EXPOSURE TRIANGLE

The three main elements that need to be considered when playing around with exposure by calling them ‘the exposure triangle’. 

Each of the three aspects of the triangle relate to light and how it enters and interacts with the camera. 

The three elements are: 

 

1. ISO – the measure of a digital camera sensor’s sensitivity to light 

2. Aperture – the size of the opening in the lens when a picture is taken 

3. Shutter Speed – the amount of time that the shutter is open 

 

It is at the intersection of these three elements that an image’s exposure is worked out. 

Most importantly – a change in one of the elements will impact the others. This means that you can never really isolate just one of the elements alone but always need to have the others in the back of your mind. 

Keep in mind that changing each element not only impacts the exposure of the image but each one also has an impact upon other aspects of it (ie changing aperture changes depth of field, changing ISO changes the graininess of a shot and changing shutter speed impacts how motion is captured). 

 

ISO.  This is your camera’s sensitivity to light.  The strength of light that rushes into a room in your house is very similar to the way your camera interacts with ISO.  

  

In traditional (film) photography ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking. 

 

In Digital Photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots.  

 

If you have lots of light, from either the sun shining BRIGHTLY or even if it’s overcast, but still real BRIGHT, you don’t need your ISO to aid your lighting much, so you can set your ISO low, like {100 or 200}.   If it’s totally overcast, ISO can help your camera absorb more light.  You’d want to set your ISO to a mid-range number like {400 or 800}.  And if the sun is setting and your light is fading, ISO can enhance your lighting if you set it high.  High ISO numbers are {1000 and higher}. 

  

100 ISO is generally accepted as ‘normal’ and will give you lovely crisp shots (little noise/grain).  

Most people tend to keep their digital cameras in ‘Auto Mode’ where the camera selects the appropriate ISO setting depending upon the conditions you’re shooting in (it will try to keep it as low as possible) but most cameras also give you the opportunity to select your own ISO also.  

When you do override your camera will choose a specific ISO you’ll notice that it impacts the aperture and shutter speed needed for a well exposed shot. For example – if you bumped your ISO up from 100 to 400 you’ll notice that you can shoot at higher shutter speeds and/or smaller apertures.  

When choosing the ISO setting Ask yourself the following four questions: 

  

1. Light – Is the subject well lit? 

2. Grain – Do I want a grainy shot or one without noise? 

3. Tripod – Am I using a tripod? 

4. Moving Subject – Is my subject moving or stationary? 

 

If there is plenty of light, I want little grain, I’m using a tripod and my subject is stationary I will generally use a pretty low ISO rating.  

However if it’s dark, I purposely want grain, I don’t have a tripod and/or my subject is moving I might consider increasing the ISO as it will enable me to shoot with a faster shutter speed and still expose the shot well.  

 

Assignment ISO Settings

Set your camera on manual so that your meter is at the 0 for perfect exposure by setting your ISO to 100 and then adjusting shutter speed and aperture to get a perfect exposure.  Start with your camera on a tripod or sit camera on a flat surface to take the same image with the same exposure each time only changing your ISO setting.  Number and keep track of each exposure and settings for each photo.  Start with your the lowest ISO setting (100) and continue to increase ISO in order until you are at your highest ISO setting.  Then upload your photos to https://www.snapfish.com use email address mrutan@adjcharter.org and password room107 and upload your photos to the site so we can view in class.  Good luck and see you next class. 

 

http://www.itsoverflowing.com/2012/01/photography-friday-iso/ 

 

From <http://digital-photography-school.com/learning-exposure-in-digital-photography/>