Photography News Issue 34

Photography News | Issue 34 | absolutephoto.com

Review

Depth-of-fieldexplained

While you are framing the picture, think about what you want sharp within the scene

lens, swapped to the 24mm and moved in close (very!) to get the identical head size, the depth-of-field will be the same. Learning how to use depth-of-field is a key skill so bear the above three factors in mind to start with. Then consider where you focus. Wherever you focus in the scene you get more depth-of-field behind where you have focused than in front of it. So if you’re shooting a landscape with near and distant elements, don’t just focus at infinity and hope the foreground will be sharp. Focus about one third of the distance into the scene so the zone of sharpness extends beyond where you focus and back towards the camera too. To do this, switch to manual focus or use the single AF point to focus at that spot rather than letting the camera decide. While landscapers want a large depth-of-field, portrait workers usually want less, particularly when shooting outdoors where there’s limited control over backgrounds. Positioning the subject so that the background is a little way behind and selecting a wide aperture is the best technique to use, and that way the background’s impact is minimised. You may have noticed that a selling point used by many lens manufacturers is something called ‘bokeh’. This is the effect or look of an out-of-focus background. The effect varies from lens to lens – some lenses give smooth circular highlights, others give more defined octagonal shapes. Lens construction such as the number of diaphragm blades impacts on the shapes you get – the greater the number of blades, the smoother the circles, generally – but so does the actual aperture used and the distance between the subject and the background. If you want to get technical about it, the ideal distance to use for maximum depth-of-field for any given aperture and focal length is called the hyperfocal distance. As most modern lenses don’t have a depth-of-field scale, the easiest way to determine this on location is with a smartphone app such as Depth of Field Calculator (79p) or DOFMaster (£1.49) but there are plenty more available. Many cameras have a depth-of-field preview feature that lets you check how sharp the scene is. Use it and the camera closes the lens aperture to its set value (you normally view the image at the lens’ maximum aperture) and that’s why the viewfinder gets darker – less light is coming through the lens. Let your eye get used to the darker image and you’ll get a better idea of what is sharp within the scene. The preview feature is very much a feature for film cameras where you don’t know what you’ve got until the film is processed. With digital, just take a picture and study it to make sure what you want sharp is sharp.

Depth-of-field is defined as the amount of acceptable sharpness within a picture and, you as the photographer can directly influence howmuch depth-of-field you get with, for instance, your aperture choice. But you should be aware that this influence is not total so, for example, if you want sharpness from 1m to infinity and you have a 200mm telephoto lens set at f/4, you’re just not going to get it. Howmuch or how little depth-of-field you have in a picture has technical considerations, and there are pictorial ones too, so you need to think about the final result. For example, landscape enthusiasts generally like to have a great deal of depth-of-field so everything from near the camera to a distant subject (effectively infinity) is pin-sharp – more on this aspect of depth-of-field very shortly. So, while you’re framing the picture, think about what you want to be sharp within the scene and then set the camera up accordingly bearing this in mind. But as we’ve already mentioned, it might not be possible to achieve the effect you envisage in your mind’s eye. Depth-of-field is affected by three key factors, which are interlinked, so they need to be considered simultaneously when assessing your picture. The lens apertureused The smaller the lens aperture, the greater the depth-of-field. So for landscapes when you want everything sharp from near to far, apertures like f/11 and f/16 are used. In portrait work where you want some separation between the subject and the background, wide lens apertures such as f/4 and f/5.6 are best employed. Camera tosubject distance Depth-of-field, regardless of aperture, lessens as you get closer to the subject. So with macro photography depth-of-field is limited even with small apertures. A 100mmmacro lens at f/16 focused at a subject 30cm away gives depth-of-field of less than 1cm. Focus at 10m and you get depth-of-field from 7m to 12m. The lens focal length Shoot the same subject from the same spot and a wide-angle lens provides a greater depth- of-field than a telephoto lens. A 24mm lens at f/11 focused on a subject 10m from the camera will give you sharpness from 1.5m to infinity, while a 200mm lens at f/11 from the same spot only gives depth-of-field from 9m to 11m. While it’s unlikely you would use lenses in this way, a 24mm and a 200mm produce the same depth-of-field if the image size in the viewfinder, ie. the magnification, is identical. If you took a frame-filling full face portrait with a 200mm

After correction

Above Converging verticals can be corrected in-camera using a perspective control lens, also called tilt and shift lens. Sadly, such lenses are very expensive – the exception is the Samyang T-S 24mm f/3.5 ED AS UMC at £625. If you want one, consider hiring.

Before correction

F/16

F/11

F/8

range of 55-200mm or so. In the 35mm format, this means 70- 200mm or 70-300mm. Many modern telezooms are equipped with image stabilisation to deal with picture-ruining factors such as camera shake. Because you get a greater magnification, it can mean even the slightest camera movement can spoil your pictures. This is what features such as Image Stabilisation (IS) fromCanon, Vibration Reduction (VR) from Nikon and Vibration Compensation (VC) from Tamron are designed to combat. Some brands such as Olympus and Pentax have shake reduction features built into the camera body rather than the lenses. Once you’re equipped with a two-lens outfit you can cover a huge subject range. And it may not be too long before you find that the shortest end of your standard zoom isn’t quite wide enough to cope with interiors or cramped conditions. That’s when your mind will turn to the wide-angle zoom. In the 35mm format this means around 16-35mm, while APS-C users will be looking at a 10-24mm. These lenses are known as ultra wide-angles.

Such lenses do need using with a little care; get in too close to a subject, and you will see some distortion. Try a wide lens on a portrait and you might find the nose is all out of proportion with, say, the ears. The effect can be dramatic so it’s worth using, but you do need to be aware of its potential pitfalls because the effect is not flattering. Wide-angle lenses can also be challenging in that there is toomuch space left around the subject, and the composition looks rather empty. Always check before taking the shot that the composition is as powerful as you canmake it. Use your feet and get in closer if needs be. With your three-lens outfit you are now perfectly equipped to push backyour photographic boundaries. But you should be warned that once you start exploring these lenses further you might find the urge to upgrade irresistible. You might yearn for faster apertures, decide to work with primes or the idea of more specialist optics like macro or perspective control lenses might take hold. One extra lens could be just the beginning of a very exciting lifelong journey.

F/56

F/4

F/2.8

Images These portraits were taken from the same spot with a 70-200mm zoom at 105mm and the focus on the girl was not altered between shots. The only thing changed is the aperture to vary the amount of depth-of-field – the difference is very evident in the background. Of course, adjusting the aperture changes the shutter speed and shooting at smaller apertures means slower shutter speeds. On a bright day this isn’t an issue and on these sunny day shots the shutter speed at f/16 was 1/200sec at ISO 200. On a dull day, a tripod would be needed.