Photography - Knowledge

F-stop in DSLR Photography: A Quick Guide to Know All the Details

7773 Views - 8 mins read

Beginning to click feels like entering an all-new world in itself. With everyone talking funny, obsessed with details, F-stop in DSLR photography, puts beginners into a muddle. Worry not! Here’s your chance to understand F-stop in DSLR photography. 

What is f-stop

DSLR camera lenses have a mechanism called the iris, whose function is to control the opening of the camera aperture. The aperture can be defined as an adjustable opening that allows a desired amount of light to reach the sensor of the camera.

The distance between the rear of the lens and the sensor is the focal length of the camera.

The f-ratio, f-number, or f-stop in DSLR photography is a unit used to measure the ratio of the focal length to the diameter of the aperture.

Alternatively, the aperture is measured in a scale called the f-stop. This scale varies from 1 to 32. As the f-stop number increases, the aperture becomes smaller, thereby allowing less amount of light to enter the lens. Therefore, an f-stop of f/2 will allow twice more light than an f-stop of f/4 to reach the lens.

How is f-stop calculated

In order to understand the calculation of f-stop in DSLR photography, you should first know the f-stop scale: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. Every stop decreases the aperture size by 50%.

The simple mathematical concept to calculate f-stop is explained below:

- The  Diameter of the lens divided by 2

(i) For a 50mm lens with the aperture of f/2:

the diameter of the lens/2

= 50mm/2

= a lens opening 25mm wide.

This is now the diameter of the aperture. Since the area of a circle is calculated as pi X r², therefore, the area that will be exposed to light will be 3.14 X 12.5 = 490.625mm².

(ii) For a 50mm lens with the aperture of f/2.8:

the diameter of the lens/2.8

= 50mm/2.8

= a lens opening 17.85mm wide.

This is now the diameter of the aperture. Using the same equation as above, we get an area of 250.31mm². Now comparing it from the above figure, it can be seen that now the area is halved.

Thus, an increment of 1 stop in the f-scale reduces the light by half.

At f/1.4 the aperture is wide open and allows a lot of light to reach the camera’s sensor. The f-stop f/1.4 is to be used for a shallow depth of field when the background needs to be blurred and the foreground is to be kept sharp. The f-stops in the middle range can be used for various levels of focus along the spectrum.

What Does the Number Mean

F-Stop or relative aperture defines the ratio of the lens’s focal length to the pupil diameter.

It actually is the measure of glass speed.

Try having a look at the picture here and analyze colors, brightness, clarity etc. The images signify how varying the focal length or F-number gets a blown-out effect in the first one. On the other hand, for the one on your right, aggregating the numbers produces a sharper and clearer picture.

F-stop in DSLR Photography: Know Which One to Use!


So, the figure is arguably important to give any picture a creative outlook.

F-stop in DSLR photography controls the depth of field, monitoring the amount of light hitting the camera sensors.

Furthermore, closing or opening the aperture/lens is hooked on the shoulder of shutter speeds, which is further subject to ISO.

Factors Used in Defining F-stop

The factors counted in defining F-stop in DSLR photography are listed below.


Inside any DSLR camera glass, the mechanism that controls the amount of light entering the lens and being processed by camera sensors is IRIS. The opening is named aperture. This stresses acquaintance with F-stop, aperture, and iris.


The aperture reins the lens opening. It is important when the background being captured is distorted or the subject under study is prime.

How to use the aperture-priority mode?

The aperture-priority mode is used when more control on the aperture is desired. This can be accomplished by choosing the mode “A“ (or “Av”) in your camera (it might vary depending upon the manufacturer and the model number). When using this mode, the camera automatically adjusts the shutter speed.

This mode can be used in controlled lighting situations for shooting still objects when the camera is mounted on a tripod.

It is worth mentioning that when using this mode, you will have practically no control over the shutter speed and yet this is the most popular setting among experienced photographers. This mode lets you play with the depth of field.

For example, if you wish to capture a picture of a subject next to a bright lamp, a fast shutter speed will be required.

On the other hand, if the subject is in a dimly lit area, a slower shutter speed will be required. In either of the cases, using the aperture-priority mode will automatically set the shutter speed.

Even if the elements comprising a scene are sharp, an aperture is important.


A larger F-stop value signifies a smaller aperture, aiming at less light entering the lens.

A smaller F-stop value results in a larger aperture, allowing more light.

