Sharp Pictures in Five Steps

Sharpness is one of the key tools for drawing viewers’ eyes to pictures and directing the viewer’s attention to different areas. Areas of finely-resolved detail can encourage people’s eyes to focus upon a certain spot or move around the picture as a whole. So it pays to know the factors underpinning image sharpness and how to control them.

Five main factors can make images soft: camera shake, subject motion, poor focusing, use of inappropriate lens aperture and shutter speed settings and image noise. Other factors include the quality of the lenses and whether they are clean and free of smearing and grime.

1. Camera Shake

This problem has been dramatically reduced by image stabilisation, which is almost ubiquitous in consumer digicams and lenses. However, it can still affect image sharpness when cameras are used hand-held, particularly when shooting at slow shutter speeds with long lenses.

The simplest way to prevent camera shake is to mount the camera on a steady tripod and use the self-timer or remote control to trigger the shutter. Locking the mirror up in a DSLR camera removes a tiny residual source of potential vibration and is recommended for exposures longer than about 1/30 second, particularly with close-ups. It provides additional assurance that images will be blur-free.

If you don’t have a tripod, try steadying the camera by holding it against an immobile object, or resting it on a flat surface like a wall, window ledge or table. You may need to increase the camera’s ISO setting because this strategy will probably only work with exposures of one second or less. For longer exposures, a tripod is usually vital.

If you hold the camera correctly, you may be able to use shutter speeds between ¼ and 1/50 second with the camera hand-held. But it takes practice. Keep your elbows well in to your sides and trigger the shutter by pressing the button SLOWLY. Longer lenses should always be cradled in the hand that’s not providing the main support for the camera.  

An 1/8 second exposure taken in very dim lighting with a 24mm lens at f/8 using a Canon EOS 5D II camera, which was steadied against a door frame. The ISO 1600 sensitivity produced almost no image noise because of the high light-capturing ability of the camera’s ‘full frame’ sensor.

2. Subject Motion

It can be difficult to record sharp images of fast-moving subjects, regardless of whether you have stabilisation in your camera or lens. Solving this problem usually requires selecting a fast enough shutter speed to ‘freeze’ the subject’s movement.

Traditionally, photographers favoured a rule of thumb that recommended using the reciprocal of the focal length at which the shot was taken as the minimum shutter speed for hand-holding. While stabilisation will push the odds in your favour, this rule still holds true, although it’s no guarantee of obtaining 100% of sharp shots. Faster shutter speeds will increase the number of sharp shots you obtain.

You may be able to push the odds in your favour by recording a burst of shots, one or more of which may end up sharp. However, unless the camera is held steadily enough and the shutter speed is fast enough, you will probably end up with a collection of images that aren’t quite sharp.

Sometimes a little blurring in parts of the image is desirable. But many subjects lose their impact if even a small part is blurred. The photographer’s skill lies in deciding which treatment to apply for each subject. Subjects moving towards the camera are easier to ‘freeze’ in the frame than subjects moving across the field of view.

Choosing a very fast shutter speed lets you ‘freeze’ rapid movement. Canon EOS 1000D at 100mm focal length, 1/800 second at f/5.6.

Panning the camera in synch with the subject’s motion helps to create a sense of speed by recording some parts of the subject sharply while others are blurred by motion. Canon EOS 1100D with 70-300mm lens at 300mm; 1/150 second at f/6.3; ISO 200.

Panning the camera in synch with the subject’s motion is a useful technique for obtaining sharp images at relatively slow shutter speeds, and almost the only way to capture movement in low light levels without having to use high ISO settings. When done skilfully, use of very slow shutter speeds will blur the background, increasing the sense of subject motion.

Panning takes practice to become proficient. It also requires correct camera holding technique. But when it works, the result can be rewarding.

3. Focusing

Decisions about which areas should appear sharp and how wide the plane of perceived sharpness should be ““ and how to achieve desired results ““ lie at the heart of creative photography. To master the tools for controlling these parameters you must understand how your camera’s AF system works as well as what it can (and can’t) achieve.

Don’t rely totally upon it to produce pictures that are sharp in areas where you want detail resolved because the camera won’t always get it right. Sometimes it will focus on the wrong part of the image; at other times it may not focus at all. It may also track the focus in and out until it finds something to lock onto, delaying the release of the shutter (which may cost you the shot).

Issues that can contribute to this ‘hunting’ for focus include low light levels, low contrast and being too close to your subject. Highly reflective surfaces can also present difficulties. Some cameras will lock the shutter in one or more of these situations and won’t take pictures of subjects that aren’t in focus; others will record indiscriminately.

Learn to use your camera’s AF point selection system (check the instruction manual for details). As a back-up technique, with most cameras you can lock focus (and exposure) by half-pressing the shutter button and keeping it there. Recompose the shot before pressing the shutter button all the way down to take the shot.

Learn when to swap to manual focusing. When photographing people or animals, always focus on the eye that’s closest to you. If the nearest eye is unsharp, the entire shot will appear out-of-focus.

Take time to check which parts of the subject are in focus before pressing the shutter. If your camera has a depth-of-field preview button, holding it down closes the lens aperture allowing you to see what is and isn’t sharp.

When shooting with a wide aperture, the plane of focus can be very shallow and you may need to switch to manual focus mode and/or close the lens aperture a stop or two to ensure the areas you want to record in sharp focus actually appear sharp in the shot. Check again after the shot is taken, using playback zoom to magnify critical areas in the image.

4. Aperture Control

The lens aperture plays a vital role in determining the range of distance within a scene that appears acceptably sharp in the photograph. There is always a transition zone between regions that are sharp and the point where unsharpness becomes obvious. It’s known as the ‘circle of confusion’ and it varies with output size and viewing distance.The plane of acceptable sharpness and the width of the circle of confusion can be controlled by the lens aperture setting. An easy way to remember how aperture settings influence depth of field is that low aperture numbers produce shallow depth of field, while high aperture numbers can make everything in the scene appear sharp.

