Glance at the summary firstThe summary from the end of the lesson, as a road map before you start reading.
The cause of blur can be read in the magnified photo: if there is a sharp plane of focus in the frame, the problem is in the focus point, the focus mode or shallow depth of field; if nothing is sharp, you look for the cause in the direction of the motion trail, in a hazy halo, or in focus that never settled. Not enough light is the common root that gives rise to most of these causes, and on faces, on every skin, you need to look at the eyes and eyelashes so as not to mistake softening or overexposure that erases texture for a sharpness problem.
Learning goal
You will be able to look at a blurry photo and read from the frame where the softness comes from. You will start the diagnosis by magnifying the photo and looking for a sharp place in the frame; you will tell a frame where sharpness fell in the wrong place apart from a frame where everything slid; from the direction of the motion trail you will tell a shaking hand from a moving subject; you will recognize the trace left by a dirty lens and by hunting focus; you will see that not enough light is the common root behind most of these causes; and you will understand that a face looking soft isn't always blur, by checking, on every skin, not the skin's texture but the eye and the eyelashes.
The question
At home, you look at the photos you took one evening in a tea garden. The frame of the tea server walking with his tray is soft, the frame of two neighbors playing backgammon is soft, and the portrait of an older woman laughing under the lamps is soft too. All three look blurry, but all three aren't blurry for the same reason. In one, sharpness may have gone somewhere else, in one the hand may have moved, in one a fingerprint may have been left on the lens.
Why is my photo blurry? There are 7 reasons you can list: camera shake, subject movement, a wrong focus point, a wrong focus mode, shallow depth of field, a dirty lens and not enough light. But memorizing the list isn't enough to look at a frame and find which one is to blame. In this lesson, instead of listing the causes, we will learn to read the trace each of them leaves in the photo.
Context
In Lesson 3.6 we saw that blur doesn't come from a single source, and separated camera shake from a moving subject. What we have talked about in this module on focus added new causes to the list: sharpness can go to the wrong edge, a wrong focus mode can leave a moving subject behind, a shallow slice of sharpness can keep only part of the face sharp. A dirty lens and little light, on the other hand, can imitate all of these causes.
Each cause has a different solution. A shaking hand needs a faster speed or support for the camera, a wrong focus point needs the point moved, a dirty lens needs a cloth. A wrong diagnosis means a wrong solution: if you make the shutter speed faster while the lens is smudged, the photo still comes out soft and you still don't know the cause. That is why we are learning to look first, then to fix.
Simple explanation
Where does the diagnosis start?
Looking at a blurry frame on a small screen tells you almost nothing. Magnify the photo on the screen and slowly go around the frame; this is where blur diagnosis begins. The first question to ask is this: is there a sharp place in the frame? This single question splits the causes into two big groups. If somewhere in the frame, on a fence, the rim of a glass or a sign in the background, you find a sharp line, the camera found sharpness somewhere and the problem is in the choice of that place. If there is no sharp line anywhere, the problem is either in the camera moving, in something in front of the lens, or in focus never settling at all.
We can call this sharp area the plane of focus: the distance where sharpness falls in the frame shows everything at that distance sharp, even if it is in front of or behind the subject. The rest of the diagnosis goes on by looking at the position, direction and width of this plane. If there is no plane, this time you look at the shape of the softness: does it stretch into lines in one direction, or does it spread equally in every direction like a mist?
What does a sharp place tell you?
If the plane of focus is in front of or behind the subject, the camera has focused on the wrong point. If the face is soft but the mortar joints of the brick wall behind are sharp, sharpness has slipped behind the face; if the fence in front is sharp, in front of it. This can be called missed focus, and its solution is choosing the focus area and moving the point onto the eye. The same trace can point to another cause in a moving subject: if you stayed in single-shot focus while the subject came toward you, sharpness stays locked at the distance where the subject was first found, and the plane sits behind the subject, where it passed a moment ago. This is the trace left by a wrong focus mode.
