Autofocus isn’t always the reliable ally you might expect it to be. Here are 10 shooting situations when it’s a right pain.
1. When there’s not enough contrast
You may have noticed that when you try to focus on fine textures and/or plain surfaces, your camera’s autofocus has a really hard time focusing. Digital cameras have one of two autofocus systems – active (which uses an infra-red focus beam) and passive (which looks for areas of light/contrast). Active autofocus will do a better job of focusing on this type of low-contrast surface, but success isn’t guaranteed.
2. When you’ll frighten the birds
When out in the wilderness, telephoto lenses are essential to get close to timid wildlife. The main problem with using autofocus to shoot animals and birds is that most creatures have excellent hearing. Even the slightest whir from your lens will send them scarpering for cover. Using manual focus is unlikely to create any noise that will disturb the animals you’re photographing.
3. When there’s not enough light
When working in low light, if your lens uses passive autofocus it could really struggle to find focus. This is because this system relies on light and contrast. In this situation your AF Assist lamp may resolve the problem. Failing this, manual focus is your best option. Active autofocus cameras will have less of a problem in this situation.
4. When you want hyperfocal distance
When shooting landscapes and you want great depth-fo-field, you’ll generally need to focus one third into the shot to achieve hyperfocal distance (maximum focus from foreground to infinity). Once the camera is focused on the correct spot it’s important to switch off your autofocus. If you don’t, you’ll find your camera will re-focus every time you depress the shutter button.
5. When you want identical images for HDR
High Dynamic Range photography involves taking three shots of the same scene. One at normal exposure, one two stops underexposed and one two stops overexposed. These three images are then blended together based on exposure to show detail in shadows, midtones and highlights. It’s important to have the focus in each shot identical to ensure successful blending. Like landscape photography, finding focus before switching to manual focus is the best way to stop the camera trying to re-focus every shot.
6. When shooting through glass
When shooting through a substance such as glass, branches, a crowd or grass your autofocus may focus on the wrong object, preferring to focus on whatever’s closest to your selected focus points. By manually focusing you’ll ensure that your chosen subject will be in focus and not what’s in front of it.
7. When using the rule of thirds
Cheaper entry-level DSLRs often have fewer focus points, and concentrate them within the central area of the viewfinder frame. When shooting using a tripod, a subject that falls outside of this area will be easier to focus on manually.
8. When you’re panning
When panning to shoot a fast-moving subject, keeping the subject in focus could be difficult with any of your camera’s autofocus zone options. By manually focusing on a point where you know you subject will cross, you can pre-focus and switch to manual mode to ensure a pin-sharp shot.
9. When you’re using differential focus
Portraiture most often focuses attention on the sitter’s eyes, so ensuring the eyes are sharp is extremely important. Shooting with a wide aperture such as f/2.8 creates a very shallow depth-of-field. If your autofocus accidently focuses on an eyebrow or the tip of an eyelash, you could lose your critical focus. Focusing manually avoids this problem.
10. When you’re shooting insects
When shooting fast-moving insects from close range using a macro lens, autofocus is nigh-on impossible. By switching off your autofocus and focusing your lens to its minimum focusing distance instead, you can rock gently backwards and forwards to find focus. Once you have it, all you have to do is wait for an insect to land.
FACT: DID YOU KNOW?
• The first autofocus SLR was the Minolta Maxxum AF
• The first autofocus medium format camera was the Pentax 645N