Digital Photography Tutorial

While exposure is a central interest for some, we don’t think it’s nearly as important in making good photo’s as other aspects like selection (with the selection of the point of view, cropping and timing) and creativity. So a few words about exposure.
We can use the same structure as on our other pages: flaws, oddities and extremes.

Flaws with exposure

 

When making pictures, the first thing you want to do is to prevent flaws. Considering exposure the flaws can in short be summed up by:

• The picture is

  not in focus

  (where it should be).
• There is

  motion blur

  , either by the subject moving, or camera shake.
• The photo is

  over exposed

   or

  under exposed

  .
• There is

  digital noise

  :
  

The other way round, the ‘right’ exposure would mean:

• Everything in the picture that should be in focus, is in focus (this is what it is all about for a beginning photographer).
• Other parts of the photo may be in focus, but may also be out of focus to attract more attention to the part that is in focus (this is what it is about for an intermediate and advanced photographer).
• There is no unwanted motion blur.
• There is no unwanted (digital) noise, due to limitations of the sensor of the camera (sometimes called the ‘CCD’).
• The photo is not over exposed neither under exposed.

For the exposure, four correlating factors come into play: brightness of the scene, shutter speed, aperture and ISO-speed. The right amount of light must be captured by the sensor of the camera. Not the right combination of these factors would create over exposure (a too bright picture) or under exposure (a too dark picture).

The amount of light captured by the sensor is a result of some basic mechanisms:

• The higher the

  brightness of the scene

  , the more light reaches the sensor. Pretty logical. This ranges from a photo at night without flash, to a sunny afternoon with loads of light.
• A slower

  shutter speed

   means a longer time of exposing light to the sensor, so in total more light reaches the sensor. An exposure time of only 1/3000th of a second lets the light through very short, and 1/15th or for example 4 seconds is long.
• The higher the

  ISO-speed

  , the more sensitive the sensor is for light. ISO-100 is not very sensitive (but high quality) and ISO-1600 is very sensitive.
  A big advantage of digital cameras in comparison with analogue cameras is: you don’t have to change film rolls to change the ISO-speed. You can change it with each photo, so in fact you have an extra factor you can easily play with.
• A bigger

  aperture

  , means a wider opening in the lens, so more light reaches the sensor. Keep in mind that the larger the f-stop number, the smaller the lens opening. An aperture of f/22 is very small opening for the light to get trough, an aperture of f/4.0 or f/2.8 is very wide open:
  

These four factors are interrelated. If one is increased, too much light would be captured, so another must be decreased, and vise versa.
                      

A right combination of these factors has to be chosen at the moment a picture is taken. With digital SLRs you can set or prioritize the factors. First you set the ISO-speed. If you choose ‘aperture priority’ (or ‘Av’), you can set the aperture, and let the camera computes the corresponding exposure time. If you choose ‘exposure time priority’, you choose the exposure time, and the camera the aparture.
With an automatic program setting you let the camera do the judgement, and let the camera evaluate what it thinks it is the best exposure time, aperture and ISO-speed given the lighting conditions. And the camera can even change the lighting conditions… by using the flash!

Things to consider are:

• To shorten the exposure time, you could increase the ISO-speed of your camera. But that also increases the

  noise

  , perhaps up to unacceptable levels. So here are boundaries. A camera that is capable of capturing at high ISO-speeds with little noise is a clear advantage. So a good way is to start with a ISO-level where the noise is minimal or at least acceptable.
• A longer exposure time brings a smaller aperture and a

  longer depth of field

  , meaning more things will appear ’sharp’ on the photo, so there is less focus on only a part of the photo. But this can mean that distracting elements on the photo will be more in focus and therefore be even more distracting. This might be wonderful in landscape photography where every detail of the landscape might be the part of the whole scene, but less effective in portrait photography where you want to bring attention to the subject, and not the background.
• A shorter exposure time brings a bigger aperture and

  shorter depth of field

  .
• Having an

  image stabilizing

   option on your camera reduces the effects of camera shake. This can move the boundaries regarding the factor ‘exposure time’. For example from minimal 1/60th of a second to minimal 1/15th of a second.

So the usual method is taking the right exposure as starting point (cameras work like this), and let that determine the other factors. But that is not all. Most Digital SLRs have settings to over expose or under expose:

‘exposure compensation

‘. And that is very practical.
At night a photo doesn’t have to be as bright as in clear daylight. Because a camera doesn’t take into consideration the difference whether it is night or day, it will try to expose the night time photo like it is daytime. But at night things are in fact dark, so why let it expose in the ‘correct’ exposure like daytime? So consider under exposing then, by setting the exposure compensation to -1 or even -2.

So now for the creative part, what’s it’s really about (not the f-stop numbers):

• Bring the attention to the subject, having the subject in focus, and the less important background out of focus. Especially the eyes are important to be in focus.
• Motion blur can also be a wonderful thing, suggesting motion dynamics:
  

Oddities with exposure

But hey, knowing what is ‘normal’, that gives room for some opportunities for oddites as we presented in our introduction to oddities.

• Removing the dynamics of a very fast moving subject (like a running horse or falling water) by capturing only a split second. The viewer has the idea that the subject must be moving fast, but it is frozen. That’s odd…
  
• You can deliberately over expose or under expose. At shooting time, or afterwards (with more control) with photo editing software.
• Viewing the normal world with your eyes, the depth of field of your vision is pretty long. With good eyes, nearly everything that you see is sharp, and the parts of your vision not in focus are not very blurred. So a photo with a short depth of field, with heavy blurring is in fact a bit odd view of the world.
  
• Draw attention to a different part of the picture than what is expected.
• Using the panning technique: follow the movement of a subject, like a racing car, with your camera. If executed well, this results in having the moving subject sharp and without motion blur, while oddly, the fixed background shows motion blur. For this, the exposure time must be long enough to create motion blur. If you photograph a racing car with a very short exposure time, it looks like it’s rather standing still on the track, and all the excitement of speed is gone.

Extremes with exposure

• An extreme short depth of field, like with macro photography. That’s not normal in the regular world.
• Extreme over exposing.
• Extreme long exposure times:
  

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