Getting a sharp image may sound simple enough given all the technology in your EOS camera. However, there's a lot to think about if you want the best results. There are a number of camera settings that can affect image sharpness. If you are not getting super-sharp images the reasons can be many and varied. We explore the causes and solutions.
Shutter speed choice
There are two possible reasons for blurred images as far as shutter speed is concerned – that it isn't fast enough to freeze your moving subject – see our guide to suitable shutter speeds for action photography – or because you're shooting handheld and your shutter speed isn't fast enough for the lens you're using.
Camera movement during the exposure is the number one cause of blurred images. If you are shooting handheld, the rule of thumb is that the shutter speed needs to be at least 1/focal length.
This is easy with a fixed focal length lens. For example, set 1/100 second or faster with a 100mm lens. However, if you are shooting with a 70-200mm lens you need a shutter speed of 1/70 second or faster at the 70mm end of the zoom, but 1/200 second at the 200mm setting.
In some instances, your choice of shooting mode can take away the pressure of setting the correct shutter speed for handholding.
Shutter-priority (Tv) mode lets you set a suitable shutter speed for the lens focal length, leaving the camera to choose the aperture for correct exposure.
Program mode senses the lens focal length, including zoom settings, and sets a suitable shutter speed (providing the ISO is on Auto or set high enough to allow this) so as to prevent blur from camera shake.
Aperture-priority (Av) mode is a common cause of blurred images, so make sure you check the shutter speed that's been chosen by the camera. Again, if ISO is on Auto, then the camera will aim to set a fast enough shutter speed.
Image sharpness is not consistent all the way through the aperture range of a lens. Edge definition at the widest aperture can be soft. There is usually a significant improvement as you stop down, with the best results from many lenses at around f8 or f11. This is known as the ‘sweet spot’. As you continue to stop the lens down, the overall performance deteriorates again as you progress towards its smallest aperture.
The lowest quality setting is normally the smallest aperture – usually f22 or f32. This is caused by diffraction. The exceptions to this rule are macro lenses which are designed to work at the smaller apertures.
Above These images (cropped) were taken with the EF-S 18-55mm f3.5-5.6 USM kit lens supplied with many of the more affordable EOS cameras. The lens can give very good images, but the quality varies with the selected aperture. Wide open it is surprisingly good and improves as you stop down to f8 and f11. However, the sharpness starts to decline at f16 and becomes quite poor when the lens is used with an aperture of f22.
There is less deterioration with more expensive lenses since more corrective lenses and coatings are built into the lens to compensate for the softening that occurs. As a result, these lenses are larger and heavier. Fixed focal length lenses generally give the most consistent quality as with only the one focal length they are easier to design and correct.
The Picture Style feature in your EOS camera is responsible for adjusting four parameters, which are normally thought of as being post-production controls. These are sharpness, contrast, saturation and colour tone.
If you shoot RAW images all these adjustments can be made using suitable imaging software on your computer. The Picture Style information set on the camera is stored as metadata with the image file, but the settings can be overridden. This is easy with Canon’s Digital Photo Professional (DPP) software.
If you shoot JPEG files, it is possible to make adjustments using imaging software, but it is a lot easier to let the camera do the processing for you through the Picture Style settings.
All digital images need to be sharpened at some stage. This is because digital cameras use a dichroic filter in front of the imaging sensor to diffuse the image, reducing an effect called moiré (unwanted patterns which can occur when there are very fine lines in fabrics such as silk). However, this filter causes a slight softening of the image.
Historically, sharpening was always done as the very last stage in the image processing. That's because the relatively small number of pixels used in the early days of digital needed to be increased if a large print was required. This process, called interpolation, creates new pixel points in the image, basing their values on the data from adjacent pixels. If the image is sharpened before interpolation takes place it makes the sharpening heavier and the images appear over-sharpened.
Today, camera sensors have between 18 and 50 million pixels. These can produce the commonly-used print sizes without any interpolation. This means that it is acceptable to sharpen the image in-camera.
Sharpening is controlled by the selected Picture Style. Most of the Picture Styles automatically sharpen the image. However, the Neutral and Faithful Picture Styles leave the image unsharpened. These Picture Styles are intended for users who prefer to make all the adjustments themselves.
