Balancing windows and interior light

Learning goal

You will be able to find, in stops, the brightness difference between the inside of a room and the outside seen through its window, by taking metering from two separate points. Where this difference is bigger than the camera can carry in a single frame, you will bracket the same frame with different exposures and combine them, or bring the two sides closer by adding light inside with a flash. You will set up an arrangement where the shutter speed decides the window and the flash decides the room; you will choose a natural balance in which what is seen through the window is readable, the room is bright and the window still stays brighter than the inside. You will see how automatic merging spoils a moving person, and take the face by hand from a single frame. You will make sure that a dark or light face in front of the window isn't lost against the light, with a soft flash bounced off the ceiling.

The question

At home your friend opens the studio apartment frame on a large screen. The corners are bolt upright, the woman's smile is in place, even the pattern on the sofa's fabric can be picked out. But the window behind the table is a flat, snow-white rectangle inside its frame; there is no plane tree, no sky, even the curtain's edge has melted into the white. Yet when they were in the room and looked out of the window, the tree's leaves and the roofs of the buildings behind could be seen clearly. The eye had seen both at once, the camera only one. Why does the window come out pure white?

Context

In the bracketing lesson you tried shooting the same scene one after another with several different exposures, and the step between these frames (Lesson 9.8). In the flash and ambient light lesson you learned that the shutter speed decides the ambient light while the flash's power decides the subject the flash lights, and that the two can be set separately (Lesson 19.4). In the bouncing lesson you also saw turning the flash head to the ceiling and bringing the light back down as a broad, soft source (Lesson 19.2).

A room with a window is where these three are used together. When the eye looks at a window it adjusts itself at once to the outside's brightness, and when it turns back to the room, to the inside again; it adds the two images together and thinks it sees both in detail. The camera, on the other hand, has to choose one of the two worlds with a single exposure. In this lesson you will learn two ways of removing that choice: combining several frames, and adding light to the room.

Simple explanation

How much difference is there between inside and outside?

Interior–exterior range is the difference between the brightness of a surface inside a room and the brightness of the outside seen through the window, and it is measured in stops. To find it, you switch the camera to spot metering and take a reading first from a surface in the middle of the room, then from the tree or wall seen through the window; the number of steps between the two shutter speeds gives the difference. On a sunny day this difference easily reaches five stops, and grows even more in a corner far from the window; on a cloudy day or in the late afternoon it shrinks.

The size of the difference explains why you met a snow-white window. When the camera is exposed for the room, the window gets five or more stops too much light and goes past the white point; the detail there isn't recorded at all. When it is exposed for the window, on the other hand, the room sinks into shadow, and trying to open up the dark regions magnifies the noise. If the difference is small, a single RAW frame can carry both sides; as it grows, you need to turn to one of two ways.

How does bracketing rescue the window?

In bracketing you put the camera on a tripod and shoot the same frame with different shutter speeds: one for the room, one for the window, one between the two. The aperture and focus stay fixed; only the time changes. The program then combines these frames and, in each region, takes information from the frame where the detail is best recorded.

Window balance is the brightness relationship, in this combination or in a flash shot, in which what is seen through the window is readable, but the window still stays brighter than the room. When the outside is pulled to the same brightness as the inside, the room looks as if pasted in front of a photo; the outside staying a stop or two brighter is close to what the eye sees when it looks at the window. This isn't a rule but a preference; but a frame where the window looks darker than the inside seems artificial to most viewers.

Automatic merging struggles with everything that moves between frames: leaves swaying in the wind, a curtain or a person fidgeting where they sit can look doubled or half transparent. Manual blending is laying the frames on top of each other as layers and taking each region with a mask from a single frame. The window comes from the darkest frame, the room from the middle frame, and a face from the single frame where the eyes are open; so nothing that moves is split in two.

How does a flash balance the room?

In balancing with a flash the order is reversed: first you choose a shutter speed and aperture for the window, then you light the room with the flash. Because the shutter speed is much longer than the flash's burst, it decides the outside's brightness, while the flash's power decides the room's. Shortening the shutter speed darkens the window but doesn't change the room; raising the flash's power opens up the room but doesn't touch the window. These two dials work independently of each other.

A flash bounced off the ceiling fills the room softly and in a color close to the window light. A warm lamp on the ceiling, on the other hand, stays an orange smudge between these two daylights; turning it off or leaving it knowingly as a warm glow is your decision.

