Cleaning the lens

Learning goal

You will be able to recognize the most common reason a photo you take with your phone comes out hazy, milky, or with halos around the lights. You will know why a phone's camera glass gets dirty so easily, what traces the dirt leaves in the photo and how to diagnose a smudge at a glance; and you will learn to clean the glass safely, to check how the case and the screen protector affect the camera, and to build a cleaning habit of a few seconds before an important frame.

The question

One evening, walking down the street with your friends, you see a beautiful scene: the reflections of the streetlights on the wet pavement, the warm light of a shop window. You take out your phone and shoot. When you open the photo, there is a milky white, blurry halo around every lamp; the light of the shop window has spread like a cloud of fog, and the whole sharpness of the scene is gone. Your phone is new, the settings are right, and there is enough light.

Why do phone photos sometimes come out hazy? The answer to this question is usually not in the camera but in your pocket. All day long, your phone's camera glass touches your fingers, your pocket, your bag and your face. The thin layer of grease that builds up on it is hard to see with the eye, but it is enough to scatter light. A fingerprint smudge is the most common and most sneaky killer of quality in phone photography.

Context

Someone who carries a camera puts a cap on the lens, protects it in a bag and hardly ever runs a finger over its front glass. A phone's cameras, on the other hand, are bare. You pick up your phone dozens of times a day, and your fingers often rest on the back of the phone, right next to the camera. The dust in your pocket, the crumbs in your bag, the cream on your hands and the oil on your face all travel to that small piece of glass. The front camera doesn't escape either: thumbs touching the screen and cheeks pressed against the phone leave traces on the glass of the selfie camera.

You saw the general cleaning order for a camera lens in the previous module. In this lesson we focus on the problem specific to the phone: why dirt builds up so often and so silently, how it looks in the photo, and a small habit that prevents it. The good news is that this is the easiest problem in photography to fix. It needs no setting, no knowledge, no new equipment; only a few seconds and a clean cloth.

Simple explanation

Why does dirt create haze in a photo?

Clean glass lets light through smoothly and gathers a sharp image on the sensor. Grease on the glass, however, behaves like thousands of small, irregular lenses. It turns part of the light away from its true path and spreads it to other places in the image. The result is a thin veil of milk drawn over the whole photo: blacks turn gray, colors fade, sharp edges soften. This scattering of light inside the lens or on the glass, which lowers contrast, is called flare.

This effect becomes most noticeable around strong light sources. A streetlight, a window, the sun or a candle throws a halo around itself when it passes through smudged glass. Because the grease layer is smeared by the movement of a finger, these halos sometimes stretch out in streaks in one direction, and the lamps look like stars or comets. In the daytime, in plenty of soft light, the same smudge can stay too faint to notice; that is why dirt often shows up only in a frame shot at night or against the light.

How do you diagnose a smudge?

When a photo comes out hazy, there is a simple test to find the cause: turn the phone over and look at the camera glass from a side angle, in front of a light source. Clean glass looks steady and deep. On smudged glass, you can make out the swirls of a fingerprint, a greasy shine or small specks of dust. If you aren't sure, take a photo of a single lamp in a dark room. If the lamp sits on the screen like a sharp point, the glass is clean; if there is a halo or streaks around it, the glass is dirty.

Dirt isn't the only cause, but it is the most frequent one. A crack or a scratch on the camera cover glass in front of the camera, or a screen protector or case spilling over the edge of the glass, can leave similar traces. If the edge of the case sticks out a little in front of the camera, one corner of the photo darkens, or the flash light bounces inside the case and mixes into the image. A thick or poor-quality camera protector can also scatter light. If the haze continues even after you have cleaned the smudge, these are the next things to look at.

How do you clean the glass safely?

The best tool for cleaning a phone's glass is a soft microfiber cloth made for cleaning glasses or screens. First, gently blow the dust off the glass; if a grain of sand or hard dust gets rubbed along with the cloth, it can scratch the glass. Then move the cloth over the glass in small circles, without pressing. A paper tissue, the end of a T-shirt or a jacket lining may seem to work at first glance, but they leave fibers and spread the grease instead of cleaning it. Stay away from harsh chemicals, harsh alcohol-based cleaners and abrasive materials too; they can damage the thin coatings on the glass.

The real solution, though, is a habit. Wiping the camera in a few seconds before an important photo is one of the most rewarding small moves in phone photography. Many photographers carry a microfiber cloth in their wallet or inside their phone case. Even if you don't have a cloth with you, wiping gently with a clean, dry cotton fabric is better than not wiping at all.

