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BetterPhoto Q&A
Category: Exposure Settings

Photography Question 

Ziad H. Dabash 		 

Deciphering F-stops


There are f-stops and half f-stops on my camera. What are they exactly ? Are they related to shutter speed or aperture? How can I deal with it and calculate it? Thanks.


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February 28, 2005

 

Bob Cammarata 		  The aperture ring on your lens is broken down into f-stops. Each whole number represents a full stop (from f-8 to f-11, for example). In between any two numbers is a half-stop.

How you "deal with it and calculate it" depends upon your desired results.
The lower numbers will let in more light but will have less depth of field. The higher numbers will let in less light, but more of the frame will be in focus. Each aperture (f-stop) setting requires a corresponding shutter speed for proper exposure.


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February 28, 2005

 

Jon Close 		  F-stop numbers are a short and for expressing the diameter of the aperture opening as a ratio of the lens focal length. f/2 means the aperture diameter is 1/2 the focal length.

The "full stops" are a progression of the square root of 2 (~1.414).
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 are full stops.
Each full stop change lets in 1/2 or 2x as much light as the next. Because the f-number is the denominator of the ratio, larger f-numbers mean smaller apertures and less light let in.

Smaller changes can be made in 1/2 stop (x1.1892) or 1/3 stop (x1.1225) steps. f/4.5 is 1/3 stop smaller than f/4. f/6.7 is 1/2 stop smaller than f/5.6.


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February 28, 2005

 

Rodolfo Zarli 		  The answer is simple: f-stop is a measure unit of the light that hits your film in the camera: the light doubles from one stop to the next, as the shutter speed, that doubles the light from one speed to the next.

The formula is: light = speed + aperture.

So for the right light for your film(ASA) you can choose different speed and aperture.

Try it on ny camera simulator: http://www.zarli.it/photo/html/fotocamera.html


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March 03, 2005

 

Rodolfo Zarli 		 
 
 
The right link:
Camera simulator


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March 03, 2005

 

Ziad H. Dabash 		  thanks for all realy you help me to under stand it

thanks


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March 03, 2005

 
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