What is an f-stop? We’ve no doubt all heard this term used in photography circles. Instead of pretending to know what everyone’s talking about, let’s read on and develop a greater understanding of f-stops or f-numbers and how they have an effect on your images.
Words and Photography by Urth HQ
What Are F-Stops and F-Numbers?
Have you seen the ‘f’ that appears before a number somewhere on your camera’s display or in the viewfinder? Often it will appear with a forward slash or even as a standalone capital. Regardless, f/2, f2 and F2 are all the same and indicate that aperture is written as a fraction.
Need a quick refresher on aperture? Click here.
Although the little ‘f’ doesn’t stand for fraction, it does stand for focal length, because aperture is measured in fractions relative to the focal length of your lens.
Anytime you think about aperture from now on, think about it as a fraction of your lens focal length. f/8 represents 1/8th (one-eighth), f/4 represents 1/4th (one-quarter) and f/2 represents 1/2 (one-half).
If you’re using a 100mm lens, then your aperture or f-stop of f/8 (1/8th) means the actual width of your aperture opening is 12.5mm. Make sense? Let’s do one more. If you’re using a 50mm lens, then an f-stop of f/2 means the aperture diameter is 25mm, or close to an inch.
So, if someone’s discussing large or low aperture, they’re referring to an f-stop such as f/2 – f/5.6. And if someone’s discussing a small or high aperture, they’re referring to anything between f/8 and f/22.
Summary: An f-stop specifies the aperture of a lens as determined by the focal length of the lens divided by the diameter of the aperture.
WHAT IS F-STOP ON A LENS
Most manufacturers include an f-stop number in the lens name i.e. Nikon 35mm f1.8, which is generally inscribed on the lens body or rim to indicate the lens’ maximum aperture or aperture range. If you’re unsure of your lenses’ largest f-stop, have a quick look around the lens to find the markings.
There’s more information about the f-stop markings on lenses and the difference between fixed and variable apertures here.
WHAT IS F-STOP ON A CAMERA
All LCD displays on digital cameras will display the f-stop information. Again, keep an eye out for the little ‘f’ appearing before a number. If you’re shooting on the go, ensure the viewfinder display is available so you can adjust the aperture using the respective dial without shifting your focus from the scene in front of you.
What Does F-Stop Do?
F-stops are crucial components of photography and arguably what sets it apart from other two-dimensional mediums. It determines one third of the exposure triangle, aperture, which becomes priority for photographers and governs their photographic thinking.
Should I use a low f-stop or a high f-stop? Do I want the background out of focus or in focus? These are all questions a photographer asks him or herself before a shoot because they know how imperative their choice is and how it will translate visually.
F-stops’ main impact on an image, other than controlling brightness, is controlling the depth of field. If you’re new to photography and learning how to shoot in Manual Mode or in Aperture-Priority Mode, split your time between either low or high f-stops. Spend time strictly photographing at the opposite ends of this spectrum. This is a great way to quickly learn how f-stops control depth of field.
What a Low F-Stop Looks Like
Here are some low f-stop examples captured at f/5.6. How much separation is there between subject and background?
What a High F-Stop Looks Like
And here are some high f-stop examples. Notice how all of these photographs were captured at f/7 or higher? If you want to achieve the appearance of sharpness from front to back in your image, experiment with an f-stop of f/7 and work your way toward f/16. This f-stop range is used predominantly in landscape photography.
What F-Stop to Use
There’s no right answer. There is however, a general set of rules. But rules can always be broken.
Choosing the right f-stop is a creative decision. Do you want a shallow depth of field or a large depth of field?
If you and a camera are only newly acquainted, it’s best to develop an initial practice of photographing people with a shallow depth of field (low f-stop) and landscapes with a large depth of field (high f-stop).
WHAT F-STOP TO USE FOR LANDSCAPES
A distinctive feature of landscape photography is sharpness. This can only be achieved by using high f-stops because a large depth of field is created, keeping everything from foreground to background in focus.
F-stops between f/11 and f/22 are most often used for landscape photography. Make your first exposure at f/11 and work upwards from there. Do some test shots at f/22 to see how well your camera can handle this f-stop. A lot of digital cameras risk actually losing sharpness at that end of the aperture scale.
Generally, there is a sweet spot for landscape photography around the f/11 to f/16 mark. If a greater level of sharpness is required, you can learn more about the focus stacking technique here.
WHAT F-STOP TO USE FOR PORTRAITS
Deciding what f-stop to use for portraits is mostly a question of blur. How much do you want to isolate your subject from the background? Using a low f-stop between f/1.4 and f/5.6 will create a beautiful layer of depth to your images.
Portraiture is also largely dependent on your equipment. Only the best and most expensive lenses typically reach the f/1.4 mark, and when they do, they take an intermediate to advanced photographer to wield them because their depth of field is so shallow that the risk of missing focus is high.
Set your f-stop to f/5.6 and work down, lowering your f-stop until the desired depth of field is achieved. Be sure to review your shots as you go to make sure they’re in focus.
WHAT F-STOP TO USE FOR LOW LIGHT
Low light has a knack of removing your creative control because you need a low f-stop to brighten the image enough for a decent exposure, regardless of whether you want a shallow depth of field or not. This is why low light and night photography can be extremely challenging, and rewarding.
For low light scenes, you’ll most likely have to work in Manual Mode to adjust exposure settings without the restriction of any semi-automated modes.
You’ll need a tripod, as making a long exposure is almost guaranteed in low light. Your f-stop is dependent on whether you want a tack sharp image front-to-back or if you’re focusing on something in particular. You may need to increase your ISO to accommodate for the low light, but otherwise, just make adjustments to your shutter speed if required, leaving the f-stop in creative control of the scene. If you move the mode to Bulb, you’ll be able to make much longer exposures than 30 seconds with the assistance of a remote cable release.
As a general rule of thumb, you will want to choose a lower f-stop to allow enough light to pass through the camera. And because the scene is dark, a large depth of field may not be necessary.
Check out this f-stop chart that demonstrates how a change in f-stops alters depth of field.
By now, you should have a solid understanding of f-stops and how they influence your photographs. It really is simple, but can seem overwhelmingly complex for a beginner. Moving forward, take your f-stop findings and start experimenting with how high and low f-stops can alter your depth of field.