Sigma 20mm f/1.4 DG HSM Art review: specs and price

The device is protected with extra seals to prevent failures caused by dust, raindrops, and water splashes. Show more

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A metal mount is generally superior to a plastic mount as it is more durable.

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A shorter minimum focal length allows you to get more of the scene in the photo, and offers a wider angle of view than longer focal lengths.

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A longer maximum focal length allows you to focus in on a small part of a scene, and offers a narrower angle of view than shorter focal lengths.

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It comes with a lens hood so that you don’t have to buy it separately. These are used to block strong light sources, such as the sun, from the lens to prevent glare and lens flare.

Optical image stabilization uses gyroscopic sensors to detect the vibrations of the camera. The lens adjusts the optical path accordingly, ensuring that any type of motion blur is corrected before the sensor captures the image. Show more

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The zoom range is the ratio between the longest and shortest focal lengths. A higher zoom range means that the lens is more versatile.

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At the shorter end of the lens you get the widest angle of view. This allows you to fit more of the scene into the photograph (based on APS-C format).

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A true macro lens has a magnification of 1:1. This means that the image produced is a life-size representation of the subject being photographed.

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At the longest end of the lens you get the narrowest angle of view. This allows you to fit a small portion of the scene into the photograph, such as when you are zooming in on a subject (based on APS-C format).

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With a wider aperture the sensor can capture more light, helping to avoid blur by enabling a faster shutter speed. It also provides a shallow depth of field, allowing you to blur the background to focus attention on the subject. Show more

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With a wider aperture the sensor can capture more light, helping to avoid blur by enabling a faster shutter speed. It also provides a shallow depth of field, allowing you to blur the background to focus attention on the subject.

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Similar to the number of aperture blades, rounded blades affect the way the light gets through to the sensor. Rounded blades, often only found on more expensive lenses, improve the appearance of the out-of-focus areas. This allows you to attain better, softer looking bokeh in your photos.

A smaller aperture reduces the amount of light reaching the sensor. This is important in bright conditions where a wider aperture could result in your image being overexposed. Another advantage is that with a smaller aperture you get a greater depth of field, and can keep all of the image in focus.

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The aperture controls how much light gets through to the camera’s sensor. More blades is often an indicator of a better quality lens. It also allows you to achieve much nicer looking bokeh when blurring out your background, whereas a lens with less blades will often produce harsher, more polygonal bokeh.

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A smaller aperture reduces the amount of light reaching the sensor. This is important in bright conditions where a wider aperture could result in your image being overexposed. Another advantage is that with a smaller aperture you get a greater depth of field, and can keep all of the image in focus.

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Lenses with a built-in focus motor can autofocus even if the camera does not have its own focus motor.

Many lenses allow you to focus to infinity. This is essential when you wish to take photos including far off objects, such as when shooting landscapes, in order to make sure everything is sharp and in focus.

Lenses with built-in focus motor focus faster and more quietly than lenses without a focus motor which rely on the camera's body focus motor.

This is the closest distance that the lens can focus. A shorter minimum focus distance allows you to get closer to your subject, and is particularly important when doing macro photography.

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With full-time manual focus, you can move the focus ring whilst it is in AF (autofocus) mode. This means that you can make manual adjustments once the AF has finished, without changing to manual mode.