It might appear that the Neutral and Faithful options are identical. However, there is more to Picture Styles than meets the eye. Landscape, for example, produces punchier greens and blues, while Portrait optimises skin colour tones. Faithful aims to produce colours close to those of the subject. Neutral has lower contrast and saturation, suitable for images which will be post-processed.
Fixing the camera to a tripod is an obvious way to reduce camera shake. However, with fast shutter speeds (courtesy of high ISO values) and image stabilisation lenses, tripods are less essential than they were in the early days of photography.
Some landscape photographers use them because they like to take time composing an image, or like to use slow shutter speeds with a small aperture.
If you do a lot of macro photography a tripod is recommended because the effects of camera shake are magnified at close distances. Alternatively, shoot with flash – the brief illumination (less than 1/1000 second) is enough the freeze any movement of the camera. It will also freeze the movement of a sprightly subject.
Where did the camera focus?
When on autofocus, the camera will always try to focus on the area of the subject closest to the camera, using the active focusing points (how many depends on your camera and which focusing area/method you're using). This is to prevent the camera focusing on the background and leaving the foreground subject out of focus.
This can cause problems when you want the focus to be on part of the subject which is not the closest point to the camera. In portrait photography for example, you want the camera focused on the eyes of the subject, not the nose. That’s why some portrait photographers resort to manual focusing, where they have total control.
If you shoot RAW image files, you can check which AF points were used by the camera. Open Canon’s Digital Photo Professional (DPP) software and go to Tools > AF point display settings (DPP 4).
Having all the focusing points active can be great when shooting subjects that are moving – it makes it much easier for the camera to track the subject. However, when shooting static subjects we normally recommend using a single focusing point and aiming it at the area of the subject you want to be in focus. You can lock the focus by partially depressing the shutter button and then re-framing the image, if required, before taking the image.
At smaller lens apertures, depth-of-field might give acceptable sharpness to part of the subject, but pin-sharpness will only occur at the focused distance. If the subject is spread out, as in a landscape, you will have to rely on depth-of-field. Focus one-third of the way into the scene for maximum acceptable sharpness.
Canon manufactures a range of image stabilisation (IS) lenses which can help you to reduce the effects of camera shake when holding a camera in your hands.
With a non-IS lens, moving the camera shifts the image across the digital sensor. Even slight movement of the camera blurs the image.
If you use an IS lens, camera shake is detected by two gyro sensors in the lens – one for pitch and one for yaw. The sensors measure both the speed and angle of the movement. This data is passed to a microcomputer which instructs a special group of elements within the lens to move at right angles to the lens axis. The amount and direction of this movement is calculated to counteract the amount and direction of the camera movement. The result is that the image on the sensor does not move, despite the camera movement.
Canon’s image stabilisation system copes with the vibrations of a moving vehicle, boat or even a helicopter. However, for most of us the fact that it will overcome the movement of our hands is the main advantage.
The effectiveness of an IS lens is usually quoted in terms of stops. A lens which gives a 4-stop advantage means that you can expect similar sharpness with an IS lens at 1/15 second to the same lens without IS at 1/250 second. Our advice is not to push IS lenses to their limits, but use them as just a part of your campaign for sharper images.
This is what happens when you try to shoot with a hand-held camera and a telephoto lens at a slow shutter speed. Movement of the camera (i.e. camera shake) during the exposure has blurred the image. Steadying the camera on a tripod is not recommended in busy cities. EOS 650D, EF 70-300mm f4-5.6L IS USM lens at 300mm, 1/40 second at f5.6, ISO 1600.
This shot was taken immediately afterwards, but with the image stabilisation switched on. The EF 70-300mm f4-5.6L IS USM lens offers up to 4 stops IS correction, so shooting at 1/40 second using IS gives the effect of shooting at 1/640 second, fast enough to overcome effects of camera shake with a 300mm lens. EOS 650D, EF 70-300mm f4-5.6L IS USM lens at 300mm, 1/40 second at f5.6, ISO 1600.