Depth of field varies with different image sensor sizes plus the effects of the aperture setting and focusing distance. Output viewing size and viewing distance can also influence viewers’ perception of depth of field.

Sometimes you’re forced to use a wide aperture setting because it’s the only way to secure the shot in low light levels. With smaller image sensors, an aperture between f/2.8 and f/4 should produce adequate depth of field for subjects at least two metres from the camera.

Certain lenses, particularly zooms, have ‘sweet spots’ in their aperture ranges that are sharper than others. In most lenses, they are one or two f-stops down from the maximum aperture. Beyond about f/8, many lenses lose sharpness due to the effects of diffraction. Keeping within the sweet spot of the lens can help you to get a little more clarity in your shots.

If the eyes in a portrait are sharp, it may not matter that other features are slightly soft. Canon EOS-1D Mark IV with EF 24-105mm f/4 lens at 82mm focal length, 1/320 second at f/5.6; ISO 6400.

An example of a very shallow depth of field, achieved with the Canon EOS 5D Mark II; 105mm lens at f/4.5 and 1/750 second. The lens is focused on the flower in the foreground, directing the viewer’s attention away from the blurred flowers behind it.

Another photograph from the same camera and lens, but at f/16 to ensure everything in the picture appears sharp; 1/90 second at ISO 200.

5. Image Noise

All digital images combine image information in the form of pixels plus the background electronic noise associated with all digital equipment. When the ratio of signal (image information) to noise is high, images should appear sharp if all other parameters are recorded satisfactorily.

As the proportion of noise rises, the noise becomes visible as granularity and develops into scattered spots of different colours, finally progressing into blotchiness and a noticeable loss of sharpness. The relative sizes of the image sensor and the camera’s megapixel count are the main determinants of apparent noise levels.

The more light each photosite in the sensor can collect, the less it is likely to be noise-affected. Large sensors with relatively low megapixel counts provide the optimum conditions for recording images with high signal-to-noise ratios (i.e. sharp images).

Increasing the camera’s ISO setting boosts the image signal but also amplifies the amount of noise in the image. The stronger the image signal the more it can tolerate higher ISO settings.

For example, the noise level produced by a M4/3 camera’s sensor at ISO 800 is roughly equivalent to that produced by a ‘full frame’ sensor (which has roughly four times its area) at ISO 3200. A digicam with a 1/2.5-inch sensor (which has roughly 1/16 the area) will contain equivalent noise levels at ISO 100.

You can use a small-sensor digicam to take sharp pictures with little or no visible noise if you shoot with low ISO settings (ISO 200 or lower with most digicams). But if you want relatively noise-free images at low light levels, you really need a DSLR camera.

Regardless of the size of their sensors, most cameras include noise-reduction processing ““ and many apply it by default at ISO settings of 400 or higher. Unfortunately, no processing algorithm performs perfectly, so there will be trade-offs between noise removal and preservation of fine, low-contrast detail. Image sharpness can be sacrificed.

Some cameras let you adjust the maximum ISO level for the Auto ISO mode. This enables you to allow the camera to adjust sensitivity according to the shooting conditions without straying into sensitivity levels that could produce visible noise. It’s a valuable tool once you’ve determined the limitations of your camera’s sensor.

An early morning shot in low light levels taken with the Panasonic DMC-G5 and Lumix G X Vario 12-35mm f/2.8 ASPH. POWER OIS lens set at 12mm, with an aperture of f/3.2 at 1/160 second and ISO 160.

A six-second exposure at f/16 with the Panasonic DMC-G5 mounted on a tripod. Lumix G X Vario PZ 14-42mm/F3.5-5.6 ASPH./POWER OIS lens at 22mm focal length; ISO 160.

Stabilisation

Whether they’re in the camera body or lens, image stabilisation (IS) systems are an important aid to sharp photos. Lens-based IS systems are slightly more effective and provide better corrections for close-up shooting. Although seldom included in wide-angle lenses, they are desirable in any lens with a focal length longer than about 85mm.

Body-integrated IS works with any lens, and you can simply upgrade the camera body as stabilisation systems are improved, without having to replace an entire suite of lenses. These systems are also better at correcting the roll rotation produced when the shutter button is pressed rapidly.

However, in body-integrated IS, the image projected to the phase-detection autofocus system isn’t stabilised, which can reduce AF speeds. And in cameras that use optical viewfinders, you can’t see the effects of the stabilisation. (Cameras with EVFs don’t have this problem.)

Body-integrated systems also require the lens to have a larger output image circle because the sensor is moved during exposure. These systems are less suitable for extreme telephoto lenses but can provide steadying for wide and ultra-wide angle lenses, which often lack stabilisation entirely.

Both systems draw power from the camera’s battery. It’s seldom a large drain but, in situations where power management is critical, it can be worthwhile switching stabilisation off when it’s not required, such as when the camera is tripod mounted.

Excellent in-camera stabilisation was vital for this shot taken with the Panasonic DMC-FZ200 at the maximum optical zoom of 108mm plus 2x digital zoom (equivalent to 1200mm in 35mm format); 1/320 second at f/4.

Deliberate Blurring

Photographers often use blurring to achieve a sensation of movement in their pictures. The use of slow shutter speeds to record moving water is so common it’s almost a clichø©. But it remains a popular technique.

The camera must be mounted on a tripod and, ideally, the exposure should be triggered with the self-timer or a remote control. The longer the exposure the more blurred and ‘milky looking’ the water appears.

 

This is an excerpt from Photo Review Issue 54.

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