Because good photography depends on being able to execute two things well:
Exposure
Composition
Exposure
A combination of three factors sometimes known as the Photographic Triangle:
Shutter Speed
Aperture
ISO
Or
how quickly light is being captured through how big an opening onto how sensitive a surface
Shutter
A cameras shutter covers the hole through which light enters to expose the sensor or film.
The shutter release button causes the shutter to open for a certain amount of time, then close again. Image source: www. howstuffworks .com Image source: VisibleDust
Shutter Speed Fast
1/1600 sec., stops action
Shutter Speed Slow
Silky, cool, edgy effects
1 sec. 3 sec. 1/3 sec.
Shutter Speeds
Open too long, photos are washed out (overexposed)
Not long enough, photos are too dark (underexposed)
Expressed in seconds: 1/8000, 1/4000, 1/2000 1/1000, 1/500, 1/250, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1 second, 2 seconds, etc.
Each setting is half or double the speed of its neighbor.
As the amount of available light decreases by half, the shutter speed needs to slow by double.
As the amount of available light increases, the shutter speed needs to increase
Aperture
The opening through which light enters the camera.
Sometimes called an iris because it imitates the opening in the human eye. Image source: www.howstuffworks.com
Aperture
The size of the opening is expressed as an f-stop number : 1.42.02.845.68111622
Each number represents an opening size that is half or double its neighbor
The larger the number, the smaller the opening
For all the science types: the f-stop is actually a ratio between the diameter of the aperture in the lens and the focal length of the lens:
e.g. f/2 on a 50mm lens says the aperture is 25mm. 50/25 = 2.
(Source: A Tedious Explanation of the f/stop by Matthew Cole)
For the rest of us: the size of the opening controls the depth of field in the photograph.
Aperture And Depth Of Field
f/5.6
Shallow depth of field
f/22 Deep depth of field
Aperture And Depth Of Field
Caused by refraction of the light hitting the edge of the opening
Rays scatter and overlap instead of going straight on its way to the sensor or film
The camera sees multiple images, resulting in blur.
The smaller the opening, the less surface available to scatter the light, resulting in less blur.
Bottom line: the aperture is used to control how much of the scene is in focus.
Aperture And Shutter Speed
The following reciprocals will yield the same exposure:
What changes is how much is sharp and in focus.
1/8 sec. f/22 1/15 sec. f/16 1/30 sec. f/11 1/60 sec. f/8 1/125 sec. f/5.6 1/250 sec. f/4 1/500 sec. f/2.8
The Light Meter
A device that assesses a scene and figures out the correct exposure
Modern cameras have them built-in
External handheld models also available
Engaged when shutter is pressed halfway
Matrix/Evaluative, Center-weighted, Spot metering
Looks for 18% Grey or Middle Grey
Easily fooled!
Tricky Metering Situations
Exposure Compensation
Used when the light meter is unable to evaluate the exposure as desired, or when correcting by whole stops is too much
Usually +/- 2 EV (Exposure Value) in steps of 0.3 EV
Available on most cameras
ISO
Sensitivity of the sensor or film to light
Represented by a number assigned by the International Standards Organization (hence, ISO) 100, 200, 400, 800, etc.
Again, each number represents double or half the sensitivity of its neighbor (Aint it wonderful!)
The higher the number, the more sensitive to light
Digital photography is cool because you can change the ISO from shot to shot!
Higher ISO = More Noise!
ISO 3200
So
Exposure depends on:
Shutter Speed how fast
Aperture how much
ISO how sensitive
And color is a function of:
White Balance how hot
And
Which camera you choose is a function of how much you want control those factors!
Cameras
Two popular types of cameras on the market for the consumer
Point-and-shoot SLR (Single-lens Reflex)
Cameras
Point-and-shoot
Viewfinder separate from lens
Small and compact
Fixed lens
Shutter delay
Usually fully automatic (some exceptions, like Olympus C-series)
