Understanding F-Stops

Definition

F-Stop is a unit to express how much light is entering a camera lens. Example f/2, f/4, f/8, etc.

Explanation

Assuming this post is for beginners I am briefing out the dependent terminologies:

Aperture: Just like our eyes, camera lens has an opening that allows light to enter into the camera. This opening is termed as aperture.

Focal Length: Distance between the image sensor and optical center of camera lens. When you buy a lens for your camera, it will have a number on it, something like 18mm, 55mm, 105mm, etc. These numbers are called as focal length.

image001

Letter “F” in F-Stop is called as focal length. Focal length divided by aperture determines the F-Stop.

Calculating F-Stop

For a 200mm lens with an aperture 50mm:

F Number = Focal Length/ Aperture

= 200/50

= 4

Finally denoted as F/4

For a 200mm lens with an aperture 25mm (decreasing the opening):

F Number = Focal Length/ Aperture

= 200/25

= 8

Finally denoted as F/8

Focal Length Aperture F-Stop Conclusion
200 mm 50 mm F/4 Bigger lens opening results in smaller F-Stops

More light enters when F-Stop is small

200 mm 25 mm F/8 Smaller lens opening results in bigger F-Stops

Less light enters when F-Stop is large

How does this affect your photography?

Change in f number has a…….

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