Exposure Week 4
Questions to research and answer before next week’s Location Class on 5/6 March

1. What are the two ways exposure is controlled? And what are some other factors that play a role in exposure?

Exposure is controlled by the aperture of the lens (f-stop) and the shutter speed. These can be used in various combinations to get the desired effect. A large aperture will have a narrow depth of field as opposed to a larger depth of field with a small aperture. Shutter speed can be used to freeze action or create motion blur.

Exposure can also be controlled by the ISO of the film/sensor (sensitivity) and the intensity of the light

2. You have an ISO of 400, a shutter speed of 1/125th second and an f-stop of F5.6.

a) I ask you to open up the aperture to let more light in by 2 stops. What would you change your reading to? F2.8

b) Now, back at your original setting, close down three stops. What is your setting now? F16

3. What are three ways you can measure exposure?

In camera meter
Handheld meter
Histogram

4. If in a given situation ‘correct’ exposure is achieved by using 125 @ f8 at ISO 100, indicate the new shutter speeds required to provide ‘correct’ exposure for the other ISO settings below.

Film Shutter speed Lens aperture
ISO400 f8 1/500
ISO200 f8 1/250
ISO100 125 f8
ISO50 f8 1/60
ISO25 f8 1/30

5. If in a given situation ‘correct’ exposure is achieved by using 125 @ f8 at ISO 100, indicate the new f-number required to provide ‘correct’ exposure for the other ISO settings below.

Film Shutter speed Lens aperture
ISO400 125 f16
ISO200 125 f11
ISO100 125 f8
ISO50 125 f5.6
ISO25 125 f4

6. When you use a high ISO you get image degradation. With film this is called increasing the size of the grain. With digital we don’t refer to grain, we refer to ‘noise’ or ‘signal to noise ratio’

7. On your camera, what is the difference between AUTO mode and MANUAL mode?

In Auto mode the camera will select the shutter speed and aperture (and maybe the ISO). In Manual mode each setting is made by the photographer.

8. All in-camera meters try to render the scene as a mid-tone. So if the mid-toned scene is rendered appropriately, what will happen to the light toned scene (white)? And the dark toned scene (black)?

White will look grey and dark toned scenes will appear lighter.

9. What type of metering do built-in camera meters use?

Canon DSLR cameras use
Evaluative – the camera divides the scene into zones and averages them
Centre weighted average – measures the whole scene but gives more importance to the centre
Partial – measures a small area near the centre of the scene (8% on the 5D)
Spot – weighted at the centre (3.5% on the 5D)
Source: Canon EOS 5D Instruction Manual

10. If you are using ISO200 how more light sensitive will your exposure be if you change this to ISO400? (HINT: This is equivalent to 1 stop)

Twice as sensitive