A zoom lens enables you to use a wide range of focal lengths without having to change lenses, making them very functional indeed. Let’s take a closer look at the different types of zoom lens and their special features. (Reported by Tomoko Suzuki)

 

With just 1 zoom lens, you can create a variety of expressions

Benefits
- Just one lens can cover a wide focal length range
- You don’t have to keep changing your lens

Weaknesses
- Majority of zoom lenses have a large maximum f-number (small maximum aperture)

Zoom lenses are very convenient to use—all you need to do is turn the zoom ring to change the focal length. This saves you the hassle of having to change lenses, which in turn means that you are less likely to miss a shutter opportunity when doing so. It also cuts down the number of lenses you need to carry around, and lighter gear is always a bonus especially when you are travelling, or doing outdoor activities such as hiking. This is why kit lenses are almost always zoom lenses.

The range of focal lengths that a lens can shoot at (its ‘focal range’ or ‘focal length range’) is indicated on the lens. For example, a range of “18-55mm” means that you can change the focal length to anything between (and including) 18mm and 55mm. A shorter focal length gives you a wider angle of view. The longer the focal length, the more it allows you to close in on subjects that are far away.

One thing that you should note is that compared to prime lens, zoom lenses tend to have a bigger maximum f-number (smaller maximum aperture). This means that if you use zoom lenses to shoot in a dimly-lit location, you are more likely to have to use a higher ISO speed. The degree of blurring in the bokeh that you can create with the zoom lens will also be limited, compared to a prime lens capable of a bigger maximum aperture. (We will explain more about bokeh in a future article.)

 

Key concept (1): Types of zoom lenses

There are four types of zoom lenses. Wide angle zoom lenses enable you to capture a wide area of the scene. Standard zoom lenses and superzoom lenses cover a wide range of focal lengths including telephoto ranges. Meanwhile, telephoto zoom lenses enable you to capture close-up images of faraway subjects. All four zoom lens types are available in versions compatible with a full-frame DSLR camera, an APS-C DLSR camera, or an EOS M-series mirrorless camera.

You might be interested in: 
Lens FAQ #9: What is the difference between an f/2.8 and an f/4 telephoto zoom lens?

 

 

Key concept (2): A wide focal range

Zoom lenses are popular with many people because they can cover a wide focal range. For instance, you just need one standard zoom lens to cover an entire range of focal lengths from wide-angle to telephoto. Having such a range allows you to vary the look of your final image, either by to including more of the scene in your frame, or by closing in on a particular area of interest.

For more information, check out:
Photo Effects of Wide Angle Lenses
Professionals Composition Techniques – Making Good Use of Lenses
Utilising the Compression Effect and Large Bokeh of Telephoto Lenses

 

 

 

As the above shows, although the maximum aperture possible is different, the EF24-105mm f/4L IS USM can cover the same focal range as four separate prime lenses.

 

Key concept (3): Variable apertures and fixed apertures

In terms of maximum aperture, zoom lenses fall under either of two categories. On variable aperture lenses, the maximum aperture changes throughout the zoom range, whereas it stays the same on fixed aperture lenses (also known as ‘constant aperture lenses’). The latter allows you to use the same aperture regardless of the focal length used, which is ideal for some situations such as shooting telephoto in low light conditions, where you need as much light to reach the image sensor as possible (also see Key concept 4 below). However, because this involves more sophisticated lens construction, fixed aperture lenses also tend to be larger, heavier and more expensive than variable aperture zoom lenses.

Variable aperture lenses
- EF24-105mm f/3.5-5.6 IS STM 525g
- EF70-300mm f/4-5.6L IS USM 1050g

Fixed aperture lenses
- EF24-70mm f/2.8L II USM 805g
- EF70-200mm f/2.8L IS II USM 1490g

 

Key concept (4): Maximum aperture on variable aperture lenses

The maximum aperture on a variable aperture lens is stated as a range, such as “f/3.5-5.6”. The brighter maximum aperture (smaller f-number) applies at the wide-angle end, and slowly darkens towards the larger f-number as the focal length increases.

Example: On the EF-S18-135mm f/3.5-5.6 IS STM

 

Key concept (5): Maximum aperture and degree of bokeh

In the above example, at the wide-angle of 24mm, the maximum aperture possible is f/3.5 on the variable aperture lens and f/2.8 on the fixed aperture lens. The difference is approximately 1/3 of an f-stop, which may seem tiny but can result in obvious differences in bokeh effect. Note how the background bokeh is more significant in the image shot with the fixed aperture zoom lens.

 

For more about f-stops, check out:
Camera Basics #1: Aperture

You may be also interested in:
Lens FAQ #6: My Zoom Lens Doesn’t Have a Very Bright Maximum Aperture. How Can I Get a Large Bokeh Out of It?

 

In the above example, at the focal length of 70mm (telephoto range), the maximum f-number is f/5.6 on the variable aperture lens, and f/2.8 on the fixed aperture lens—a difference of 2 f-stops. This larger difference has also translated to the bokeh effect—the image by the fixed aperture lens has background bokeh with more significant blurring. If bokeh plays a significant role in your shooting style, you might benefit more from a fixed aperture lens.

 

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