Photography News Issue 42

Photography News | Issue 42 | absolutephoto.com

Technique 27

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How to decode a wide-angle lens

Front element On a wide-angle lens, the

Filter thread Filter thread size varies from

On some zooms you can use the same maximum aperture at all focal lengths. If the maximum aperture is f/2.8 or wider, these are called ‘fast zooms’. On other zooms the maximum aperture is variable – for example, f/2.8-4 – and you won’t be able to shoot with the same setting at the long end as you can at the short. Variable maximum aperture lenses are often less expensive than constant aperture zooms. Whether you need a fast zoom depends on what kind of light you’ll be working in. A wider maximum aperture lets in more light, allowing you to use faster shutter speeds. Fast wide-angles are important for shooting night landscapes with starry skies or aurora; these fast zooms will be bigger and weightier than those with variable apertures. Using filters on wide lenses One of the prime uses of wide-angle lenses is landscaping, so it’s well worth checking what size filters you’ll need when buying – or if you’ll need an adapter to fit them. Wide lenseswill often need filters as a wider field-of-view usually means more sky and that equates to greater dynamic range. Though many wide-angles have accessory threads allowing you to mount filters and filter holders, some extreme wide-angle lenses have very bulbous front elements and 5 Maximumaperture This states howwide the aperture will open; on wide-angle zooms, the aperture may be variable, closing as you extend the focal length. Wide apertures are useful when exposing and focusing in low-light. Focus distancewindow Here you’ll be able to read the focus distance in metres, and feet, between infinity and the lens’s closest focusing distance. On some wide- angles you’ll also get a depth-of-field scale, helping you judge what’s in focus and what isn’t. 6

Controls Switches here will include

Zoomring On wide-angle zoom lenses, the

front element will often be large and bulbous; and as these lenses focus close to the subject, you should take care not to knock it. Many lenses also have water and oil-repellent coatings, which can make cleaning easier.

model to model, and you’ll need to know this to fit screw-on filters or a filter holders. Some wide-angles, like the Sigma 12-24mmArt pictured above don’t have a filter thread, so a specialist holder must be used.

built in lens hoods that don’t allow conventional filters to fit. You’ll need a special adapter for these models, like Lee Filters’ SW150 system. On very wide lenses, you may find that your regular filter holder becomes visible as vignetting, too. Polarising filters won’t work in the same way as on longer focal lengths, either. To get the maximum effect of a polariser you need to shoot at 90º to the sun, but your wide view may stretch to well over 100º; with so much of the scene covered, the effect will be patchy. Focusing and image stabilisation Arguably, because of their principal uses, wide-angles don’t need to focus all that quickly, or feature image stabilisation. That said, it depends on how you’re intending to use the lens. For instance, if you’re planning to use a 17-40mm, or 16- 35mm handheld as a lens for travel or general photography you might be glad of image stabilisation to sharpen your exposures; camera shake is less noticeable at wide- angle, but it’s better to have stabilisation than not. The extra speed afforded by a focusing motor in the lens, like Sigma’s Hyper Sonic Motor, will help you lock on to fleeting subjects, too. Wide-angles naturally feature closer focusing distances than lenses with longer focal lengths, features like switching fromauto (AF) to manual focus (MF), and activating the image stabilisationmode if the lens has it. Sigma has OS (Optical Stabilisation) technology in its armoury – although it is not featured on this lens. Focal length Onwide-angle zoom lenses, therewill be two focal lengths written here, denoting the widest and longest settings. If it’s a prime, the lens is restricted to a single focal length and you’ll need tomove your feet to reframe. 8

and closer focusing means enlarged detail, but make sure to compare minimum focusing distances to see how close you can go. Distortions and build Some level of barrel distortion (outward bowing lines) used to be part and parcel of wide lenses, but many now claim to feature ‘zero distortion’. The less the lens distorts, the less editing you’ll need to do on the computer, although some softwares do this automatically. Some cameras offer integral correction too. A level of weather sealing is a good thing. Although you should always try to protect the lens in dusty, humid or rainy conditions, weather sealing means you don’t need to worry as much and can continue shooting when other lenses would lose functionality. Top left Sensors smaller than full frame (24x36mm) will crop the view from a lens, so the field of viewwon’t be as wide as you’d think. Here, the main image was shot at 28mm, while the cropped view gives an effective focal length of 42mm. Bottom left Very wide and fisheye lenses can give a highly distorted view. Pictures from them can look amazing when they’re used creatively though. 10 Lensmount The mounting point between lens and camera. Ametal lens mount will offer greater strength and durability, and many lenses have weather sealing here, too, to protect the camera and the lens contacts which transfer exposure and focusing information. zoom ring is used to set the focal length from the from the widest to the longest settings the lens allows. Prime lenses won’t have one of these, of course.

Lens hood A lens hood helps cut out light

Focus ring The focus ring is used to

sources like the sun, which can cause lens flare. They’re particularly useful at wide-angle where the increased field- of-viewmakes it more likely. Lens hood also protect the front element from knocks, and some wide-angles have one built in.

manually focus the lens, and also, in the certain AF modes, to make minor corrections to autofocus.