James Stanbridge
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The blog of James Stanbridge. Articles and education about photography.

Photography 101: Exposure

Photography is primarily about light – you need to control the light to create an exposure. The more light you allow through the lens, past the shutter, and onto the film or sensor, the brighter the exposure. The less light you allow through this passage, the darker the exposure.

If there’s more light in the scene, you need to let less light in, and the darker the scene, the more you need.

There are three aspects to exposure, and understanding these aspects is the crux of your task as photographer.

ISO, shutter speed, and aperture.

Your ISO level is how sensitive your sensor or film is to light. Aperture is how wide or narrow the opening is in the lens. Shutter speed is how long the shutter remains open during your exposure.

Creating a good exposure is all about how you balance these three aspects with each other.

You will need a tripod to create a long exposure photograph.

You will need a tripod to create a long exposure photograph.

ISO

ISO dictates how sensitive your film or sensor is to light. The lower the ISO, the less sensitive the camera is to light. The higher the ISO, the more sensitive your camera is to light.

ISO also affects the quality of your resulting photo. The higher you push the ISO on your camera, the more “noise” you allow into the image. The more noise your camera produces, the lower your quality of image will become. Details will begin to disappear, as the camera starts to render more noise. Some cameras perform better at higher ISO’s than other cameras, as they have stronger sensors that are more refined and prodcue less noise.

ISO is a doubling scale. ISO200 is twice as sensitive to light as ISO100, and so on. Some camera models allow ISO settings that are lower than 100, and some cameras have ISO capabilities that can be pushed over 100,000.

A good rule of thumb is to use the lowest ISO possible to produce a good exposure. Choosing the lowest ISO you can will allow you to preserve the details in your image, as the lower your ISO, the less noise there is to interrupt your camera’s rendering of fine detail. You can’t render a single hair if the amount of noise is too high.

Generally, if you are outside on a fine day, choose the lowest ISO your camera is capable of. As the day darkens, and moves into night, set your ISO just high enough to produce a good exposure.

A dark scene will require you to use a combination of higher ISO's and longer shutter speeds to capture enough light for an exposure.

A dark scene will require you to use a combination of higher ISO's and longer shutter speeds to capture enough light for an exposure.

How high you can set ISO on your camera is a balance between your cameras capabilities, and your own personal preference on how much noise is acceptable for the shot to be deemed a “quality” image. Test your camera out and get familiar with how your camera renders details at higher ISO’s. This differs from camera to camera, and there is no “right” answer.

Aperture

Aperture is how wide the aperture blades are open, and how much light you allow to pass through the lens into the camera.

Aperture is defined in ‘f-stops’. The lower your f-stop, the wider the opening is. Conversely, the higher your f-stop, the more narrow the opening is. This seems counter-intuitive at first, and to get past this, I like to think of the f-stop as being the distance from the outside of the lens barrel to the edge of the opening. Aperture has nothing to do with the camera, and everything to do with the lens you are using. The aperture blades are inside the barrel of the lens.

Aperture also has a creative element. F-stop controls what is known as ‘depth of field’, or DOF. Depth of field is the distance in-front of, and behind your focal point. The wider you have your aperture, the more narrow this distance. As you decrease the size of the aperture opening, the depth of field increases, and more of the shot will be sharp and in focus.

To create bokeh, open your aperture wide open, and force the areas not in the focal plane out of focus.

To create bokeh, open your aperture wide open, and force the areas not in the focal plane out of focus.

These out-of-focus (OOF) areas are often referred to as ‘bokeh’. Bokeh is really referring to the aesthetic quality of the areas that are OOF. How smooth it is, and how creamy and attractive the lens renders these areas. To achieve a blurry, ‘bokeh’-licious effect, you will need a ‘fast’ lens. One that allows a very wide aperture (for example, an f1.4 lens is very fast, and a f4 lens is less so). Typically, these lenses are more expensive than their cheaper counterparts. Fast lens are more difficult to make, and require special engineering and glass elements to allow sharp images at wide apertures. If you can afford one, get one!!!

