it comes in; any film or sensor has a sensitivity to light (first fix, second variable), wich makes that the same amount of light sensitizes it differently. And that's the famous triangle
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What is exposure in photography?

Postby farnly » Sat Apr 20, 2013 4:37 am

To understand exposure you need to learn the Exposure Triangle.
http://digital-photography-school.com/learning-exposure-in-digital-photography

ISO is simply a measurement of the sensitivity to light of a light sensitive surface, either film or digital sensor. The lower the ISO number the less sensitive and the higher the ISO number the more sensitive.

Aperture is the opening of the lens formed by the movable blades of the diaphragm. Its an inverse relationship - the smaller the f-stop number the larger the opening and the bigger the f-stop number the smaller the opening. So f1.4 is very large while f16 is very small. It controls how much light is admitted by the lens.

The shutter speed determines how long the light admitted by the lens is allowed to expose our film or sensor based on the ISO set. Shutter speed also determines if a moving object will be blurred or sharp.

Example:
f16 used with ISO 100 will give a slower shutter speed than f16 used with ISO 400. Suppose you're using f16 and ISO 100 and your shutter speed is 1/125 sec. Change to ISO 400 and at f16 your shutter speed will be 1/500 sec. If its a windy day or there is someone or something moving in your scene and you want to use f16 then to avoid motion blur caused by movement you'd need to use ISO 400. Conversely, suppose you don't want to use an ISO higher than 100 but you need a shutter speed of 1/500 sec. Here you'd "open up" your lens to f8. In both examples we added two full stops to either our ISO or aperture to achieve a two stop increase in our shutter speed.

Over exposure or under exposure is simply a product of using the wrong combination of f-stop and shutter speed at a given ISO. Suppose we're using ISO 100 and shooting in Manual and ignore what the camera's light meter tells us.

Instead, we decide to use f16 and a 1/500 sec. shutter speed. Our picture will be underexposed
because the little amount of light admitted at f16 wasn't allowed to expose our film or sensor for a long enough time to give a correct exposure. (Remember in our previous example ISO 100 and f16 needed a 1/125 sec. shutter speed)

Or, still ignoring our light meter but still using ISO 100, we decide to use f8 at 1/125 sec. Now our picture will be overexposed because the 1/125 sec. shutter speed allowed the light admitted at f16 to expose our film or sensor for too long. (Remember in our previous example ISO 100 and f8 needed a 1/500 sec. shutter speed)
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What is exposure in photography?

Postby quinn » Sat Apr 20, 2013 4:38 am

To understand exposure you need to learn the Exposure Triangle.
http://digital-photography-school.com/learning-exposure-in-digital-photography

ISO is simply a measurement of the sensitivity to light of a light sensitive surface, either film or digital sensor. The lower the ISO number the less sensitive and the higher the ISO number the more sensitive.

Aperture is the opening of the lens formed by the movable blades of the diaphragm. Its an inverse relationship - the smaller the f-stop number the larger the opening and the bigger the f-stop number the smaller the opening. So f1.4 is very large while f16 is very small. It controls how much light is admitted by the lens.

The shutter speed determines how long the light admitted by the lens is allowed to expose our film or sensor based on the ISO set. Shutter speed also determines if a moving object will be blurred or sharp.

Example:
f16 used with ISO 100 will give a slower shutter speed than f16 used with ISO 400. Suppose you're using f16 and ISO 100 and your shutter speed is 1/125 sec. Change to ISO 400 and at f16 your shutter speed will be 1/500 sec. If its a windy day or there is someone or something moving in your scene and you want to use f16 then to avoid motion blur caused by movement you'd need to use ISO 400. Conversely, suppose you don't want to use an ISO higher than 100 but you need a shutter speed of 1/500 sec. Here you'd "open up" your lens to f8. In both examples we added two full stops to either our ISO or aperture to achieve a two stop increase in our shutter speed.

Over exposure or under exposure is simply a product of using the wrong combination of f-stop and shutter speed at a given ISO. Suppose we're using ISO 100 and shooting in Manual and ignore what the camera's light meter tells us.

Instead, we decide to use f16 and a 1/500 sec. shutter speed. Our picture will be underexposed
because the little amount of light admitted at f16 wasn't allowed to expose our film or sensor for a long enough time to give a correct exposure. (Remember in our previous example ISO 100 and f16 needed a 1/125 sec. shutter speed)

Or, still ignoring our light meter but still using ISO 100, we decide to use f8 at 1/125 sec. Now our picture will be overexposed because the 1/125 sec. shutter speed allowed the light admitted at f16 to expose our film or sensor for too long. (Remember in our previous example ISO 100 and f8 needed a 1/500 sec. shutter speed)
It's a setting that allows you to change how much light the camera picks up which determines the brightness of the picture.
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What is exposure in photography?

Postby jai » Sat Apr 20, 2013 4:53 am

Exposure is basically how much light you allow into the camera depending on the shutter speed.
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