Photography 101 - The Basics
(c)Mark Overell 2013
- There is only one “correct” exposure for any single image.
- That is the exposure you, the photographer, chooses as appropriate for your image. The camera cannot choose it for you, it can make suggestions.
- By controlling the Aperture, Shutter speed and ISO, using and, if necessary overriding, the light meter.
- The size of the hole through your lens
- Written as f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22 etc.
- These are called Stops. Stop down to make the aperture smaller. Each reduction of these stops cuts the light in half
- The larger the number, the smaller the aperture and the less light gets through.
- DSRLs may have half or third stops.
- Apart from the amount of light, Aperture controls the depth of field (DoF). The distance range where objects are in focus
- Large apertures (smaller number) gives a small, or narrow, DoF, useful to separate the subject from the background, f/2
- Small apertures give large DoF, everything is in focus.
f is focal length
/ is divide by
So the diameter of the aperture of a 50mm lens at f/2 is 50mm/2 = 25mm
- The time the sensor is exposed to light.
- Measured in seconds or fractions of a second
- 1 sec 1/2 1/4 1/8 1/16 1/32 1/64 1/125 1/250 1/500 1/1000 etc
- Halve the shutter speed, need half the light.
- Controls the sharpness.
- Fast shutter speed freezes the subject
- Slow shutter speed lets movement be seen
Rule of Thumb
If you are hand-holding a lens don't try using a speed less than the focal length of the lens.
300mm lens = slowest shutter speed 1/300