All about focal length and lenses

January 16, 2023

This is part of a series of articles dealing with the fundamental technical aspects of using a DSLR or mirrorless camera.

One of the overwhelming things about getting an interchangeable lens camera is the number of lens choices you have. In this article, we’ll do a rundown on focal lengths and lens properties, as well as their applications in photography.

Most entry-level and many intermediate level cameras will come with a basic zoom lens, which is suitable for someone starting out in photography and to allow them to find their niche.

Once you’ve found your niche, you’ll no doubt want to acquire lenses that best suit this niche. This is where the choice can be overwhelming.

Prime vs zoom lenses

You’ve probably come across the term ‘prime lens’ and thought that such lenses are innately better than ‘non-prime’ lenses.

Not necessarily so. A prime lens is simply a lens that is of a fixed focal length – i.e. a lens that doesn’t zoom in and out. The opposite of a prime lens is a zoom lens.

With that being said, a fixed focal length lens and zoom lenses both have advantages and disadvantages.

With zoom lenses, you have the advantage of convenience, as you can cover a range of focal lengths without having to swap lenses.

As such, for example, a zoom lens is good for photojournalism as it gives the photographer easy access to different focal lengths, and where time spent changing lenses may mean the photographer misses a newsworthy moment in a fast paced situation.

However, with this convenience comes a generally hefty price tag (particularly for higher-end zoom lenses) as such lenses require more moving parts and the need to compensate for a focal range. As a result of this, image distortion at the extreme ends of their focal range range, particularly for cheaper zoom lenses, can be an issue.

Fixed focal length lenses are manufactured specifically for that focal length – they have less moving parts which means they’ll perform better than a zoom lens at the equivalent focal length, and are generally lighter and less expensive than zooms at their equivalent price point. Fixed focal length lenses also generally have a bigger maximum aperture.

Of course, you don’t get the same convenience as you need to carry more gear to get the same focal range.

As to whether you go for zoom lenses or prime lenses, or a combination of both, depends entirely on your specialty.

Reading the numbers

First of all, on the lens itself, generally on the front or on the side of the lens, you’ll see a few numbers which will be common across all lens manufacturers:

These numbers are as follows:

  1. The focal length. On a fixed focal length lens, this will be a single number. On a zoom lens, this will be a range, i.e. 70-200.
  2. Maximum aperture. The maximum aperture of a lens can be fixed or, in the case of some zoom lenses, variable. For example, a variable aperture lens with 3.5-4.5 means that at its widest focal length, the maximum aperture will be 3.5. When the lens is zoomed all the way in, the maximum aperture decreases to 4.5. The maximum aperture changes as the lens is zoomed in and out.
  3. Filter diameter. Measured in millimeters. Most lenses allow you to attach filters to the front of them, such as circular polariser or neutral density filters. The filter size needs to match the number printed on the lens if it is to fit.

Common focal lengths and their uses

The focal length of the lens, to put it simply, determines how magnified the image is relative to your position. Focal length also determines the field of view.

Focal lengths also determine how close objects in an image appear relative to each other.

For example, with wide angle focal lengths – the background in an image will appear further away from the foreground. With longer focal lengths, with the photographer standing in the same position, the background of an image will appear closer to the foreground.

Different focal lengths have different intended uses. These are as follows:

Super wide: 14mm, 16mm, 20mm – best for capturing landscapes due to being capable of capturing wide scenes.

Standard Wide: 24mm, 28mm – a standard wide angle that is suitable for both landscapes as well as close up/dramatic action shots at events.

Wide Normal: 35mm, 40mm – Suitable for portraits where a greater deal of context is desired in the image. Also good for group portraits as they still capture a good wide view.

Normal: 50mm – suitable for portraits and everyday shooting due to their being close to what the human eye can see.

Telephoto: 85mm, 100mm 135mm – best for portraits due to the pleasing background defocus (bokeh) they produce at bigger apertures, as well as their compression effect.

Super Telephoto: 200mm, 300mm, 500mm, 600mm – best for shooting subjects from a distance, such as sports, wild animals, etc.

Specialty lenses

In addition to the range of focal lengths, lenses are produced to cater to specific niches or interests, as well as to extend the capability of existing lenses without having to purchase a new lens.

Macro Lenses – these lenses allow the photographer to shoot subjects in detail at a lifelike 1:1 ratio. They generally come in 50mm and 100mm variants though variants at either end of these focal lengths exist with some manufacturers. Due to their capabilities in capturing small things in detail, they are excellent for photographing insects and other small subject matter.

Fish Eye Lenses – Fish-eye lenses are becoming less common, and usually come in the form of lens adapters that fit a manufacturer’s widest angle lenses. Where they are available, they generally come in 8mm to 16mm variations and are noted for their distortion and wide angle (typically 180 degree or more) of view.

Teleconverters – these attach to the lens mount, which in turn attach to the camera. They generally come in 1.3x, 1.5x and 2x variants, meaning they increase the maximum focal length of the lens they attach to. Teleconverters are generally only compatible with a limited number of lenses, generally longer and high-end telephoto lenses, within the manufacturer’s range.

Note that a teleconverter will also decrease the maximum aperture of the lens. A 2x teleconverter, for example, will decrease the maximum aperture of the lens by 2 stops. See the what is aperture in photography article for more information on stops.

That covers the basics of lenses. So far in this series of articles, we’ve covered Aperture, as well as Shutter Speed. Articles in the coming days and weeks will cover other aspects of photography and camera operation.

Matt Hrkac

Matt Hrkac is a photographer and photojournalist based in Geelong and works across Melbourne and throughout Victoria.


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