Essential guide to camera lenses

Don’t know your macro from your telephoto, or your prime from your zoom lens? Read the latest Clifton Cameras guide to camera lenses explained.

Represented in millimetres (mm), focal length is a rough measure of the point where light rays converge to form an image on your sensor. A lens that has a short focal length can give you a wider angle of view compared to the longer focal length and narrower angle of a telephoto lens.

One thing to bear in mind is that focal length applies to 35mm cameras or full frame sensors. For cropped sensor cameras, the actual focal length will differ.

Handheld focal length

When shooting handheld, your focal length can affect your ability to take crisp photographs. A longer focal length will pick up more vibration, so your hand shaking can cause images to blur. This means you’ll need a faster shutter speed to compensate. As a loose rule of thumb, your focal length in mm corresponds to a minimum speed. For example, a 300mm zoom will need a speed of 1/300 second.

Lens aperture

When you increase the shutter speed, your image is darker. To compensate you have aperture and ISO. A lens has its own aperture range, which is the amount the lens can open up, or close, to let light in. This is represented by F numbers. A wider opening has a lower number – so f/1.0 will yield a brighter image than f/4.0.

Aperture works in correlation with your other exposure settings. A higher f number (narrower aperture) requires a slower shutter speed, as it needs to let more light in. However, the depth of field is wider so more things are in focus.

A lower f number (wider aperture) lets more light in and needs a faster shutter speed, but is good for picking out a subject in focus.

Generally speaking, the better the maximum aperture (smaller f number), the more light the camera lets in which makes it ‘faster’ as you can set the shutter speed higher without darkening the image.

Zoom vs prime

There are two types of lens available for digital camera buyers. There are zoom lenses, which offer variable focal lengths and prime lenses, which offer one focal length. A zoom lens is a versatile option as you can switch between focal lengths at will without swapping lenses or moving. A prime lens is far lighter and smaller, but you’ll have to move in with your feet to get closer.

One major advantage of prime lenses is that they carry larger maximum apertures which allows more light in, better for low light conditions and shooting with higher shutter speeds.

Lens types

With this knowledge of aperture and focal length, selecting your next lens is a matter of application. You’ll need to know what you’d like to shoot and then select a lens based on your needs.

Wide Angle Lens

With a focal length of 21-35mm, a wide angle lens is perfect for landscape photography. Selecting a prime lens with a high maximum aperture is a good way to grab sharp shots in various lighting conditions.

Best for: landscapes

Prime lens

While we’ve already discussed prime lenses, we feel they deserve their own mention under types. Two very common prime lens focal lengths are 40mm and 50mm, which are ideal for street portraiture. Because of the high maximum aperture afforded by a prime lens, you can create pleasing background blur and get sharp focus in lower light.

Best for: portraits and low light

Standard lens

There is no real ‘standard’ lens, but generally they apply to lenses that have a focal range similar to the sensor size. Most ‘kit’ lenses that come with cameras are 18-55mm zoom lenses which allow you to get a range of shot types. However, they generally suffer from inferior apertures and are more generalist in their approach. That said, they’re ideal for versatility and will often do the job of multiple lenses.

Best for: versatility

Telephoto lens

Want to shoot sports or wildlife? You’ll need a telephoto lens that lets you get up-close and personal without disturbing things. A lens is considered telephoto once it has a focal length past 70mm – but this number can be as high as 135mm.

A zoom lens lets you do this, but be aware that the further you zoom in, the more vibration you’ll see so it may be worth using a tripod or a faster shutter speed. These lenses have a wide focal length, and a telephoto one and the maximum aperture will vary depending on your zoom level.

For example, a 55-250mm lens has a 55mm max wide focal length and a 250mm max telephone length. The maximum aperture listed on the lens will apply to the wide focal length. This will reduce as you zoom in, meaning less light enters the sensor – so the image may be darker if you can’t compensate with a slower shutter speed and ISO.

A superzoom lens is a variant of a telephoto that has a wide range such as 18-300mm. Telephoto in the strictest sense applies to lenses that begin in higher zoom ranges (such as 70-300mm.)

Best for: wildlife

Macro Lens

While you may see Macro lenses with telephoto-like focal lengths (100mm is a common macro lens size) – their application varies significantly. A macro lens is considered to be a lens which reproduces an image at a minimum of a 1:1 ratio when focussed as close as possible. Some lenses are marked as macro that produce images at ratios like 1:3 and 1:2 but these are not ‘true’ macro.

What 1:1 means is that the image projected onto your camera’s sensor is the same size as the object. Unlike a regular lens held close a subject to achieve this ratio, a macro lens can find focus at close distances. Non-macro lenses will not be able to focus on objects closer than their minimum focus distance.

Some macro lenses are capable of much higher magnifications, such as 4:1 – which means the image on your sensor is 4x larger than the subject.

Best for: you guessed it, macro!

Feel free to contact us via email or on 01453 548128, and we will happy to answer any questions you may have.

By Andi Thomas
22 Apr 2016