by Bob Simpson (One Stop Photo Workshops tutor for the Sunshine Coast)
Nail the focus
Accurate focusing is fundamental to achieving sharp images….no surprises there! A common selling-point for new camera models is the promise of better and faster auto-focus, with more AF sensor points, new focus-tracking modes, and improved AF performance in low light. As clever as these advancements are, and as useful as they are in certain scenarios, for most landscape photography I’d recommend turning off the AF functions and learning how to manually focus your lenses.
The thing with landscape photography is that we often want to keep the whole image, from close foreground to distant horizon, in sharp focus. So rather than focusing on any particular object in the scene, the aim is to maximise the depth of field so that all objects in the scene appear sharp. An old rule of thumb to achieve this is to set a wide aperture, say f16, and focus one-third of the way into the scene. This usually works okay with a wide-angle lens but it can be hit-and-miss in a lot of cases, especially as you move to longer focal lengths.
A more precise way of working out where to set your focus is to use the hyperfocal distance. By focusing at the hyperfocal distance, everything in a scene from half of the hyperfocal distance to the horizon will appear acceptably sharp. The hyperfocal distance is different for every combination of focal length and aperture, but you don’t need to memorise these things or be a mathematician to work them out – hyperfocal distance charts and apps are readily available online so you can either download one and keep it in your pocket or just refer to your smartphone. I carry a small laminated chart for each of my lenses in my top pocket every time I go out.
As an example, the hyperfocal distance for a 17mm lens (on a full-frame DSLR) with the aperture set at f11 is approximately one metre. This tells you that by setting your 17mm lens to f11 and focussing at one metre, everything in the image from a distance of 0.5 metres (half the hyperfocal distance) to the far distance will appear acceptably sharp. You can check this using the depth-of-field preview, if your camera has one, or by zooming into a captured image on the LCD screen.
While this method works fine in most cases, there are techniques available to take the matter further and achieve virtually unlimited depth-of-field at any aperture or focal length. Focus-stacking is a process of taking multiple images with the focus set at a slightly different position in each, and then combining the sharpest bits of each image into a single, final result. This method is especially popular in macro photography where the depth-of-field is often so narrow that it would be impossible to get the whole subject in focus with a single image. So a series of images are captured at different focus settings and then bundled into a program like Helicon Focus, Zerene Stacker, or Photoshop for automatic blending.
Focus-stacking can also be used to expand the depth-of-field in landscape photographs. I’ve found it useful when shooting with longer focal lengths where hyperfocal focusing won’t produce the depth-of-field I want to achieve. Often in these cases, only two or three images at different focus settings are needed to ensure everything is sharp from front to back, and these can be easily blended together manually using layers and masks.
It isn’t always the case that we want our landscape images to be sharp from front to back. A wide aperture can be selected to minimise the depth-of-field so that only the portion of the image that we want to highlight is in sharp focus and the rest is blurred. In this case, precise focus on the main subject is required. Auto-focus can do a good job here, but for full control, I’d recommend using manual focus in conjunction with the liveview LCD screen – just zoom in to the part of the image where accurate focus is most critical and adjust the focus-ring as needed.
I’ve run through some of the most important factors that can affect image sharpness but the story doesn’t stop there. Below is a list of other tips to keep in mind to help maximise image quality and sharpness.
Use good quality filters
A filter placed over the front element of your lens has the potential to reduce image quality and sharpness. Higher quality (and more expensive) filters are engineered to precise standards and include coatings to minimise lens flare and other aberrations, so it’s worth buying the best filters you can afford. The risk of reduced image quality increases if you stack filters together, especially if they are not kept spotlessly clean, and when shooting directly towards a light source.
Use a lens hood
Lens flare occurs when strong light enters the lens and is reflected around by the internal lens elements before it hits the sensor. It is a common problem in landscape photography when shooting towards the sun and will often show up in images as colourful polygonal shapes or washed-out areas of reduced contrast. To avoid it, you need to keep direct sunlight off the front element of your lens and one way to do that is to attach a lens hood. Unfortunately, with wide angle lenses a lens hood can’t extend too far out from the front of the lens or it will cause vignetting so its effectiveness is limited. You can overcome this by using your hand or some other object to shade the lens while an exposure is made – just make sure to keep your hand out of frame. Of course, a lens hood (or your hand) isn’t much use when shooting directly towards the sun, but there are other ways of minimising flare in these situations – but that will have to wait for another article!
Think about distance from subject
Objects that are close to the camera will invariably appear sharper and more detailed than those that are far away. The light that reaches us from a distant object has been diffused and deflected as it passes through the atmosphere so the distant object will often appear hazy, less clear, and less sharp than a close one. This is a simple fact that is easily understood and experienced by all of us on a daily basis – we expect distant objects to appear less contrasty and well-defined. It’s worth keeping this in mind when processing an image and resisting the temptation to add too much contrast or sharpening to distant objects. A natural graduation of contrast, decreasing from the foreground to the background, adds a sense of depth to an image.
Don’t zoom to extremes
In many zoom lenses, image sharpness and quality tend to fall away at the extremes of the zoom range. You will often find the focal ‘sweet spot’ of a lens is somewhere in the middle of the zoom range, so it can pay to back off a little from the widest focal length or the longest telephoto setting.
Take multiple shots
A good insurance policy to employ when photographing in strong winds, or any other situation where there is a high risk of camera-shake, is to take multiple shots of a scene in the hope of getting at least one sharp one. The LCD screen on your camera allows you to review an image for sharpness after each shot, but small amounts of blur might not be obvious until you get home and view the image large on a computer screen. Taking a few extra shots costs nothing and could mean the difference between bringing home a keeper and having to discard your morning’s work because it’s all blurred.
Keep everything clean
And a simple common-sense rule to finish – start each session with a well-cleaned lens and filters, and make sure they stay that way throughout the session. Always carry several clean microfibre cloths, and maybe some lens cleaning fluid or a LensPen for more persistent grime. A greasy thumb-print on your ND filter will result in a blurry patch in your image that can’t be easily fixed with processing, if it can be fixed at all. Windy days at the beach are especially problematic when fine salt-mist can settle on all surfaces, including the front element of your lens. Wiping this with a cloth will just spread the salt around, so a small dose of lens cleaning fluid is sometimes needed to restore a sparkling, clean finish.