Light:
| Varies in intensity | Varies in colour |
| Sunrise | violet |
| Sunset | red |
| Sunshine | white - stark |
| Overcast | diffused |
| Midday | short shadows |
| Midnight | |
| Indoors | green or orange |
How to control light:
The amount of light getting into the camera is critical.
There are two ways of controlling it ... accurately.
-
Shutter Speed, and
-
Aperture
Shutter Speed is the length of time a shutter remains open.
It could
be 1/8,000 of a second or 8 hours.
Aperture is the size of the hole through which the light passes.
f1, f1.4,
f2, f2.8, .......f32
The two combined control the exposure.
Exposure
- exactly the right amount of light must hit the film to expose it correctly.
At any given moment, the amount of available light is a measurable commodity.
Camera Settings:
As discussed before, the amount of light hitting the film is critical, and the amount of light entering the camera can be controlled by making camera setting adjustments ... Shutter Speed and Aperture
Shutter Speed:
Shutter speed can range from 1/8000th sec to 8 hours or more. The amount of light getting on to the film is exactly halved or doubled by halving or doubling the time the shutter is open... makes sense?
So, 1/2 sec will let in double the light that 1/4 sec will.
Likewise 1/250th sec will let in half the light that 1/125th will.
Aperture:
Aperture can range from f1 to f32.
The amount of light getting to the film is exactly halved or doubled by halving or doubling the size of the aperture hole (which is measured in f numbers).
f numbers are the same for all lenses. Therefore f8 on a 24mm lens will let in the same light as f8 on a 200mm lens.
f8 will let in double the light that f11 will.
Likewise f22 will let in half the light that f16 will.
The
Exposure:
Shutter speed and aperture are related such that if you halve the shutter speed and double the aperture you are still allowing the same amount of light into the camera
for example, an exposure at 1/125th sec and f16 is exactly the same as 1/250th sec and f11 or exactly the same as 1/60th sec and f22
|
The
Relationship: |
||||||||||
| Shutter speed | 1/8 | 1/15 | 1/30 | 1/60 | 1/125 | 1/250 | 1/500 | 1/1000 | 1/2000 | 1/4000 |
| Aperture | f22 | f16 | f11 | f8 | f5.6 | f3.5 | f2.8 | f2 | f1.4 | f1 |
All the above shutter speed/aperture combinations give exactly the same amount of exposure.
How to measure the light -
Light Meters:
Available light is measured by a light meter. Light meters can be hand held or built-in to the camera.
A simple
built-in light meter gives a simple indication of the correctness
or otherwise of the exposure.
A more
advance built-in light meter will tell you what camera settings to
make or even make the settings for you.
Very advanced cameras such as the F5 have several modes of metering the light
-
Spot metering
-
Centre weighted metering, and
-
Matrix metering
Hand held light meters can be very accurate (and very expensive).
Setting the Camera:
How do you chose the right shutter speed/aperture setting to take a correctly exposed photograph in a given light source?
The best answer is - chose one and let the camera choose the other!
For example choose to shoot at 1/60th sec and allow the light meter inside the camera to nominate the correct aperture.
Or choose f8, for example, and allow the light meter to work out which shutter speed is correct.
Hint: Don't look at the list above. Those combinations are only valid for one theoretical light source.
 |
|
Notice, in this picture, (click on the image to enlarge) how the shutter speed - 1/100th of a second - failed to freeze movement in the man and his spear, but was quick enough to perfectly freeze the shield which wasn't moving as much. This is not a flaw, however, adding to the sense of action. |
What affects your choice?
Choosing a Shutter Speed:
What shutter speed should I use? What are the factors affecting my choice?
Answer(s):
-
Aperture setting
-
Subject movement
-
Camera movement
-
Lens size
-
Available light
-
Tripod
-
Artistic effect
-
Film speed
All these
considerations may affect your choice of shutter speed in some way ...
we'll discuss them in the next chapter.
Chapter
1
Chapter 2
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Digital Cameras