Sharpness

Learning goal

In a landscape where you want everything to be sharp, from a rock half a meter away to a mountain kilometers away, you will be able to decide in the field whether a single frame can carry this. You will explain the aperture range at which your lens works sharpest, why in landscape the range between f/8 and f/11 is so often chosen, and why stopping down further softens the whole frame beyond a certain point. You will place the focus with the double-the-distance method, which can be applied without calculation, and check both front and back by enlarging on the screen. When a single frame isn't enough, you will move to combining several frames, choosing your method according to grass swaying in the wind and a person standing in the frame. You will check the person's face, especially on dark skin left in shadow or on shining light skin, by enlarging at eyelash and eye level.

The question

Your friend enlarges the lakeside frame on the computer. The lichens are sharp as a pinpoint, but the mountain's ridge behind is soft as cotton. The next day they go to the same place and this time focus on the mountain; now the mountain is sharp, the rock blurred. They stop the aperture down to f/22 and shoot one more frame; both are a little sharper, but the whole frame seems to be behind a thin veil. How do you build a landscape sharp from front to back, and can both the rock and the mountain be sharp at the same time?

Context

In the sharpness section you calculated the nearest focus distance that extends sharpness to infinity, and how this distance changes with focal length and aperture (Lesson 10.9). In close-up stacks you tried combining frames focused at different depths and taking the sharpest area of each (Lesson 22.5). And you remember from the aperture lesson that at very narrow openings light bends at the edge of the hole and softens the photo (Lesson 8.2).

Landscape is where these three pieces of knowledge make you decide together. When you build a near-far frame, the distance between the rock and the mountain can be bigger than a single slice of sharpness can carry. Then you either choose the focus and aperture so that the slice covers both, or, instead of forcing this in a single frame, you shoot several frames and combine them. Knowing which is possible in the field, without looking at a calculator, is the subject of this lesson.

Simple explanation

Which aperture is sharpest?

A sweet spot is the aperture range at which a lens gives detail most cleanly. Many lenses work a little soft at the edges at their widest aperture; stopping down two or three stops reduces the lens's flaws and the image sharpens. Stopping down further, on the other hand, brings diffraction into play and the whole frame slowly softens. The place where these two effects balance is, for most lenses on full-frame cameras, roughly somewhere between f/5.6 and f/11. The exact range changes from lens to lens; shooting the same scene with your own lens at different apertures and comparing by enlarging gives a more reliable answer than a table.

This is also why the range between f/8 and f/11 is chosen so often in landscape: it is close to the narrow end of the sharpest range and deepens the slice of sharpness as much as possible. f/16 and f/22 give a deeper slice, but take back the sharpness they gain from the whole frame through diffraction. As the sensor gets smaller, the aperture at which diffraction becomes visible also widens; on a small-sensor camera even f/8 can start to soften the frame slightly.

Where do you put the focus?

The double-the-distance method is multiplying by two the distance of the nearest thing you want sharp in the frame and putting the focus at that distance. If the rock is half a meter away, you put the focus at one meter. This method uses the hyperfocal calculation in reverse: when you focus at the hyperfocal distance, sharpness starts at about half of it and stretches to infinity. If, at the aperture and focal length you chose, the hyperfocal distance is shorter than this doubled distance, both the nearest thing and the distant mountain stay inside the slice; if it is longer, the mountain falls outside the slice.

On a full-frame camera with a 16 millimeter lens at f/11, focusing at one meter, sharpness stretches roughly from forty-five centimeters to infinity; both the rock and the mountain stay in a single frame. If you use the same aperture with 24 millimeters, focusing at one meter ends sharpness at around two meters and the mountain softens; to bring the mountain in you need to move the focus to one meter seventy-five centimeters, and this time sharpness starts only about ninety centimeters in front, leaving the rock at half a meter outside the slice. In other words, how close you move in on the rock and how wide a lens you use decide whether a single frame will be enough.

What do you do if a single frame isn't enough?

If the rock is close and the lens isn't wide enough, you shoot several frames instead of one: one focused on the rock, one on the lake between, one on the mountain. A tripod keeps the framing fixed; the frames are combined afterward and the sharp area of each is taken. In landscape two or three frames are often enough. If wind is swaying grass or leaves, shapes shift between frames and ghost traces appear in the combination; waiting for a calm moment, or taking the moving area from a single frame, reduces this problem.