The chart for beginners below will definitely help.

Aperture - F-stop in DSLR Photography


Drawbacks of the Aperture-priority mode

The aperture-priority mode is good for a well-illuminated environment when the subjects are stationary. However, when the subjects are moving or the lighting changes frequently, this mode is not recommended as the photos might be blurred. 

Know all the details for What is Aperture in Photography

Depth of field

How an image is exposed to the depth of field is part of DSLR photography 101.

So, what is the depth of field?

The distance between the nearest and farthest objects in a photo is called the depth of field, or DOF. DOF determines the sharpness of the objects in the photo.

If the background in a photo has to be blurred with respect to the subject, then a shallow depth of field will be required so that only a small area has the sharpness.

How does f-stop affect the depth-of-field?

As the f-stop increases, the aperture size decreases and a lesser amount of light is let in. Therefore, most of the objects in the image appear sharper. For all the objects in the photo to be in focus, or in other words, for the complete photo to have the same sharpness, a larger f-stop should be used.

Large F-Stop = Small Aperture = Large DOF

Small F-Stop = Large Aperture = Small DOF

Setting the Correct f-stop

In order to control the aperture size, the f-stop can be varied by using the camera’s manual or aperture priority mode. The best way to determine a desirable f-stop is experience or the trial-and-error method. In simple words, if you want all the objects in the photo to have the same sharpness, use a higher f-stop. The f-stop f/16 or f/22 is a popular setting among photographers when they want to keep the foreground and the background in focus.

Read on to know about Shooting with a Shallow Depth of Field

Shutter Speed

There are other factors other than f-stop and DOF that also should be considered in order to capture a good photograph. Determining the right shutter speed and sensitivity in DSLR photography is essential.

Responsible for exposure, it is the camera gear drive (mechanical or electronic) that controls light hitting the sensors.

Shutter in F-stop in DSLR Photography


Shutter refers to the mechanical or electronic control that allows light to hit the sensor and therefore is responsible for the duration of the exposure.

When shutter speed and F-stop numbers are linked, defining kith and kin, it makes concepts easier to hold and memorize.

Fast shutter speed or higher f-number => stops action

Slow shutter speed or lower number => denotes motion

Remember, slow shutter speeds will spectacle shaking the camera.

Check out The Perfect Handbook on Shutter Speed

Shutter speed stops

The shutter speed is calculated as 1/s, where s stands for seconds.

This speed determines how fast or slow will the camera’s shutter open and close.

A fast shutter allows capturing a fast-moving subject, whereas a slow shutter is used for nighttime photography with artificial light.

Check out the Complete Guide on Shutter Speed Chart (Cheat Sheet on How to Master it)

Shutter speed


The acronym ‘ISO’ stands for International Standard of Organization and stated as “Iso” by photographers. The term aims at making you cognize how alterations on the scale affect glow.

The word ‘glow’ is mostly used to signify women, but here, it is typically about pictures being clicked. Rephrasing the statement for clarity, consider clicking in the golden hours. For those to whom the term seems new, it’s the hour shortly after sunrise and before sunset!

The angle of the sun at this hour produces magical, golden light.

Know all about Golden Hour Photography: Learn all about The Magical Concept



ISO sensitivity or ISO stops

The actual meaning of ISO has been lost over the years, but it is a very important feature in photography. This setting is used to adjust the sensitivity of light for the camera’s sensor. The image sensor can change the light sensitivity in the camera based on the selected ISO setting.

A higher ISO will allow shooting in dim lights, but the picture will be very grainy. The range starts at 100 and goes up to 25600.

Most photographers alter the ISO settings as a last resort.

Thus, the three stops in photography, i.e. f-stop, shutter speed stop, and ISO stop, have to be in absolute sync in order to capture a good photograph.

To know more about ISO, read: Understanding ISO in simple steps!

Last but not the least, despite all the tutorials and explanation, practice is the best way to learn.

Not getting carried away, customize the value at ISO 1600 or 3200 and Snap! Change to ISO 100 or 200 (lowest on the scale) and click o’er. Compare!! You will categorically notice, one with ISO 100/200 are unblemished, compared to the one with higher ISO.

Don’t just run into conclusions. There’s still room to explore more. So, reverse and click. Dead-on! ISO is scheming exposure using the camera software, making it light sensitive.

Don’t forget to share experiences and comments

And yes, if we did miss something, tag us or leave comments.