Photography News Issue 31

Photography News | Issue 31 | absolutephoto.com

Technique 55

Photo school Camera class Everyone has to start somewhere, even pros, and in Photo School we look at the core skills every beginner needs. This month, how to shoot a series of focus-stacked images and blend them using software for perfect sharpness…

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Step-by-step Focus stacking

1. Focus on the closest point Using a tripod or other camera support, frame up your composition, giving a little room around the subject to allow for any cropping that might be required during alignment. Next switch to manual focus, either via a switch on the lens or camera body, and activate live view on mode. Zoom in on the screen and find the closest point on the subject you want to be sharpest. Focus there, then take the first shot.

Words & pictures by Kingsley Singleton

Where you focus in the scene affects the depth-of-field created. With this inmind, by focusing in the right spot and using a small aperture, the zone of sharpness can in theory extend from very close to the camera, all the way to infinity. However, in macro shots where you focus close to the camera, this makes depth-of-field harder to extend. And while smaller apertures (higher f/numbers), are required for extended focus, they lead to diffraction; a loss of critical sharpness. So what do you do? Why use focus stacking? One way is to use focus stacking, a technique wherein separate shots are taken and focused at different points throughout the scene, then

combined to produce the ultimate sharpness throughout. This technique also lets you maximise image quality by shooting at the apertures which give the best image quality. So, while shooting normally at f/11 might give the best sharpness but not the greatest depth-of-field, focus stacking separate shots at f/11 will give you both. Not just for macro Focus stacking is most commonly used on macro images where even using the smallest apertures can lack the depth-of-field required to cover the subject. But that’s by no means the end of where it’s useful; it can help on any kind of shot where you want to increase the depth-of-

field and sharpness; a landscape or still-life shot taken with a regular lens for example. Focus stacking is also useful in low-light photography where youmight want to use awider than usual aperture to keep the shutter speed high. Basically, so long as there’s little or no movement in the scene then the pictures should align and stitch together easily. The technique As you’ll see in the step-by-step guide, it’s fairly easy to shoot the separate shots required. The images then need to be blended and any minor shifts in alignment corrected. These shifts are due to the effective focal length of the lens changing by

2. Shift the focus and repeat Again using the magnified view, use the lens’s focusing ring to shift the sharpness slightly further into the scene. To do it accurately, and make sure you don’t miss a bit, make a mental note of where the focus starts to fall away and set the new focus point there. Shoot again, and repeat until you’ve worked through all areas you want to be sharp, front to back. many shots you’ll need to cover the subject. This depends on many things; like the size of the subject and how close you’re focusing. The number of shots required will also rise as you open the aperture and fall as you close it. It’s also important that you don’t miss any ‘slices’ of the subject as you work, so change the focus very slowly. To avoid any sudden loss of sharpness, which can make pics look unnatural, always shoot a few more pictures than you think you might need as a safeguard.

a very small amount as you focus, so the perspective can be altered slightly. Ideally you should expose manually to get consistent lighting and, as focus stacking is all about maximising image sharpness, you don’t want to compromise the clarity with poor technique. Therefore, use your camera’s self timer drive mode and a cable release to avoid camera shake. And switch on any mirror-up or exposure delay modes your camera has to increase sharpness further.

How many shots do you need? The final thing to consider is how

Single image at f/13

25 focus stacked images at f/13

Next month: More camera skills

Focus stacking is one of those techniques with a 50:50 split between shooting and editing, so it’s vital to get both parts right. After shooting the sequence you need to align and blend the pictures, and if you’re working on a landscape or another wide shot where the graduation from sharp to unsharp is simple, this can be done manually, either by masking or erasing the parts that aren’t required. Onmore complex subjects, especially where sharp areas cross over blurred ones, an automated route is best. There’s is a method of automatically aligning, stacking and blending images in Photoshop detailed in the steps on the right, but like many other techniques, if you’re into focus stacking there are dedicated software packages that can offer superior results (see panel far right). Once you’ve blended your image check it closely for any errors, for instance where it goes from sharp to blurred and back again, and reshoot if necessary. Next month: More easy editing tips. Softwareskills Howto stack&blend separate images

1. Stack up the layers The first thing you need to do is stack the shots in layers. With all the pics in Photoshop, go to File>Scripts>Load files into Stack… hit the Add Open Files button, then OK. Once the layered document has been created, you can close the originals. If you’re using Adobe Bridge, highlight the images and go to Tools>Photoshop>Load Files into Photoshop Layers. Or, in Lightroom highlight the images in the Catalogue and go to Photo>Edit In>Open as Layers in Photoshop.

2. Blending the sharpness During stacking, in some versions of Photoshop you’ll get an option called Attempt to Automatically Align Source Images; if so, tick that as it cuts out the next bit. If not, after the images have loaded, make sure the layers are all highlighted (press Ctrl+Alt+A on a PC or Cmd+Alt+A on a Mac) and go to Edit>Auto-Align Layers… then click OK. Next go to Edit>Auto-Blend Layers, select the Stack Images option and click OK. If you’re happy with the blending just go to Layer>Flatten Image and save.

2a. Manual blending If you’re working on a shot where there’s no complicated transition between the separately focused pictures, after alignment you can simply mask or erase the unsharp parts. In the above image, one pic focused in the foreground and the others further into the scene were stacked. Next, a Layer Mask is added to the top layer. Painting black or white hides or reveals the layer, so in this case the foreground (which was out of focus on that layer) is masked away by painting black.

... and what about bespoke focus stacking software? Although you can achieve focus stacking in Photoshop, it makes sense to try packages that have been deliberately designed for the task. These tend to be faster and more accurate than using Photoshop, as well as offering a wide range of options in terms of how the blending is rendered. Check out the excellent Helicon Focus (heliconsoft.com) and Zerene Stacker (zerenesystems.com), both of which are available for around £50 and offer free trials.

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