This small habit matters even more when you photograph people. One of the things that shows the shape of a face is the small, bright points of reflection that appear on the forehead, on the bridge of the nose and on the cheekbone. On darker skin, these points are the main signs that draw the lines of the face. Smudged glass scatters these sharp points and turns them into a blurry glow spread over the face, and the face loses its shape. On lighter skin, the same smudge can blend the bright areas together and turn the face into a pale blur. Clean glass shows everyone's face in its own light.

Visual evidence

Picture two portraits of a friend, on the same evening, on the same street. Behind them are rows of streetlights and the bright window of a café. Your friend has dark skin, and the warm light of the window falls on their face. The phone's camera is used just as it came out of the pocket, without being wiped.

In this first frame, every streetlight is like a big, milky white ball. Thin, diagonal streaks stretch sideways from the lamps; they trace the direction of the fingerprint. The light of the window has spilled over your friend's shoulder and hair, and a foggy transition has formed between the background and the face. On the face, the bright points on the nose and forehead have spread out and disappeared; the face looks flat and grayish.

You wipe the camera for a few seconds and take the same frame again. The lamps are now small, sharp points of light. The edges of the window are sharp, and the products behind the glass can be made out. On your friend's face, the small glints on the forehead and cheekbone stay in place and draw the lines of the face; the skin is warm and deep. The same phone, the same settings, the same light. The difference between them is a few seconds' touch of a cloth.

Common mistakes

Summary

The most common reason phone photos come out hazy is the invisible grease and fingerprints that build up on the camera glass; this layer scatters light, draws a veil of milk over the whole photo and leaves halos around the lights. Checking the glass against the light, wiping it for a few seconds with a soft cloth before an important frame and glancing at the edge of the case are the easiest and most effective quality fixes.

Mini assignment

In this assignment you see the effect of dirt with your own eyes.

1. In the evening or in a dark room, choose a single lamp or a streetlight and take a frame without wiping your camera at all.
2. Turn the phone over, look at the camera glass from a side angle against the light, and note the traces you see.
3. Clean the glass, first by blowing and then with a microfiber or clean cotton cloth in small circles, and take the same frame again.
4. Zoom in on the two frames and compare them; repeat one frame with your front camera too, shooting before and after wiping.

Check yourself

• Were you able to recognize the smudge in the photo from the halo or streaks around the lamp?
• Were you able to see the traces by checking the glass against the light?
• Were you able to describe in words the difference between the frames before and after wiping?

Glossary

Mini quiz

1. What is the most common cause of haze in phone photos?

• A) Grease and fingerprints on the camera glass
• B) The phone's software being old
• C) The phone's battery being low
• D) The screen brightness being low

2. In which situation is smudged glass most noticeable?

• A) When photographing a plain wall on a cloudy noon
• B) When photographing a page of a book in daylight
• C) In frames with strong light sources, such as streetlights at night
• D) In a completely dark room with no light at all

3. What is the right way to clean a phone's camera glass?

• A) Wiping it quickly with the end of a T-shirt
• B) Wiping it with a paper tissue, pressing down
• C) Scrubbing it with a harsh cleaner
• D) First blowing off the dust, then wiping in small circles with a soft microfiber cloth

4. How can smudged glass affect a darker-skinned face?

• A) It increases the detail in the face and makes the pores stand out
• B) It can scatter the small bright points that draw the lines of the face and make it look flat and grayish
• C) It has no effect
• D) It makes the face completely black

Answers

1. A — The thin layer of grease on the glass turns light aside and draws a veil of milk over the whole frame; the problem is usually not in the camera but on the surface of the glass.
2. C — Strong light sources throw halos and streaks around themselves as they pass through smudged glass; in soft daylight the same smudge can stay very faint.
3. D — If the dust isn't blown off first, it can be rubbed along with the cloth and scratch the glass; a soft microfiber cloth and a light circular movement clean without spreading the grease.
4. B — On darker skin, the small bright points of reflection that show the shape of the face spread out into a blurry glow through smudged glass, and the face loses its shape.

Summary card

• The number one cause of haze: invisible grease and fingerprints on the camera glass.
• The sign: halos around lights, streaks, a milky and faded image.
• Diagnosis: examine the glass from a side angle against the light, or shoot a single lamp.
• Cleaning: blow first, then small circles with a microfiber cloth; no T-shirt, no tissue.
• Don't forget the front camera, the edge of the case and the protector.

Bridge to the next lesson

The glass is clean, and light is coming in sharp. Now it's time to decide where to focus that light and how bright to record it. A single touch of a finger on your phone's screen can change both of these decisions at once. The next lesson asks: why does touching the screen change everything? There you will learn to choose the focus by tapping, to set the brightness by sliding your finger, and to lock both by pressing and holding.