If the plane is on the subject but very thin, the cause is shallow depth of field. If the eyes are sharp while the tip of the nose and the ears are soft, or the near eye is sharp and the far eye soft, the camera has focused in the right place, but the wide aperture has narrowed the slice of sharpness. This may not be a mistake; often it is a conscious choice. But if the front row of a group is sharp and the back row soft, and you wanted everyone sharp, the solution is stopping the aperture down.
What does it tell you if nothing is sharp?
If, when you magnify the frame, everything has stretched in the same direction, an edge appears twice, or point lights have turned into small lines and commas, the camera moved during the shot. This motion blur trail is the signature of camera shake: it usually runs through the whole frame in the same direction and with a similar length. With subject movement, on the other hand, the trail falls only on what is moving; while the legs of a walking person flow, the table and chairs behind stay sharp. This distinction is the frame-reading version of the distinction you learned in Lesson 3.6.
If the softness spreads not in one direction but equally in every direction, and the frame looks hazy and washed out, look at the front of the lens. A lens smudge, that is a fingerprint, grease or fog on the front glass, doesn't erase sharp edges but covers them with a mist; soft rings and halos appear especially around lamps and bright windows. If the frame is equally soft everywhere but not hazy, focus may never have settled: the shot happened while the lens was searching for sharpness, before finding it.
What do you think when light is low and a face is soft?
Not enough light doesn't leave a trace of its own; it gives rise to other causes. As light drops, the camera lengthens the shutter speed, and shake and subject movement grow. The focus system can't find edges to measure and falters. The camera raises ISO and then, to reduce grain, softens the image; this softening can erase fine textures, hair and fabrics, and make surfaces look smooth as wax. If you find one of these traces in a dim frame, the real solution is often adding light to the scene.
This last trace misleads the diagnosis on faces. In dim light, a dark-skinned face can lose its texture to the softening of noise reduction and be mistaken for blur; in bright sun, a light-skinned face can look textureless too when it is overexposed and turns into patches close to white. In both cases the problem isn't sharpness but light and exposure. Check a face's sharpness not from the skin's texture but from the eye, the eyelashes and the line of the eyebrow: if these details are sharp, sharpness is in place, and the place you need to look at is the light.
Visual evidence
You go back to the tea garden frames and magnify them. In the frame of the tea server with his tray, the rims of the glasses and his legs have stretched in the direction he is walking, but the legs of the table behind and the wicker of a chair are sharp. This is subject movement; a shutter speed close to half a second has made the walking man flow. In the frame of the neighbors playing backgammon, the board's pieces and the dice are very sharp, but the faces of the two men are soft: sharpness has slipped to the board in front.
In the older woman's portrait, though, nothing is sharp, and there is a milky white halo around each of the bulbs behind. You look at the front of the lens, and your thumbprint is sitting on the front glass. When you wipe the lens and shoot again, the halos disappear. Finally, you remember the portrait of the dark-skinned tea server you took at dusk; his cheek looks smooth as wax, and at first glance you think it is blurry. When you magnify it, his eyelashes and the single hairs of his mustache are sharp. Sharpness was in place; what erased the texture was the ISO rising in little light, and the softening that came after it.
Common mistakes
Common mistakeApplying the same solution to every blur, for example making the shutter speed faster every time.
If the cause is a dirty lens or a wrong focus point, speed changes nothing. The fix: first magnify, and look at whether there is a sharp place in the frame.
Common mistakeChecking the photo only on the small screen.
On the small screen, sharpness falling in the wrong place and slight shake aren't visible. The fix: for important frames, magnify right after the shot and look at the eyes.
Common mistakeMistaking skin that looks soft for blur.
In little light, softening or overexposure can erase texture. The fix: check sharpness from the eyes and eyelashes; if they are sharp, look at the light and exposure.
