Understanding focal length
What does the focal length of a lens mean and what difference does it make? Read our handy guide to be in the know
Camera lenses are usually described by two main factors. One is the aperture or f-number, the maximum size of the hole where light gets through to the sensor (the lower the number, the bigger the hole). The other is focal length, which is in millimetres. You will usually see lenses described by focal length first and then aperture, for example 85mm f/1.2.
Focal length isn’t a measurement of the actual length of your lens – you can find two 85mm lenses that are completely different in size. Focal length, in fact, is the distance between where light rays converge in the lens to form a sharp image and the sensor.
Focal length defines magnification and angle of view
The most important thing about focal length, however, is not what it is, but what it does. Focal length defines two main things about any lens: its magnification and its angle of view. And, as one goes up, the other goes down. For example, a 24mm lens has a wide angle of view and low magnification – perfect for sprawling landscapes. A 600mm lens, however, has a very narrow angle and view and large magnification – great for taking close-up shots of faraway wildlife (especially useful when you don’t want to get too close to a lion!).
Nikon Z 7 with NIKKOR Z 70-200mm f/2.8 VR S
Long focal length: shallower depth of field
But there’s more. Lenses with longer focal length tend to have a shallower depth of field, meaning you can focus on a particular object far away, whereas shorter lenses have a deeper depth of field, which means you can get more objects in focus throughout the image. The focal length of a lens also affects the perspective of an image. With a long lens, perspective tends to be compressed, whereas with a wide-angle lens the relative distance between two objects appears greater.
Nikon Z 7 with NIKKOR Z 70-200mm f/2.8 VR S and TC-1.4
Focal length on a DX camera is different to FX
Choosing lenses can often be a complicated process, especially with so many options in the Nikon Z mount range, not to mention access to another 300 or so Nikon F mount lenses with a Mount Adapter FTZ II. So, here’s a quick guide to the different focal lengths and what they often get used for. You should also bear in mind that focal length translates differently on a DX camera (such as the Nikon Z 30, Z 50 or Z fc) compared to an FX ‘full-frame’ camera, as the sensor on a DX camera is 1.5 times smaller than the FX sensor. For example, if you put a 50mm lens on a DX camera you will actually get the angle of view and magnification similar to an 75mm lens on an FX camera (because 50 x 1.5 =75).
Primes vs zooms
There are two types of lenses: primes, which have a fixed focal length, and zooms, where the focal length is variable. Zooms are super-handy, often meaning you only have to carry one lens around, as it's capable of shooting lots of different subjects, from landscapes to portraits. So, it’s perfect for when you are on the move. Prime lenses, however, are lighter and often have larger apertures for getting beautiful blurry backgrounds.
Nikon Z 7 with NIKKOR Z 70-200mm f/2.8 VR S and TC-20
Ultra-wide angle: 8mm to 24mm
Any lens with a focal length of between 8mm and 24mm is usually described as an ultra-wide. You’ll be taking in a huge angle of view of what’s in front of the camera. These are lenses for getting in really close with your subject to create drama and are also used extensively for astrophotography. However, at really low focal lengths there will be significant distortion at the sides of the image where straight lines start to look curved. Ultra-wides are one the hardest lenses to master but, with effort, they can deliver incredible results.
Wide angle: 24mm to 35mm
From 24mm to 35mm, lenses are wide angle. These are beloved by landscape, interiors and architecture photographers, as well as being useful for street scenes and dramatic pictures of the night sky. Get close to your subject and you will accentuate the perspective in the scene. A wide angle is a great travel companion, allowing you to shoot landscapes, cityscapes, people and much more.
Standard: 35mm to 70mm
From 35mm and 70mm, we have the ‘standard’ focal length, which is pretty close to what the human eye sees. Photographers talk about the ‘nifty fifty’ – a large aperture 50mm prime lens such as the NIKKOR Z 50mm f/1.8 S – because a 50mm lens is an ideal day-long companion, suitable for so many different types of shooting, especially in low light situations or indoors. This type of lens also creates a shallow depth of field and great bokeh blur.
Super-telephoto: 300mm upwards
At 300mm and upwards, we have the super-telephoto range, which is most commonly used by sports and wildlife photographers, where it would be impossible to get close to the subject. At this range, and with such a narrow angle of view, it’s usually advisable to use a monopod or tripod to reduce camera movement (although Nikon’s in-camera vibration reduction (VR) and VR lenses can help with that), and also because lenses this size can be heavy to hold for long periods. Telephoto lenses can also be used with a teleconverter, which can double the focal length of the lens, giving you even more ‘reach’.
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