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Amateur Photographer

ABSOLUTE SHARPNESS

Use Live View to focus on different points in the scene, starting at the bottom of the frame
Derelict barn at The Roaches in the Peak District (Staffordshire) Nikon D610, 16-35mm, 3sec at f/18, ISO 100

Sharpness and depth-of-field, or indeed a lack of it when shooting some subjects, have long been a creative way of controlling what the viewers of images are drawn to. And for the majority of landscapes, a large depth-of-field with front-to-back sharpness is often preferable. The only problem is, it’s not always possible to get everything in focus; some parts of the scene will be pin-sharp while others, usually the background, will be ‘acceptably sharp’, and that’s where focus stacking comes in.

Focus stacking makes images look hyperreal because the results are much sharper than a single exposure at f/11 or f/16, and the depth-of-field offers pin-sharpness throughout the scene. The human eye certainly cannot resolve this level of detail and sharpness, and is one of the many reasons why this is such a compelling technique. So compelling in fact, that it’s even safe to say it’s addictive: once you stack, there’s no going back!

How to shoot focus-stacked images

Focus stacking requires you to shoot between three and five images of a scene, on average, with each focused at a different point in the scene. This ensures that absolute sharpness is achieved at all distances between the camera and the background, and just like shooting a panoramic image you have to make sure that in each shot the depth-of-field overlaps half of the previous shot and the next one. These images are then blended together in Photoshop.

When shooting stacked images, everything is exactly the same as shooting a single image of a scene; you use the same settings, ideally aperture-priority or manual mode, and filters as required to control exposure. The two main differences are that you shoot at either f/8 or f/11 to take advantage of the lens’ sweet spot (see below), and you take a number of images at different focus distances. The easiest way to focus is to shoot in Live View, using the on-screen focus point to set the point of focus for each shot. Start at the bottom of the frame and move up the screen to capture an image at each of the main depths/distances within the scene. Don’t forget to overlap the in-focus areas in each shot to ensure that sharpness is captured throughout the scene across three to five images.

When to focus stack

Like any technique there’s a time and place for focus stacking, so use your judgement to avoid unnecessary editing and a hard drive full of image files. The basic test is whether or not the foreground interest is close to the camera or if the detail in the foreground and background are equally important and both need to be pin-sharp. You also need to ask yourself if you’ll be making a large print of the image? For many wider scenes where the foreground interest is a couple of metres away from the camera you can often get away with shooting at f/11-f/16 on a full-frame camera, or f/8- f/11 on APS-C. These settings provide sufficient overall image sharpness and depth-of-field for the respective camera formats.

Beyond acceptable sharpness

Acceptable sharpness is a term that’s used to describe areas of an image that are in focus, but they are not as sharp as the area surrounding the actual point of focus. As the name suggests, this type of sharpness is deemed acceptable by most, and for the majority of landscape images, this occurs at the bottom of the frame or right at the back of the scene – so not necessarily prominent parts of the image. For scenes where the foreground is close to the camera and the background much further back, this phenomenon is accentuated and makes a strong case for using focus stacking to ensure sharpness throughout.

The sweet spot

This is the point where the lens is able to resolve detail at its sharpest before diffraction becomes an issue and results in an overall softening of images. The sweet spot of lenses most often sits in the middle of the aperture range, so f/8 or f/11.

This can sometimes be confusing because when you say, ‘the point a lens is at its sharpest’, it’s not uncommon for people to think that this statement relates to depth-of-field. Depth-of-field is obviously larger at f/22 than it is at f/8, but overall image sharpness at f/8 is noticeably sharper than that at f/22.

Focus stacking is all about taking advantage of the best image quality your lens can offer, and while sweet spot apertures don’t provide the largest depth-of-field, the process allows you to achieve a depth-of-field and level of sharpness far in excess of that which is possible at f/16 or f/22.

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