Photography News Issue 30

Technique 115

Photography News Issue 30 absolutephoto.com

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 focusing affects depth-of-field and using High-Pass sharpening

Words & pictures by Kingsley Singleton

In the past few issues we’ve covered lots of ways to improve focusing on a variety of subjects, such as picking the correct AF mode and AF area. But where you focus isn’t just about getting solitary subjects sharp; combined with the aperture setting, it can also have a great effect on a picture’s depth-of-field, so whether you want a landscape with front-to- back sharpness, or a portrait with very shallow focus, it’s good to know. When thinking about depth-of- field, the first place to turn is your aperture setting, or f/number; this controls the size of the aperture in the lens and, for the most part, large apertures (low f/numbers, like f/1.8, f/2.8 or f/4) give a shallow depth-of- field, keeping just as small part of the scene in focus, while small apertures (high f/numbers, like f/16or f/22) keep most of the scene in focus. Then it’s on towhere to focus... 1. Where to focus for the greatest depth-of-field If you’re shooting landscapes or other scenesandwantthepicturetobesharp from the foreground to infinity, you can follow a system called hyperfocal distance focusing. This ensures the maximum depth-of-field at any given aperture, so it helps you keep asmuch sharpness in the scene as possible. The hyperfocal distance is the distance from the camera where you need to focus the lens to achieve the maximum sharpness. The depth-of- field will then extend from that point to infinity, and from half the focused distance back to the camera. The tricky part is calculating it, because the hyperfocal distance changes depending on the sensor size

of your camera, the focal length you’re shooting at and the aperture you’re using. Or rather it would be if there weren’t loads of free apps to do it for you; go get one and try it out. Something to remember is that hyperfocal distance works on a principle of ‘acceptable sharpness’, meaning while the point of focus will always be the sharpest area, objects away from it and within the zone will still be perfectly legible, but might now be tack-sharp. Areas outside of it are deemed unacceptably soft. Therefore, whether you should use the hyperfocal distance depends on the type of scene you’re shooting; if the foreground or background is the most important part, you should still focus there, regardless. And if the background isn’t at infinity (whichwe canpracticallycallthehorizon),thenit may not be required at all. It’s also worth noting that at very small apertures like f/16 or f/22, the depth-of-fieldwill in theorybegreater, but the effects of diffraction (where the light path is disrupted as it passes through the small iris), somewhat negates the effect. 2. Where to focus for the shallowest depth-of-field Just as there’s a point at which depth- of-field is maximised, you can tailor your focusing and composition to produce the shallowest depth-of- field, too. Basically, at a consistent aperture, the closer you focus, the shallower the depth-of-field will appear. So, in practice, if you’re not achieving the shallow focus required, you need to either move towards the subject, or have them come closer to you. Conversely, if you’re struggling

to focus because the depth-of-field is too shallow, you can increase your distance from the subject a little. Again, a depth-of-field calculator app foryourphonewill showyouhow the zone of sharpness gets smaller as you focus closer to the camera, but it’s dependent on sensor size, focal length and aperture. For example, though shooting at a wide aperture like f/2.8 on a typical 85mm portrait lens the depth-of-field is around 2m when focusing on a subject who is 10m away, at 2mdistance from the camera, it shrinks to only 8cm. All lenses have a minimum focusing distance, and you should try toworkalittleawayfromthisasminor movements after focusing could see the focus fall away from where you want it, and ruin the picture. 3. How to shoot without focusing Once you know the relationship between focusing and depth-of-field, you can then apply these effects to improve your shooting speed in situations where focusing is counterproductive ormightmeanyou miss an opportunity. Thisisuseful,whenyou’reshooting candid street and documentary photography where you don’t want to draw attention to yourself, or when you’re shooting moving subjects which at a consistent distance, like the side of a race track. For instance, using a 50mm lens on a full-frame DSLR if you set the aperture to f/11 and the focus ring to about 7m, youwill know that everything from around 3m to 20mwill be in focus. Next month: More essential camera skills explained.

1. Front-to-back sharpness

2. Shallow focus effects

3. Shoot without focusing

Above Focusing can be used to affect the depth-of-field in several ways – a great deal of an aperture’s effect depends on where in the scene the focus falls. In this way you can ensure the greatest depth-of-field or the shallowest. What’s more, learn howmuch of the scene will be in focus at a given distance and aperture, and techniques like panning are easier.

The High-Pass method is a versatile and flexible way of adding sharpness to images in Photoshop or Elements. However, High Pass isn’t an automatic route like Unsharp Mask or Smart Sharpen so you won’t find it under the Filter>Sharpen menu (or Enhance>Sharpen in Elements). It’s instead found by going to the Filter>Other… menu and it involves using Layers and Blending Modes. But give it a try and you might prefer it. High Pass highlights edges in the image, just like Unsharp Mask, so after applying you get what appears to be an image made up of outlines. This is blended with the original to increase edge contrast and add clarity. Because you control how fine these edges are, it can be used to add fine sharpening in some areas, and also change the contrast of the image more widely. As employed here, you can see both methods used on a single image, which allows us to apply a grungy, highly detailed, almost HDR look. Next month: Expert hints & tips for using Smart Sharpen. Softwareskills High-Pass Sharpening

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1. Duplicate the image Open the file to sharpen and copy the picture onto a new layer with Layer>New>Layer via Copy (or Ctrl+J). Now desaturate the layer with Ctrl+Shift+U, which keeps the colours neutral when blended. Next, in the Layers palette (Window>Layers), click where it says Normal and change the new Layer’s Blending Mode to Overlay. In this way, global contrast will be added to the picture, but changing the Blending Mode is vital to adding the High-Pass effect.

2.Add some High Pass Go to Filter>Other>High Pass… and you’ll now be able to set the level of High Pass to be added via the Radius slider. First use the loupe view to find a part of the scene where you can judge the level of sharpening – the focal point is the best bet. Now set the Radius; a low setting creates a tightly controlled effect and restricts the sharpening to fine details; a higher radius gives a more cloudy effect which looks more like a change in midtone contrast.

3. Repeat the effect Here we first added High Pass with a high radius of 20px, to Layer 1, which gives a more contrasty look to the image. Next, Step 1 was repeated, allowing us to add a lower Radius High-Pass effect for a more high-frequency look. Because of the Blending Mode, the two can both be seen, even on separate Layers. Also thanks to Layers, the Opacity can be controlled and it can be masked or deleted where it’s not required. To finish, go to Layer>Flatten Image and save as a new version.

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