F/Stops 101 – A Concise Guide to Understanding Aperture

When I picked up my Pentax film camera – required equipment for my first university-level photography course – I had no idea what an f/stop was. Whether you’re using a similar manual camera or studying the features of your DSLR, perhaps you feel a similar trepidation.

We’re here to help, with all the ins and outs you need to know about camera aperture and f-stops. Welcome to F-Stops 101.

F/Stops 101 – A Concise Guide to Understanding Aperture

F/stops or f-stops measure how much light enters your camera’s lens, and therefore how bright your exposure will be. Depth of field and other results are also affected by the f-stop. How do you use f-stops in photography?

What Are F-Stops?

To understand f-stops, you first have to understand aperture. The aperture is the “hole” that allows light through the lens. Rotating blades inside the lens open to your desired aperture size when you press the shutter button.

Your camera’s lens functions much like your eye. When it’s dark, your pupil dilates to let in more light. When it’s brighter, your pupil contracts to allow less light to reach your retina.

Your camera’s aperture has the exact same function. You can increase its diameter to increase the amount of light entering the camera, and vice versa.

Each “stop” doubles or halves the amount of light entering the camera. Full stops include f/1.0, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22. Most modern cameras also facilitate 1/2 and 1/3 stops. So, moving 1/3 stop from f/9 to f/8 increases the amount of light by just 1/3.

Remember, smaller numbers indicate a larger aperture, while bigger numbers mean a smaller aperture. It seems backward, but it is an important fact to memorize when you start using aperture photography. More about that in our Frequently Asked Questions.

Do I Need to Change the Aperature on My Camera?

Whether you need to adjust your aperture depends on two factors – the type of camera you are using and the type of photo you wish to capture.

Point-and-shoot cameras and automatic settings on DSLR cameras determine the ideal f-stop for you. In this case, you don’t have to worry about setting the aperture.

Most DSLRs have an “Aperture Priority Mode,” usually marked on the menu or selection wheel with the letter “A.” In this mode, you can manually raise and lower the f-stop. You can experiment with this to see the results under different conditions. You can also change the aperture to achieve different effects, as when shooting long exposures or blurring moving objects (such as running water).

Some, but not all, lenses have an f-stop selection ring.

Some cameras, like the manual film Pentax mentioned at the outset, require manual manipulation of the f-stop in order to take clear, properly exposed photos. Many of these cameras have a built-in sensor to test whether your f-stop and shutter speed combination will result in a good exposure. On my Pentax, for example, I held the shutter release button halfway and looked for a tiny light in the viewfinder – green meant I was good to go, while red indicated that too little light was entering the camera. If your manual camera doesn’t have an indicator light, you’ll want to refer to an f-stop-shutter speed chart to ensure ideal settings.

What Aperture Settings Are Best?

The following list describes common photography scenarios and recommended f-stops.

  • f/1.2 to f/2.8 – Low light scenarios and portrait photography. The shallow depth of field makes the portrait subject stand out against the blurred background.
  • f/4 to f/8 – Works well for most scenarios. Offers contrast and a greater depth of field, allowing more objects at different distances to be in clear focus.
  • f/11 to f/32 – Best for landscapes and bright-light scenarios. With a wide depth of field, almost everything in the shot will be in focus.

F-Stop and Aperature Frequently Asked Questions (FAQs)

Still have burning questions about your camera’s f-stop and how to use it? We’ve got the answers you need.

How Will Changing the F-Stop Change the Picture?

The most evident effect of adjusting the f-stop is an increase or decrease in the brightness of the exposure. A larger aperture also results in a number of artistic effects. The depth of field is made more shallow, essentially blurring the background. Bokeh effects – out-of-focus circles of light – are also enhanced.

Another use of aperture is in reducing blur without a tripod. When you let in more light through the aperture, you can use a faster shutter speed. This quick shutter reduces blur from hand movement.

Are Aperature and F-Stop the Same Thing?

In a strictly technical sense, they are not, but essentially, they are. Technically, the aperture is the lens diaphragm’s physical opening. Different apertures – different sizes of the opening – allow different amounts of light to come through. The amount of light is represented by the f-stop, which is a ratio of the focal length of the lens and the diameter of the pupil or aperture. The terms “f-stop” and “aperture” are often used interchangeably.

Are F-Stop and Shutter Speed the Same Thing?

No, they are not. Both affect how much light reaches the camera’s sensor or film. The f-stop is the diameter of the camera’s opening, while the shutter speed is related to how long this opening stays open.

Which F-Stop Is the Sharpest?

Every lens has a “sweet spot” – an aperture value or f-stop that results in the sharpest photo. This value varies from lens to lens, but it generally falls in the range of f/5.6 to f/11.

Why Are Larger F-Stop Numbers Paired with Smaller Apertures?

Actually, they’re not. Think of each f-stop as a fraction. F/1.0 is 1/1, or the whole pie. It’s the largest aperture any camera can have. For f/8, you cut the pie into 8 slices, and you get the fraction 1/8. At f/22, you cut the pie into 22 slices – and those 1/22 slices are all smaller than your 1/8 slice.

What Does the “F” in F-Stop Stand For?

The “f” stands for “focal length,” referring to the focal length of the camera’s lens. If you substitute the focal length of your lens for the “f” and do a little math, you get the diameter of the camera’s aperture in millimeters. For example, if you’re using a 55mm lens and you set your aperture to f/4, you’ll get a fraction of 55/4. Divide 55 by 4 to get the aperture diameter of 13.75 mm.

Why Are F-Stops Included in Lens Names?

When a lens name includes an f-stop number, this is the largest or maximum f-stop supported by that lens.

Should I Buy a Low F/Stop Lens?

This will depend on the type of photography you do. Many zoom lenses have a maximum aperture of f/4 or f/2.8. These types of lenses are ideal for a wide range of photography. Some applications, however, require wide apertures and swift shutter speeds. Astrophotography is one example.

Prime lenses – those with a fixed focal length – have fewer moving parts, so they can handle wider apertures. Larger aperture lenses tend to be more expensive, so you should balance your equipment needs against the cost.

How Does ISO Relate to F/Stops?

F/stops, shutter speed, and ISO are the “exposure triangle” – the three aspects to consider when setting up your shot. Originally, ISO referred to film sensitivity or its ability to gather light. The higher the ISO, the better the film worked in low light. Today, the ISO refers to the sensitivity or signal gain of a digital camera’s sensor.

What does this mean for you? Imagine you’re shooting at an indoor event that doesn’t have great lighting. You could stop down the aperture to let more light into your camera. But then your depth of field becomes shallower, and you can’t get the background, foreground, and middle ground clear in the same shot.

Another option would be slowing your shutter speed to let in more light, but that causes blurriness from hand-shake. That’s when you adjust your ISO to a higher setting. You’ll use a flash and a mid-range f/stop. Everything will be in focus.

Changing these settings is a bit like working a puzzle in order to get the shot you want. Consider “playing” with all three settings to learn how they affect one another.