What is maximum aperture? It’s a question we often hear from new photographers who are getting to grips with their lenses or trying to understand depth of field. In this guide we explain what it means to set the maximum aperture, which lenses go widest and what you actually gain in terms of your images.
The aperture setting of the lens controls the amount of light that passes through, so you can use this setting as part of your exposure adjustments.
In dim light you can use a wider lens aperture so that more of the light gets through to reach the sensor, and in bright light you can use a smaller lens aperture to reduce the intensity.
There are other exposure adjustments too, of course, including the shutter speed, or exposure time, and the ISO, or sensitivity setting of the sensor.
In practice you adjust all three – aperture, shutter speed and ISO – according to the conditions and the type of subject you’re shooting.
However, if the lens lets through more light, you can use a faster shutter speed, which means you can freeze fast-moving action more easily, or shoot in lower light without risking camera shake from slow shutter speeds.
Without that, your only alternative would be to increase the ISO setting, which increases the digital noise in your pictures.
The lens aperture also has an effect on the depth of field, or near-to-far sharpness in your pictures. The wider the aperture, the shallower the depth of field.
For landscape photography and close-ups, extra-wide apertures are less important, because you generally want as much depth of field as you can get.
For portraits and sports photography, however, it’s much better if you can blur the background so that your subject stands out more clearly – and that’s where a wide maximum aperture is important.
This is why so-called ‘portrait’ lenses and professional telephotos have wide maximum apertures. They are more expensive, but they give the special shallow depth of field effects that professionals look for.
Maximum Aperture: key points to know
■ Lens aperture values follow a fixed sequence of values from f/16 to f/11 to f/8 and so on. Your DSLR can also set intermediate values, which we’ve shown above in smaller text between the main ones.
■ Professional-quality lenses usually offer wider maximum apertures than cheaper ‘consumer’ lenses – even lenses of the same focal length.
■ Professional zooms usually have constant maximum apertures through the zoom range
■ Cheaper ‘consumer’ zoom lenses will usually have a lower maximum aperture at full zoom than at their shortest length.
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