by Bob Simpson (One Stop Photo Workshops tutor for the Sunshine Coast)
Most digital images benefit from some post-capture sharpening. Digital camera sensors and lenses always blur an image to some degree and to correct this, photo-software like Photoshop has a range of sharpening options like unsharp mask, smart sharpen and the high pass filter. These tools are great for polishing an image before it is presented to the viewing public, but the path to getting consistently sharp images begins well before we go anywhere near Photoshop. Good camera technique and a knowledge of all the factors that can work against the apparent sharpness of an image are vital if we want to take control and produce the sharpest images we can.
There’s no doubt that expensive, high quality lenses generally have the edge over cheaper models when it comes to sharpness, but the reality is that most of us can’t afford the thousands of dollars it takes to own one of these top-end lenses. But there’s no need to despair – even the relatively cheap kit lenses around today will produce excellent results if they are used to their full potential. You don’t need to break the bank to get consistently sharp, high quality images.
So here, in no particular order, are some capture tips and tricks to help you squeeze that extra bit of sharpness out of your images.
Keep it steady
It’s no secret that a steady hand and/or a stable tripod are important factors in getting sharp images. Setting a fast shutter speed can help overcome the blurring effects of camera-shake but from a creative point of view, we don’t always want to use a fast shutter speed to freeze all motion. And in low light situations, it may not be possible to achieve a good exposure with a fast shutter speed unless you set a very high ISO, which in turn will reduce the quality and apparent sharpness of the image.
There are lots of little tricks to help keep your camera stable and motionless when you’re not using a tripod. If you’re standing up, find a comfortable posture with your feet comfortably apart and elbows tucked into your sides. If possible, brace the camera against a tree, fence-post or some other structure to keep it steady, or consider sitting down or kneeling to reduce the chance of your body swaying. Hold the camera firmly but not tensely, breathe evenly, and practise operating the shutter button with a gentle squeeze or roll of the fingertip. If your lens has image stabilisation or vibration reduction, turn it on. There is an old rule-of-thumb that says the slowest shutter speed you should use when hand-holding a camera is the reciprocal of the focal length of your lens – so for a 50mm focal length, use a shutter speed of at least 1/50th second. This of course depends on a lot of factors, including how good your hand-held technique is, and it is often possible to use a much slower shutter speed if your lens has image stabilisation or vibration reduction.
As a landscape photographer I use a tripod most of the time, but there are still occasions when this alone isn’t enough to ensure a stable platform for my camera. Expensive tripods tend to be more stable than cheaper ones so it is worth buying the best you can afford, and new materials like carbon fibre help to dampen any vibrations that do occur. The risk of vibration increases in windy conditions and when the tripod is standing in moving water, like a flowing stream or at the beach. You can reduce this risk by hanging a heavy weight (like your camera bag) off your tripod, and in windy conditions, by using your body to shield the tripod from gusts. A tripod will also be more prone to vibration the higher it is set, especially if the centre column is raised, so try and keep it set lower if the conditions are less than ideal. In soft substrates like sand and mud, a tripod can slowly sink without you noticing – take some time to push the legs firmly down into the substrate before capturing your image. Image stabilisation or vibration reduction can be counter-productive when your camera is mounted on a tripod so read your camera manual to see what the manufacturers advise. Finally, invest in a cable release or wireless release so you don’t have to touch the camera to fire the shutter – an alternative is to use the self-timer, but a remote release makes it that much easier.
Choose your camera settings wisely
The three camera controls we use to set exposure – shutter speed, aperture and ISO – all play a role in image sharpness. Shutter speed is perhaps the most obvious factor here. As discussed above, a slow shutter speed is more likely to produce an unsharp image than a fast one, although a tripod will overcome this issue in most cases.
But what about the situation where we are photographing a scene that has moving elements in it, like grass swaying in the wind or water tumbling down a cascade? We can just use a fast speed, like 1/1000th second, to freeze all motion but from a creative point of view, this is not always ideal and can make an image look static and lifeless. By using a slower speed, say 1/4 second, the moving elements in a scene will be captured with some degree of blur which helps convey the sense of movement and dynamism in the scene. This approach is particularly effective when an image is composed around the stationary elements of a scene, like rocks and tree-trunks, and there is a strong contrast between the sharpness of these features and the motion-blur of moving elements. This contrast can really highlight the apparent sharpness of the static elements. Many photographers take this approach to extremes by using a strong neutral density filter to produce a very long exposure – say several minutes. In this way, even clouds will be rendered as streaks across the sky, which can create a pleasing, artistic backdrop that further enhances the apparent sharpness of any stationary elements.
The ‘best’ aperture setting (f-stop) for any given scene should be considered from several angles. One of the first things we learn as photographers is that a large, wide-open aperture, like f1.2 (or maybe f4 on some lenses) will create a shallow depth-of-field. This just means that a relatively small part of a scene will be recorded in sharp focus – closer elements and more distant elements will appear out of focus. On the other hand, a small, closed-down aperture, like f16 or f22, will produce a larger depth-of-field so that all parts of a scene, from very close elements to the distant horizon, appear sharp.
So it seems obvious from this that if we want maximum sharpness throughout an image, as is often the case in landscape photography, we just choose the smallest aperture available on our lens and use that. Unfortunately it’s not quite that simple. Most lenses, even very expensive models, don’t retain the same level of sharpness throughout their aperture range – they have an aperture ‘sweet-spot’ that will produce the sharpest possible results. The sweet-spot is usually several f-stops down from the widest aperture setting, often around f8 or f11. Choosing a smaller aperture than this may produce a larger depth-of-field, but sharpness will begin to drop off. This might not be apparent unless you make large prints of your image but it is something to keep in mind. You will find information on the sweet-spot for many lens models with an internet search, and lots of websites explain how to carry out your own tests to determine the sweet spot for your lens.
The ISO setting on digital cameras determines the relative sensitivity (or light-gathering capacity) of the camera sensor. A high setting, say ISO1600, means the sensor becomes very sensitive, and it only takes a small amount of light to properly expose an image. A lower setting, ISO100-200, means the sensor is less sensitive and more light is needed to expose the same image. As we adjust the ISO setting, we also have to vary the shutter speed and/or aperture to allow more or less light to reach the sensor as required.
The problem with choosing a high ISO setting is that it leads to increased digital noise in an image. This is unavoidable in some cases where the only way to achieve a good exposure is to bump up the ISO – a noisy image can be better than no image at all. And there is always the option of using noise reduction software to counter the problem post-capture – that is, or course, if you see it as a problem. A little noise in an image might be to your liking, in the same way that the ‘graininess’ of images captured on film was often deliberately used to create a certain look. But I think it’s fair to say that most current photographers, particularly those who focus on landscapes, would prefer to minimise noise as much as possible most of the time. That is my preference and I always use the lowest ISO setting I can.
As for the relationship between ISO and sharpness, there are some differing views. A common opinion is that a noisy image will appear less sharp than a ‘clean’ one because any fine detail in an image is made less clear and well-defined by the presence of noise. Others say there is no real relationship between ISO and sharpness, and some suggest that a little noise can actually make an image look sharper. I can see where this idea (noise = sharpness) comes from, but it is a gritty sort of sharpness that I prefer to avoid in my landscape images.
There is less argument about the effects of applying post-capture noise reduction to an image – this invariably leads to a softening of fine detail, and if it is applied too heavily will result in an unnatural ‘plastic’ look. As a general rule, I believe that the best path to achieving a high quality, sharp image is to use the lowest ISO possible and avoid the issue of noise altogether.
In the second part of this article, I will look at how focus, filters and other miscellaneous factors can affect the sharpness of our images.