A sharpness check is enlarging the frame you shot on the screen while still in the field and checking the front, middle and back separately. In the rear screen's small image everything looks sharp; softness only shows when you enlarge. If there is a person in the frame, enlarge on their eyes and eyelashes. On dark skin left in shadow, or on light skin shining in the sun, fine details already have little contrast and softness is lost there first. If you are combining, since the person will move between frames, taking their face from a single frame is safer.

Visual evidence

At home your friend shoots the same rock and mountain scene at five apertures and enlarges them side by side. At f/4 the corners of the frame are soft, at f/8 the corners have pulled together, at f/11 almost the same, at f/16 everything has faded a little, at f/22 the frame is behind a veil. They see that for their own lens the sharpest range is between f/8 and f/11.

They return to the shore. The rock is half a meter away, their lens 24 millimeters. When they focus on the rock and enlarge, the lichens are sharp, the mountain soft; focusing on the mountain, the reverse. The rock and the mountain don't stay in a single frame. They fix the tripod and shoot three frames: on the rock, the middle of the lake, the mountain. Wind is swaying the reeds on the shore; they wait for a moment when the reeds stand still.

Your friend's hiking companion standing on the shore, a dark-skinned woman left in shadow, tries not to move through the three frames, but her head turns slightly. In the combined frame both the rock and the mountain are sharp; your friend takes the woman's face from the single frame focused on her eyes, and her eyelashes and the details of her skin can be made out.

Common mistakes

Summary

A landscape sharp from front to back is built by staying in the lens's sweet spot and putting the focus at twice the distance of the nearest thing that must be sharp, or, when this isn't enough, by combining several frames focused at different depths; stopping down to f/22 softens the whole frame through diffraction. The result is checked by enlarging in the field; the face of the person in the frame is taken from a single frame focused on their eyes, and the fine details of dark or light skin are checked separately.

Mini assignment

In this assignment you will find your own lens's sharpness and its limit.

1. From a tripod, shoot a detailed scene at every stop from the widest aperture to f/22 and compare the frames by enlarging them; note your sharpest range.
2. Build a framing with a close element and a distant landscape, measure the close element's distance in steps, put the focus at twice this distance and shoot at an aperture in the sharpest range.
3. Enlarge the frame and check the front and back; if one is soft, shoot two or three frames from the same framing focused at different depths and combine them.

Check yourself

• At which aperture is your lens sharpest, and after which does it start to soften?
• Was the double-the-distance method enough for a single frame in this framing?
• If there is a person in the frame, are their eyes and eyelashes sharp?

Glossary

Mini quiz

1. Why can stopping the aperture down to f/22 soften the whole frame?

• A) Because colors fade as the light drops
• B) Diffraction bends light at the edge of the hole
• C) The focus shifts by itself
• D) The sensor heats up

2. If the rock is a meter and a half away, where is the focus put with the double-the-distance method?

• A) Right on the rock
• B) At infinity
• C) On the mountain
• D) At three meters

3. If a single frame can't keep the rock and the mountain sharp together, what can be done?

• A) Shooting several frames focused at different depths and combining them
• B) Opening the aperture to its widest
• C) Trusting the small image on the rear screen
• D) Putting the focus at a random point

4. If there is a person in the frame, where is the sharpness check done?

• A) On the sky
• B) On the frame's corners
• C) On their eyes and eyelashes
• D) On their shoes

Answers

1. B — At a very narrow opening light bends at the edge, and the sharpness gained is taken back from the whole frame.
2. D — Since the nearest sharp point is a meter and a half away, the focus is put at twice that, three meters.
3. A — Each frame keeps one depth sharp, and in the combination the sharp area of each is taken.
4. C — Softness shows first in the fine details of the face, especially the eyes and eyelashes.

Summary card

• Find your own lens's sweet spot by shooting; in landscape often f/8–f/11.
• f/22 gives depth but softens the frame through diffraction.
• Put the focus at twice the nearest sharp point.
• If that isn't enough, shoot two or three frames from a tripod and combine them.
• Check by enlarging in the field; take the person's face from a single frame, look at their eyes.

Bridge to the next lesson

In the combined frame the rock and the mountain are sharp, but your friend gets stuck on something else: the sky is almost pure white, the color of the pink clouds lost; and when they lower the exposure to save the sky, the rock and the lake sink into darkness. How do you balance a bright sky? The next lesson takes up filters mounted in front of the lens: the polarizer that cuts reflections and darkens the sky, the ND filter that reduces light, and the graduated ND filter that darkens only the upper half of the frame.