Photography News Issue 28 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 to know. This month, how to improve your focusing on moving subjects and how to sharpen selectively in Photoshop or Elements
1. Expand the area While it’s tempting to use the camera’s fully auto AF area for moving subjects – the mode in which all AF points are used and the camera basically decides where the picture shouldbe sharpest – this isnot always the most accurate route. Generally, auto AF area looks for the most contrasty parts of the scene, so it may pick up points of the subject youdidn’twant it to, or choose something else entirely. Being selective is better, and limiting the area used to focus is a good idea, but you don’t need to go all the way back to a single AF point, which is tricky to hold on a moving subject – this is where expanded area AF helps. Expanded area AF is given different names by manufacturers (for instance Nikon’s is called Dynamic AF while Canon’s is called AF Area Expansion), but all systems work prettymuch the same. Essentially, you still pick a single point, but around this, extra AF targets are used (you can decide how many) and this works wherever the point is positioned in the frame. Now, when focusing, if the camera can’t lock on with the chosen point, it will use the others around it as backup. Priority is usually given to the chosen point, but it’s still a good safety net. 2. Use tracking AF Many modern cameras feature automatic AF tracking, which helps follow the target around the frame. Again, this goes by different names from one manufacturer to another, but essentially the systemuses colour
information as well as contrast as its guide. So if the same readings disappear from one AF point and are then detected on another, the camera knows that’s where the subject has moved to. Accuracy, of course, depends on the number of AF points that your camera has, and it works better if you’re following a subject that contrasts with the background, both in colour and shade. 3. Prefocusing On the fastest subjects, especially those moving towards you, even sophisticated, predictive AF tracking systems can struggle. In those cases it’s best to use prefocusing. This requires focusing on a part of the scene that you know the subject will move past or through; for instance a point of a race track where a vehicle will turn, or a rock that you knowand animal will move to. This is different from most other action-focusing techniques, because it’s best done in Single or One Shot AFmode, and you can use a single AF point, too. Focus where required, then shoot as the subject comes into range; you can either time it yourself, or use continuous Drive mode to rattle off several shots, making sure you don’t miss the action. 4. Increase the depth-of-field Here’s something that’s not a focusing technique in itself, but is still very useful in capturing moving subjects clearly; increase the depth-of-field to keep more of the scene in focus. A small change; say from f/2.8 to f/4 or f/5.6 is often enough to reduce errors, and when shooting with telephoto
Words & pics by Kingsley Singleton
Focusing on static subjects is fairly straightforward, and once you’ve locked on (in Single or One-shot AF mode), so long as you or they don’t move, there shouldn’t be any problem. It’s moving subjects, that present more issues. Not only will their distance from the camera be changing all the time, they may move erratically, with their position changing in the frame. Using your camera’s Continuous or Servo AF mode will keep hunting for them, it’s still possible to get more misses than hits, unless you tailor other settings in the right way as the focus may slip to unwanted areas.
AFAreas if your subject is fast moving and tricky to follow, use an expanded array of points, as above. Or, if you’re patient, you can prefocus on parts of the scene the subject will move through, below.
lenses, you’ll still achieve a pleasing blur in the background. As a bonus, you’ll find that stopping down from the maximum apertures improves optical quality, too. 5. Use focus limiting Many telephoto (and macro) lenses have a focus limiter switch and using this can seriously speed up the process of locking on when time is
short – as it usually is with moving subjects. The focus limiter allows you to trim the area over which the lens looks for focus, so while a model like Nikon’s 200-500mm f/5.6 might normally focus from 2.2m to ∞ , if you know the subject isn’t coming that close you can reduce the area (to 6m to ∞ ) stop it hunting for the subjects or accidentally locking on to foreground objects, such as undergrowth.
Above If focusing is taking too long, try using the focus limiter switch, which restricts the focusing range.
Nextmonth Manual focusing tips
Just like focusing, sharpening should be aimed at just the part of the pic that you want to be the focal point. In a portrait, this might be the face alone, or the eyes. In a landscape you might want to sharpen only the foreground elements and avoid the sky. Certain parts may also need more sharpening than others, so you might sharpen a rock texture more than water in a stream. All this means you need to learn how to sharpen selectively. In Photoshop that involves selecting the area to sharpen first. For broad areas, the Marquee tools are best, but for detailed parts it’s the Lasso tools which allow greater control. Nextmonth: Selective sharpening in Lightroomand Photoshop’s Camera Raw. Photoshop skills Selective Sharpening
1. Select the area to sharpen Pick the appropriate Selection tool – here, as we’re working on the eyes of a portrait, it’s the Lasso tool (press L or Shift+L). Now, in the Options bar, set Feather to 0 and draw around the parts of the image you want to sharpen. You can draw around both eyes together, or make individual selections by completing the first, then adding to it by holding Shift and drawing again. If you need to remove some of the Selection hold Alt and cut into it.
2. Refine the Selection Click Refine Edge in the Options bar and set the Feather amount – this is the softness of the transition between selected and unselected areas; 0px gives a hard edge, which doesn’t look photographic, so use the preview to gauge how much softening looks good. The amount required depends on the pixel dimensions of the image and you can cycle through the previews with F, highlighting the selected and unselected areas. Hit OK when done.
3. Apply the sharpening Now the Feather has been added, you can add the sharpening. Go to Filter>Sharpen>Unsharp Mask and use the 100% preview to estimate the level of sharpening required. The level of sharpening required also depends on the pixel dimensions of the image (and how soft the original is). Here an Amount of 125%, a Radius of 1px and a Threshold of 2 Levels adds a crisp look without over-sharpening. Hit OK and then save the sharpened version as new file so you don’t lose the original.
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