Summary
The cause of blur can be read in the magnified photo: if there is a sharp plane of focus in the frame, the problem is in the focus point, the focus mode or shallow depth of field; if nothing is sharp, you look for the cause in the direction of the motion trail, in a hazy halo, or in focus that never settled. Not enough light is the common root that gives rise to most of these causes, and on faces, on every skin, you need to look at the eyes and eyelashes so as not to mistake softening or overexposure that erases texture for a sharpness problem.
Mini assignment
In this assignment you will create blurry frames on purpose and diagnose them.
- Shoot the same scene with a slow shutter speed handheld, then at the same speed leaning on something; magnify and compare whether the motion trail falls on the whole frame or only on what is moving.
- Photograph a face with sharpness deliberately put on the wall behind, and find the plane of focus.
- Leave a very light fingerprint on the edge of the lens and shoot a scene with a lamp in it, then clean the lens and shoot again.
- In a low-light evening hour, shoot a portrait at high ISO; magnify and judge the skin's texture and the sharpness of the eyelashes separately.
Check yourself
- In every frame you magnified, could you say at first glance whether there was a sharp place?
- Could you tell the halo in the fingerprinted frame apart from the lines left by shake?
- On the face in the dim room, did you see that the eyelashes were sharp despite the softness of the skin?
Glossary
| Term | Short definition |
|---|---|
| Blur diagnosis | The work of finding the cause of a soft photo by looking at the traces it leaves in the frame. |
| Plane of focus | The distance where sharpness falls in the frame; everything at that distance looks sharp. |
| Motion blur trail | Edges stretching in one direction because the camera or the subject moved. |
| Missed focus | Sharpness falling in front of or behind the subject. |
| Lens smudge | A fingerprint, grease or fog on the lens's front glass; it covers the image with haze and halos. |
Mini quiz
1. In a portrait, if the face is soft and the brick wall behind is sharp, what is the most likely cause?
- A) Camera shake
- B) A dirty lens
- C) Sharpness slipping behind the face
- D) High ISO
2. If nothing in the frame is sharp and point lights have turned into small lines stretching in the same direction, what is the cause?
- A) The camera moving during the shot
- B) Shallow depth of field
- C) A lens smudge
- D) Wrong white balance
3. If the frame is equally soft in every direction and there are milky white halos around the lamps, what do you look at first?
- A) The focus mode
- B) The shutter speed
- C) The aperture
- D) The lens's front glass
4. On a dark-skinned face shot in dim light, if the skin is smooth as wax but the eyelashes are sharp, what can be said?
- A) Focus was missed; focus again
- B) Sharpness is in place; the ISO rising in little light and the softening erased the texture
- C) The lens is dirty
- D) The hand shook
Answers
- C — There is a sharp plane of focus, but behind the subject; the camera found sharpness and put it in the wrong place.
- A — If lines in the same direction run through the whole frame, the camera moved; subject movement falls only on what is moving.
- D — Haze spreading equally in every direction and halos around lights are the trace of a smudge or fog on the front glass.
- B — If the eyelashes are sharp, sharpness is in place; what made the skin lose its texture isn't sharpness but light and softening.
Summary card
- Magnify first, then ask: is there a sharp place in the frame?
- If the sharp plane is in front of or behind the subject: focus point or focus mode.
- If the plane is on the subject but very thin: shallow depth of field.
- Lines in the same direction: shake; only the moving thing flows: subject movement; haze and halos: a lens smudge.
- Little light gives rise to shake, subject movement and hunting focus; on every skin, check sharpness from the eyes and eyelashes.
Bridge to the next lesson
You have learned to read camera shake from the frame: those short lines running through the whole frame in the same direction. But how fast should the shutter speed be to prevent these lines in advance when shooting handheld, and why isn't this speed the same with a long lens and a short lens? The next lesson talks about the safe shutter speed rule tied to focal length, how far image stabilization stretches this limit, and what it can't solve at all.