![]() Wide apertures also give decreased depth of field ( i.e. This table lists the common aperture values that are one 'stop' apart: each value lets in twice as much light as the one to its right.Ī lens with a larger maximum aperture allows you to shoot in lower light, and (for example) take pictures indoors without using flash. Confusingly, a smaller number means the lens has a larger maximum aperture – a bigger hole – and therefore can gather more light an F2.8 lens collects twice as much light as an F4, for example. Lens apertures can be expressed in several different ways, with F4, f/4, 1:4 all meaning the same thing. Aperture simply means 'hole' in this context, the hole that lets light pass through the lens and onto your camera's sensor. The aperture specification of a lens describes how much light it is capable of gathering. This means simply that an 18-55mm lens on an APS-C format camera covers the same angle of view as a 28-90mm lens does on a full-frame camera. ![]() These are shown for a full-frame sensor each would cover a smaller area if used with an APS-C or Four Thirds sensor.įor the sake of convenient comparison, lenses are often referred to by their ' 35mm equivalent' focal length for example a 18-55mm kit lens for APS-C may be described as a 28-90mm equivalent. Illustration showing the coverage given by a series of popular focal lengths. As a result, the focal lengths that are useful on one sensor format will differ from those that you'd use for the same purpose on another sensor. The effect is as is as though you've 'zoomed' the lens, but instead you've only magnified a smaller portion of its projected image. The same focal length lenses, mounted on a smaller, APS-C sensor would give a narrower, more cropped-in angle of view, and an even narrower coverage if mounted on a Micro Four Thirds format camera. In this instance it shows the effect of these lenses mounted on a full-frame camera. The image below shows how the angle of view varies with focal length. Here, we can see this lens' key specifications expressed in terms of its focal length span ('zoom range') which is 18-35mm, and its minimum aperture range, which is F3.5 at 18mm, and F4.5 at 35mm. Fixed focal length lenses which don't zoom (also known as ' prime' lenses) just have a single number ( e.g. Zoom lenses are named using two numbers which indicate the extremes of the range, for example 24-70mm for a typical kit zoom lens. The first number used to describe a lens is its focal length in combination with the camera's sensor size, this defines the angle of view covered by the lens, with smaller 'mm' numbers indicating a wider angle or more 'zoomed out' view. We'll look into each of these in more detail below.
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