DSLR starters' guides: Lenses

Blogs
Tue 15 April

The beauty of DSLR is that you can attach a different lens to your camera depending on what and where you're planning to photograph.

Now that you’ve bought your DSLR and understand the basics of photography, it’s time to turn your attention to lenses. This is not a simple topic, and using an appropriate, high-quality lens will really change the way you take pictures.

Let’s start with two fundamentals: focal length and sensor size. Every lens is defined in millimetres, and this measure is called its focal length. This measurement is the distance between the sensor and the optical centre of the lens when the lens is focused on infinity. Without getting into the technicalities:

  • A short focal length allows you to stand close to your subject so that they fill the frame and things in the background seem farther away than normal. Examples of short focal lengths are 15mm, 20mm, 35mm.
  • A long focal length allows you to stand far away from the subject so that it still fills the frame, but that things in the background seem closer than normal. Examples are 85mm, 105mm, 300mm.

The focal length range is printed on the lens, in this case 18-200mm, for example, and the most commonly used focal lengths are indicated on the lens barrel - you can see 18, 24, 35, 50 and 70 in the image below.

Sensor sensibility

Now we need to go back to the camera, and specifically the image sensor. Some of the more expensive DSLRs come with a 'full-frame' sensor which is equivalent in size to a 35mm film negative. Most entry-level DSLRs are equipped with less than full-frame sensors because they are easier and cheaper to manufacture. You’ll need to take this into account when choosing a lens.

For example, a 'standard' 50mm lens has about the same focal length as our eyes, but when attached to cameras with smaller sensors, this shrinks to around 35mm. Put a 50mm lens on a DSLR with a full-frame sensor and it’ll act closer to a 80mm.

The above picture was taken on a full-frame camera using a 50mm lens. Had we been using a camera with a smaller sensor, we'd only be able to see the area defined by the black box. In other words, the view is less wide on non-full-frame cameras.

Types of Lenses

Some lenses are best suited for portraits while others are better for landscapes. There are no hard and fast rules and creative photography is all about breaking them. Generally speaking, portraits are best suited at longer focal lengths: 105mm, 85mm are traditionally known as portrait lenses, while landscapes have more impact with wide-angle lenses.

Lenses are usually grouped into different types:

Wide angle: 28mm or less, good for interiors and landscapes
Standard: from 35mm and 85mm, good for general use and portraits
Telephoto: from 100mm to 300mm, good for sports, portraits and wildlife

Wide Angle lenses allow you to fit a lot into an image. They are useful for landscapes and are great for documentary photography where you’d like to include a lot of foreground and background. One thing to be aware of when using wide angles is that there is some distortion at the edges, especially at the widest setting. Be sure to keep people in the centre of the frame otherwise they may look stretched.

An example of using a combination of a wide-angle lens and a large f-stop (f11) Foreground and background are sharp.

Above is an example of what happens when an ultra-wide-angle lens is used to take a portrait. In this case, a 16mm focal lens was used and you can clearly see that the face is distorted. On another note, the picture was taken at f2.8 and you can see that the background quickly becomes blurry

Standard lenses are great for portraits as they give a pretty accurate image that’s natural looking and free from distortion.

Telephoto lenses are ideal when you can’t get close to your subject like in a sports arena or on a safari. It’s also great for taking candid shots of people without making them aware that they’re being photographed. Pictures taken on telephotos tend to look 'flat', and a bit more two-dimensional. They compress the background and foreground so that it’s hard to tell how far distances are between objects.

Macro lenses allow you to get very close to your subject to produce images that are life size or larger. Think of close up shots of jewellery and flowers (below).

Zoom versus Prime

Zoom lenses have variable focal lengths, which you select by twisting the lens barrel. Most people are familiar with zoom lenses and you probably got one included when you bought your DSLR. They’re great for re-composing images without having to change lenses and the flexibility makes them convenient to use for all kinds of situations. Typical focal length ranges are given as the minimum and maximum focal length, eg 14-24mm, 18-55mm and 70-200mm.

A prime lens has one focal length only. Common ones are 50mm (also known as a Standard lens), 85mm, 35mm and 300mm. They’re not as convenient to use as zooms because the focal length is fixed, but the quality of them is high as the mechanics of producing them are a lot less complicated than zoom lenses. They’re often considered 'fast', meaning that the apertures on them are large, for example f2.8, f1.8, f1.4, even f1.2, are wonderful for taking pictures in low light. A fantastic fast lens that won’t break the bank is a standard 50mm f1.8 lens, and it's worth having one in your kitbag.

It’s your turn

  1. Take a portrait at various focal lengths without you or the subject moving. Notice the changes in perspective between the objects in the picture and how the subject’s face changes with each different focal length.
  2. Don’t be lazy and use a zoom lens all the time. If you have one, take pictures with a prime lens (or just shoot at the same focal length if you’ve only got a zoom) and force yourself to move your feet. Try different angles.