Thanks to member Bigdazzler
for this information:
The Exposure Triangle - Shutter Speed, Aperture, ISO Sensitivity
These three things will determine the exposure, ie. how bright or dark, of all pictures you take with your DSLR,
and how they will ultimately look.
Shutter Speed - Shutter speed is the amount of time the shutter is open whilst taking a picture.
Most entry level DLSR cameras offer shutter speeds variable between 1/4000th of a second
(a very fast shutter speed) and 30 seconds ( a very long or slow shutter speed, commonly referred to
as a " long exposure.") The time that the shutter is open when you take a picture determines how much light
will reach your sensor. Think of your sensor as like a roll of film, the sensor records everything that the camera
sees through your lens. Your chosen shutter speed, along with your chosen "aperture" and ISO ( see below )
will in part determine how bright or dark your picture will be.
Aperture - The "aperture" is an adjustable diaphragm, or hole if you like, inside your lens which can be opened
and closed to different sizes. Different settings, or variable sizes of the hole are commonly referred to as "f-stops"
and are indicated in "f numbers" on your LCD screen and/or in the viewfinder of your camera.
For example, f/2.8 , f/3.5, f/4 , f/5.6 , f/8 etc. The "f/stops" or "f/numbers" on your camera screen can be set at
certain intervals or "stops" usually up until a "f number" of around f/22 , and sometimes beyond.
These "f numbers" or "f stops" are indicative of what size the hole is set at within your lens.
IMPORTANT: Smaller numbers mean the lens "aperture" (ie. diaphragm or hole) is opened up to a larger size,
allowing more light through the lens. Larger numbers mean a smaller "aperture", resulting in a lot less light
travelling through the lens and reaching the sensor.
It sounds kind of backwards , large hole small number .. and ... small hole larger number .. but you will get used to it !!
Think of it in terms of as you close the aperture or hole in the lens to a smaller sized hole, resulting in less light being
allowed to travel through the lens and onto the sensor, you are "stopping" ( remember f-"stops" ) down the lens.
Lens apertures or f-stops can be chosen or set manually by the photographer to achieve different results in your final picture.
Aperture settings not only affect the amount of light entering through the lens but will greatly affect a creative aspect of
DSLR photography called " Depth of Field", or the amount of sharp focus within an image. But that's another discussion
ISO - ISO (pronounced "eye so", from the Greek Isos) is an abbreviation of 'International Organisation for Standardisation'.
Not important really but there you have it anyway !! Click here for the gory details if you really feel the need.
ISO is a measurement of how sensitive your cameras sensor is to light entering through the lens and/or shutter and
is measured in these numbers. eg. ISO 100 , 200 , 400 , 800 , 1600 , 3200 and sometimes 6400 on much more expensive higher end cameras.
Most DSLR cameras will also have an ISO AUTO setting.
You will notice the ISO numbers DOUBLE at each interval , this indicates that the sensitivity of your cameras sensor DOUBLES
each time the ISO setting is increased. Increasing your ISO means that you will need to adjust either your lens Aperture and/or
shutter speed to compensate for the increased sensitivity of your sensor.
REMEMBER: ISO , APERTURE AND SHUTTER SPEED ALL CORRESPOND TO AND WORK WITH EACH OTHER TO OBTAIN CORRECT EXPOSURE:
That's why we call it the Exposure Triangle , they are all as important as each other !!
Now there is a whole lot more to learn about these three critical elements but I hope this has given you a good basic definition of what
the Exposure triangle consists of and how each of the three important elements does their individual jobs in creating correct exposure for your pictures.
Traditional f-number scale
Each stop is half (lager number) or twice (smaller number) the light (aperture opening area)
f/# 0.5 0.7 1.0 1.4 2 2.8 4 5.6 8 11 16 22 32 45 64 90 128
Typical one-half-stop f-number scale
f/# 1.0 1.2 1.4 1.7 2 2.4 2.8 3.3 4 4.8 5.6 6.7 8 9.5 11 13 16 19 22
Typical one-third-stop f-number scale
f/# 1.0 1.1 1.2 1.4 1.6 1.8 2 2.2 2.5 2.8 3.2 3.5 4 4.5 5.0 5.6 6.3 7.1 8 9 10 11 13 14 16 18 20 22