New To Photography:f/stop chart

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This page is a chapter in the book Experimenting with Aperture.
As you have read above DoF is controlled by Aperture. This chart helps with exposure, each row of the chart represents the same amount of light (exposure) assuming the same ISO setting (say ISO 200).

The only difference is the DoF (depth of field) which gets smaller as you go down the list.

It turns out that each f/stop is about half the light (opening) as the next one and the shutter speed is roughly twice as fast.

Shutter Speed f/stop
1/4 second f/45
1/8 f/32
1/15 f/22
1/30 f/16
1/60 f/11
1/125 f/8
1/250 f/5.6
1/500 f/4
1/1000 f/2.8
1/2000 f/2
1/4000 f/1.4
Explanation of the numbers: Doubling or halving ISO sensitivity -or- shutter speed = one f/stop as per the chart above.

f/stop is a representation of area being the amount the lens is open to light. So f/1.4 is twice the light of f/2, which is twice the light of f/2.8 etc.
Maths: The square root of 2 is very approximately... 1.4 squared is 2; 2 squared is 4;
2.8 squared is 8 and so forth - so the term stop means half or double the area and therefore amount of light;
each stop number is multiplied by 1.4 of the lower previous number; this is because 1.4 (approximately) is the square root of 2).
A better approximation: 1.41421356237309504880168872420969807856967187537694807317667973799...

ISO is sensor sensitivity in a linear scale so halving or doubling ISO sensitivity therefore = one f/stop. At this stage of the learning plan we recommend you leave your ISO setting fixed at 200 so you don't have to worry about it for now.

Shutter speed is the amount of time the sensor is exposed for a photograph so halving or doubling that time is also = one f/stop.

Explanation of f/xxx: (this part is technical) The reason that both the halving and doubling and the smaller numbers mean more light things make sense is that the f/stop is a ratio. The ratio is between the diameter of the aperture in the lens and the focal length of the lens. The focal length is generally measured in millimetres (mm). On a 50mm lens f=50, and f/2 is saying that the diameter of the aperture is 25mm. The ratio is this 50/25 = 2.

- We write f/xxx (lowercase f slash number) not Fxxx or F/xxx (f = focal length)
- We can also write 100/2.8 in reference to a 100mm lens with a max aperture of f/2.8 (eg. the 'Pentax SMC-FA 100mm f/2.8 macro' can be describe as 'Pentax SMC-FA 100/2.8 macro' lens)
- The balance between aperture, shutter speed and ISO sensitivity is called the exposure triangle

Previous: New To Photography:Experimenting with Aperture Experimenting with Aperture Next: Experimenting with Shutter Speeds

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