ChobialFocus: getting the right thing sharp
Focus decides where the viewer looks. If the eyes are soft and the ear is sharp, the photo feels wrong, however good the light was. This lesson is about getting the sharp part to land where you meant it.
The idea
A lens can only focus at one distance at a time. Things at that distance are sharp. Things nearer or further get gradually softer. The zone that still looks acceptably sharp is called the depth of field.
Depth of field depends on three things:
- How close you are. The closer the subject, the thinner the sharp zone. A flower from a hand's width away can have a background dissolved into colour; a mountain range is sharp from front to back.
- The lens's focal length. Longer lenses (2×, 5×) give a thinner zone than wide ones (0.5×) at the same framing.
- The aperture and sensor size. Big cameras with wide apertures give very shallow focus. An iPhone's small sensors give deep focus, which is why most phone photos are sharp nearly everywhere.
So on an iPhone, the way to a soft background is to get close and put distance behind your subject.
Where to focus
- People and animals: the nearest eye. It's the first thing anyone looks at.
- Close-ups: the part that tells the story, such as the centre of a flower or a water drop, because the sharp zone may be only millimetres deep.
- Landscapes: about a third of the way into the scene, not the far horizon. That keeps the foreground sharp too.
In Chobial
Tap, or follow
- Tap the viewfinder on what should be sharp. An orange frame marks where the camera focused and metered.
- People and pets get thin white corners when the camera finds them. Tap inside the corners and they turn green: focus and exposure now follow that subject as it moves. Tap somewhere else to stop.
Focus by hand
Autofocus struggles through glass, in the dark, with low-contrast subjects and very close up. Take over:
- Open the controls and tap FOCUS.
- Drag the dial between NEAR and ∞ (infinity).
- A loupe magnifies the spot you're focusing on, and focus peaking outlines sharp edges in red. Turn until the red sits on your subject.
- Tap AUTO to give focus back to the camera.
Move the sharp zone
- Line up three objects on a table at different distances: one close to the phone, one in the middle, one at the back.
- Get low and close to the front one. Tap FOCUS, turn on peaking if it isn't already, and turn the dial until the red outlines the front object. Take a photo.
- Turn the dial until the red moves to the middle object, then the back one, taking a photo each time.
- Step back a metre and repeat. Notice how much more is sharp from further away. That's depth of field growing with distance.
Next: composition, or where to put things in the frame.
Questions
How do I get a blurry background on an iPhone?
Get closer to your subject and further from the background. Depth of field shrinks fast as you get close. The 2× or longer lens, from a few steps back, also helps. Chobial doesn't fake the blur with software; what you get is what the lens really does.
Why does autofocus keep jumping around?
It's guessing what matters. Tap what you want, or tap inside the white corners around a person or pet so focus follows them. For a still subject, switch to manual focus and it won't move at all.
What's the closest I can focus?
It depends on the lens. Turn the FOCUS dial to NEAR and move the phone slowly toward your subject until it snaps sharp. That distance is your lens's limit. On many Pro iPhones the 0.5× lens can focus closest of all.