Photography News issue 27

Photography News Issue 27

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, which AF Mode and AF Area to choose and how sharpening works in Photoshop

Picking an AF mode There are two core AF modes, single (also called one-shot) and continuous (servo). These are located using an AF button on the camera body, or via a menu. Some cameras have a third (AF auto) that switches between the two depending on the subject. Single/one-shot AF mode is used for static or slow-moving subjects where you have time to perfect the focus, like a landscape or a posed portrait. In single AF, when focus is achieved it is locked and you’ll need to refocus if the subject moves. This mode alsousually requires focus tobe locked before a picture can be taken. In continuous/servo AF mode, focusing doesn’t stay locked, and instead the camera will keep adjusting focus to hold the subject sharp for as long as you want it to. This is better formoving subjects, like action or wildlife. Choosing an AF Area The AF mode governs the options you have when selecting the AF area; that being the part of the frame used to focus. In single/one-shot AF, you can choose to employ a single AF point, and this can be moved around the frame, for instance to sit close to the subject’s eyes. This is the most accurate way of autofocusing, but the number of AF points (and therefore how easily you can align them with what you’re shooting) depends on your camera. You can also use an expanded AF area to make it more

Words & pics by Kingsley Singleton

Where you focus is one of the most important decisions in a photo, working with your compositional decisions to create the heart of the image. Get it wrong, even by a little and you can wreck an otherwise excellent shot. And unlike changes to framing or exposure it’s impossible to bring blurred areas back into focus (on a regular camera at least). What is Autofocus? Many modern cameras can focus in a completely automatic way, detecting the type of subject you’re shooting, whether it’s moving or not, and even gauging whether the subject is smiling or not to trigger the shutter. But although these highly automated options are fine for some shots, ideally, the decisions should be yours. So, to open up the full range of options, first make sure you’re not shooting with the main mode dial set toAuto. Switch to aperture- or shutter priority, program or manual and you’re free to explore. Autofocus (AF) as most photographers know it isn’t completelyautomatic soyoucanbend it your will. It works by giving you two main choices to make; the AF mode and the AF area. The AF mode should be picked first anddepends on what type of subject you’re shooting; for example if it’s moving or static, andhowmuch time youhave towork.

Above The main focus switch sets either manual or autofocus, from there you choose the mode and area.

Single/one-shot AF mode and single-point AF area In single/one-shot AF mode, the camera’s autofocus system will find the focus and lock it, so that if the subject moves, focusing will need to be repeated. For accurate results, this mode is used with single AF area, using either the point in the centre of the frame, or one close to the area where the focus should fall. Therefore it’s best for stationary or slow-moving subjects.

automatic and use several or all of the AF points to focus at the same time. In continuous AF mode, you can also use a single AF point, or an expanded array and this is great for tracking moving subjects. Many cameras also have a ‘3D’ mode, that tracks the subject around the frame. What about live viewAF? Although still using single and continuous settings, AF in live view works differently. For one thing, because it doesn’t rely on individual AF sensors, you can focus on any part of the frame. There are also special modes like face detection that lock on to portrait subjects by recognising the basic shape of a human face which is useful if you’re working fast or composingwith the camera held very high or low. Next month: Expert focusing tips.

Continuous/servo AF mode and Auto AF area In this configuration, which is better for moving subjects, the AF mode is set to continuous/servo, and will keep focusing and refocusing on the subject in case it moves. Single-point AF area can still be used but for moving subjects it can be better to use an Auto area, which uses a group of AF points (either a selection of the total or all of them) to focus.

Software skills Sharpening in Photoshop

When sharpening in software, it’s important to remember that you’re not actually bringing a blurred picture back into focus, and can’t add detail that’s not already there. All you can do is make what you have recorded appear sharper. That said, a little sharpening can make a huge difference to pictures, whether they’re fractionally out of focus or pin-sharp at the point of capture. Digital sharpening is achieved by increasing contrast in the image, but this increase is restricted to the edges, so it’s not the same as simply turning up the global contrast. What is an edge and howmuch contrast is applied is governed by the settings you use. In Photoshop and Elements, Unsharp Mask (Filter>Sharpen>Unsharp Mask or Enhance>Unsharp Mask) is a good example of how sharpening works. There are three settings; Amount controls howmuch contrast is added to edges; Radius sets the width of the effect either side of an edge, so lower settings look more natural; and Threshold governs what is a considered an edge, with a setting of 0 seeing that everything

is sharpened, and higher settings less, so it allows you to restrict the effect a little. The amount you should apply depends on a lot of things, not least your own taste. Generally, unless you’re after a very rough effect, settings shouldn’t be pushed too high. Nextmonth: Selective sharpening.

1. Unsharpened This is the original image without sharpening. The subject is in focus, but we can still improve the look of the details by adding sharpening using the Unsharp Mask filter in Photoshop or Elements (Filter>Sharpen>Unsharp Mask or Enhance>Unsharp Mask).

2. Sharpened Using settings of 100% for amount 1.0px for Radius and 2 levels for Threshold, a good level of detail is returned and the grass and the horse’s hair looks more textured, without overdoing it.

3. Over-sharpened Here, with a setting of 150% for

Amount, the effect is too extreme. The picture looks rough, rather than crisply detailed and unnatural fringing is appearing due to the too-high Radius of 3.0 pixels that’s been used.

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