F-STOP

On your camera each f-stop represented as a number ,up to the lens, and they can vary greatly. The smaller number the larger aperture (the opening of Diaphragm). Each F-Stop decrease or increase the light enter the lens. These f number increase by following

f1.0, f1.4, f2.0, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64, f90

As the size of the number increase the smaller aperture in diaphragm is, so the less light through the camera f5.6 allows x2 as much light through the lens as f8, f8 allows x2 as much light through as f11, and so on. Each f-stop can be divided into 1/3 or 1/2 stop which are as follows

(1/3 stop): f5.6, f6.3, f7.1, f8, f9, f10, f11, f13, f14, f16, f18, f19, f22

(1/2 stop): f5.6, f6.7, f8, f9.5, f11, f13, f16, f19, f22

The largest f-stop for this example is f5.6, allowing the most light into the camera and will also have the shallowest depth of field. This means that when focused on the main subject you want to photograph, the object on the front or behind it will remain out of focus (depending on how far they are from the main subject and on the focal length you use). As the f-stop decrease the surrounding objects become sharper

To get the full benefit of f-stop and Depth of Field you will need to understand the basics of light meter in you camera

-2..-1..{   }..+1..+2

•  

The • represents the current light meter. If it is positioned in the middle it means that the camera is set to correct exposure for the given amount of light. if the • goes to - side this means  that the camera is set to one or two f-stops under, if the • goes to + side this means  that the camera is set to one or two f-stops  over. So when photographing  and you see the light meter marker is at -1 and you camera set to f11, change the f-stop to f8 to open more aperture, like wise if at +1 change the f-stop to f16.

It's a good practice to take photo one stop under, one stop over and one at the correct exposure, so you can see the result which how each image come out; this call bracketing. some camera have an auto-bracketing mode which automatic took 3 or 5 photos at various f-stop. so you can choose the best photo you like.

To demonstrate the effect of f-stop affect the depth of field you will need to take about 5 photographs of the subjects with f5.6, f8, f11, f16 and f22 and you will notice that as  you decrease the f-stop the shutter speed will double, because the size of the aperture has decreased by half. Once you view the image above you will notice a slight difference between each image about depth of field ;  the larger aperture the less sharp background is. 

Some term and definition in this article

• Diaphragm : The device in the lens which control the amount of light entering the lens
• F-Stop : The size of the opening in the diaphragm of the lens, different f-stop allow a certain amount of light to enter the lens
• Depth of Field (DOF) : The amount of area in or out focus in the image.
• Aperture : The opening in the diaphragm which allow light in
• Shutter Speed :  The length of time the shutter remains open
• Exposure : The aperture and shutter speed combined