Shutter Speed

Shutter speed is how long the shutter in your camera mechanism is open for. The quicker the shutter speed, the less light is allowed into the camera. The longer the shutter speed, the more light is allowed into the camera.

Shutter speed values are expressed in seconds, and fractions of a second. 30 seconds (30s) is a very long shutter speed, and 1/8000 of a second (1/8000s) is very fast. Many, many times more light is captured during a 30s exposure than is captured during a 1/8000s exposure.

On a bright day, you will need to use shutter speeds that are faster, as there is much more light in the environment. This amount of light being transmitted into the camera must be reduced by using a shutter speed that is not open for as long. As the day gets darker, you will need to use slower shutter speeds, so that the camera can be open for long enough to create a good exposure. To a point – if you leave the shutter open for too long, then your ability to hold the camera steady for long enough will be tested. Even subtle movements at slow shutter speeds are amplified, and the image will be subjected to ‘camera shake’. If it’s too dark to hold the camera steady, you will need to use a tripod, so that this camera shake is minimised.

Shutter speed also controls the capture of movement. The longer the shutter remains open during an exposure, the more movements of objects in the frame are captured. A car speeding through the frame and captured with a relatively slow shutter speed (say, 1/60s), will be almost entirely blurred, and not sharp. No part of the car can be captured with clarity, as the car moves across the entire frame during the exposure. A car speeding past (within reason) and captured with a 1/8000s exposure will be rendered with perfect clarity, as the car is not moving faster than the shutter. It doesn’t cross the frame nearly as much, as the shutter is open for only an extremely short period of time. It is “frozen”.

This effect, the blurring and freezing of motion using shutter speed can be used in artistic and creative ways.

Sometimes, you may want the subject that is in movement to be blurred, showing how fast they are going. This can be contrasted with a sharp background so that the viewer can see how dynamic the subject is.

Smooth, silky, flowing water can be captured by leaving the shutter open for many seconds at a time.

Smooth, silky, flowing water can be captured by leaving the shutter open for many seconds at a time.

Long shutter speeds of many seconds can be used to create smooth, silky, flowing water. Long shutter speeds can be used to capture stars, which although visible to the naked eye, are quite dark. Eyes are exceptional light capturing machines – and cameras have not quite caught up.

The Triad — Bringing it all Together

These three aspects make up the essence of exposure, and of photography. They need to be brought together in unison to create striking, well-exposed, aesthetically-pleasing, technically accurate, artistic images.

The common thought on how to imagine this balance is to picture a triangle. On each apex of the triangle is one of the three aspects. Achieving a good exposure is about choosing each of the three aspects to create a good exposure.

What the exposure triangle leaves out, is the artistic effect that each of your choices of ISO, aperture and shutter speed has on the resulting image.

A good way to approach your exposure, is to pick the particular artistic effect that you want to create with your image, and choose the other two to compensate. Some brief examples are:

  • Is quality of the resulting image important? The larger you print your image, the more apparent noise in the photo will be. It’s almost always a good idea to set this as low as you can after choosing the artistic effect you need. Sharper, crisper, less noisy images are the result. Cha-ching!
  • Is the subject moving and you want a dynamic image? Choose a slow shutter speed, and once this is set, choose the other two.
  • Is it a portrait, and you want to separate the subject with bokeh/blur? These images can be striking, and bringing the subject to the foreground and allowing the rest to blur away is a great way to isolate your subject.

Taking well exposed, artistic images is a constant balancing act. You need to be constantly aware of the effect that your decisions have on the images that you produce.

Practise

There is no substitute for practise. There really isn’t. To shoot artistic images that are well exposed, you will need to make this practise as intuitive as writing with a pen, or tying your laces.

If you’re serious about photography, you must force yourself out of your comfort zone, and learn to consciously shoot with ISO, aperture and shutter speed in mind. The only way to do this is to abandon auto mode, and turn the dial around to manual mode. Manual mode forces you to set each aspect individually.

Shooting manual will force you to think, and through this baptism of light, you will gain a better, more intuitive understanding of exposure. Through this practise, you will eventually understand this balance as well as the back of your hand.

So, go on, get shooting!