22/12/2023
Does maximum aperture matter?
You pay more for ‘fast’ lenses – but do you really need the speed?
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The maximum aperture in the lens description can be an important consideration when you’re looking for a new prime or zoom. Some zoom lenses have a range of apertures instead of a single aperture. This means that the maximum aperture gets smaller as you zoom. The Canon RF 24-105mm F4L IS USM offers a constant f/4 maximum aperture throughout the zoom range for example, whereas the maximum aperture on the cheaper RF 24-105mm F4-7.1 IS STM decreases from f/4 at 24mm to only f/7.1 at 105mm.
The larger the maximum aperture, the more light it’s capable of letting into the camera – and the more light you have available, the faster the shutter speed can be. That’s why lenses with large maximum apertures are often described as being ‘fast’. A larger aperture makes it easier to shoot in low light or freeze action without having to push up the ISO too high. Fast maximum apertures also make it easier to achieve shallow depth of field effects. There are a number of other factors that affect the depth of field, including the distance you are from the subject, but opening the aperture wide is a simple way to make the subject stand out against a blurred background. If you shoot landscapes or other subjects where you need lots of depth of field, small maximum apertures are less of an issue.
The RF mount has been a game-changer when it comes to maximum aperture. The ability to autofocus at apertures as small as f/22 has opened up new opportunities for lens design. Take the RF 800mm F11 IS STM super-telephoto lens; thanks to its smaller maximum aperture, it’s more compact, lightweight and affordable than the RF 800mm F5.6L IS USM. Attach a 2x extender and it becomes a 1600mm f/22 lens with usable AF.
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Shooting for bokeh
A large maximum aperture, such as f/2.8 used here, gives you more freedom to explore shallow depth of field effects ■