Someone standing in front of the window is against the light: in an exposure set for the window, their face turns into a shadow. On dark skin this means all the detail is lost; on light skin the face shifts to gray and its edges blend into the window's white. A flash bounced off the ceiling lights the face softly from the front and above; a flash fired straight at the face, on the other hand, leaves bright spots on the forehead and cheekbones.

Visual evidence

The next morning your friend goes back to the apartment. With spot metering they read one eighth of a second from the table and one two-hundred-fiftieth from the plane tree seen through the window: an interior–exterior range of five stops. They set up the tripod in yesterday's place and shoot three frames at f/8, at one eighth, one thirtieth and one hundred twenty-fifth of a second.

In the automatic merge the window has opened up: the plane tree's leaves, the roofs behind, a blue sky. But the face of the owner sitting at the table is blurred because she turned slightly between two frames, as if two faces were laid on top of each other. Your friend opens the three frames as layers; they take the window from the shortest frame, the room and the face from the middle one; in that frame the woman stayed still with her eyes open, while in the long one-eighth frame her face has shaken slightly. The face is sharp, the window reads.

Then they try the flash. They set the shutter speed to one hundred twenty-fifth, turn the flash head to the ceiling and with a few tries bring its power to yesterday's brightness of the room. In a single frame the window, about a stop brighter than the inside, the plane tree reads; the room is bright. The dark-brown-skinned woman's face is lit by the soft light coming down from the ceiling; there is no shine on her forehead, the warm brown on her cheeks and the braid of her hair can be picked out.

Common mistakes

Summary

The window comes out pure white because the difference between inside and outside often exceeds five stops, and an exposure set for the room doesn't record the window's detail. Bracketing and combining, or choosing the shutter speed for the window and lighting the room with a flash bounced off the ceiling, balances the two sides; a moving person is blended by hand, while the face in front of the window is kept in its own tone with a soft flash.

Mini assignment

In this assignment you will balance a room with a window in two ways.

1. At a sunny hour, in a room with a window, take spot readings from the middle of the room and from a surface seen through the window; write down the interior–exterior range in stops.
2. From a tripod, with the same aperture, shoot three frames for the room, for the window and between the two; merge one automatically, blend one by hand.
3. If you have a flash, choose the shutter speed for the window, turn the flash to the ceiling and light the room; seat someone in front of the window, get permission, and see whether their face is lost against the light.

Check yourself

• How many stops is the interior–exterior range you measured, and could a single frame carry it?
• Does the window look a little brighter than the room, or the same as the room or darker?
• Is the face in the frame in one piece and in its own tone?

Glossary

Mini quiz

1. How is the interior–exterior range found?

• A) By looking at the middle of the histogram
• B) By taking separate spot readings from the room and the window and counting the shutter speed difference
• C) By enlarging the frame on the screen
• D) By firing the flash

2. In balancing with a flash, what decides the window's brightness?

• A) The flash's power
• B) The flash's color
• C) The shutter speed and aperture
• D) Turning the flash to the ceiling

3. Why does pulling the window to the same brightness as the room often look artificial?

• A) Because the eye is used to seeing the window brighter than the inside
• B) Because the colors are spoiled
• C) Because the frame is noisy
• D) Because the verticals tilt

4. How is the face of a person who fidgets between frames protected in the merge?

• A) By shooting more frames
• B) By turning the frame black and white
• C) By moving the person to the edge of the frame
• D) By taking the face, in manual blending, from the single frame where the eyes are open

Answers

1. B — The number of steps between the two readings gives the stop difference between inside and outside.
2. C — The flash's burst is short; the outside's light is gathered by the time and the opening.
3. A — The outside staying a stop or two brighter is close to what the eye sees when it looks at the window.
4. D — A face coming from a single frame isn't split in two and doesn't look blurred or doubled.

Summary card

• Measure the interior–exterior range: two spot readings, room and window.
• If the difference is large, bracket; if there is movement, blend by hand.
• With a flash: the shutter speed decides the window, the flash power the room.
• Let the window stay a stop or two brighter than the room; this is a preference.
• A soft flash bounced off the ceiling for the face in front of the window.

Bridge to the next lesson

Pleased with the shoot, the owner makes your friend another offer: on the top floor of the office block where she works there is a glass meeting room that sees the whole city. When your friend goes up there, the view is breathtaking, but in the thick glass in front of it the room's lamps, their own reflection and the camera's lights appear. How do you photograph a city from above? The next lesson takes up finding a location that sees the city and avoiding reflections when shooting through glass.