Light and ExposureLight and Exposure

Digital Photography - 2863Digital Photography - 2863

The area of visible light is tiny on the entire electromagnetic energy spectrum.

The area of visible light is tiny on the entire electromagnetic energy spectrum.

The area of visible light is tiny on the entire electromagnetic energy spectrum.

The area of visible light is tiny on the entire electromagnetic energy spectrum.

This narrow spectrum of visible light is what your digital camera’s sensor responds to.

This narrow spectrum of visible light is what your digital camera’s sensor responds to.

This visible spectrum, the light that we see, ranges between about 400 and 700 nanometers in

wavelength.

This visible spectrum, the light that we see, ranges between about 400 and 700 nanometers in

wavelength.

It is possible to take photographs using infrared radiation.

Minor WhiteBarns and Clouds

1955

Minor White used infrared film, but digital photographers can use an

infrared filter.

Road with Poplar Trees, 1955

Infrared filters block all visible light rays and let in only infrared radiation to react with your sensor.

You will need a long exposure time - usually more than a second in daylight even at your widest aperture - to get satisfactory results.

What is “Exposure?”

What is “Exposure?”

Exposure = Intensity x TimeExposure = Intensity x Time

Intensity is the amount of light that reaches the light sensor

Intensity is controlled by the aperture

Time is the length of time the sensor is exposed to the light

Time is controlled by the shutter speed

Intensity is the amount of light that reaches the light sensor

Intensity is controlled by the aperture

Time is the length of time the sensor is exposed to the light

Time is controlled by the shutter speed

In order to get a good exposure, you must be able to ascertain the amount

of light that is hitting your subject.

In order to “read” the amount of light striking your subject, you need some type of exposure

or light meter.

There are external, hand held meters...

There are external, hand held meters...

There are two basic kinds of

exposure meters:

There are two basic kinds of

exposure meters:

and meters built right into your camera

and meters built right into your camera

Some exposure meters read the light that is reflected off your subject.

Other exposure meters, called incident-light meters measure the amount of light falling

on the meter itself.

A hand-held exposure meter can be one that measures either reflected or

incident light.

In your camera, the meter is called a through-the-lens, (TTL) meter and usually measures the overall light level.

When coupled with your camera the meter calculates what aperture and shutter speed will produce an overall light level that equals middle gray.

In more sophisticated cameras, you can set the controls to do more

precise metering.

Of course, how you hold the meter depends on the type of meter you are

using.

Of course, how you hold the meter depends on the type of meter you are

using.

In order to get the best results with your digital

camera, it is advisable to learn to interpret the camera

readings or meter readouts of your particular camera.

In order to get the best results with your digital

camera, it is advisable to learn to interpret the camera

readings or meter readouts of your particular camera.

One of the ways your camera helps you judge whether you are making a good exposure is by

showing you histograms.

One of the ways your camera helps you judge whether you are making a good exposure is by

showing you histograms.

A histogram is a graph that shows the brightness values of all the pixels in an image.

A histogram is a graph that shows the brightness values of all the pixels in an image.

Histograms show a range of 0 to 256.White is at the right at the 255.

Black is at the left at 0.Middle gray is shown in the middle at 128.

Histograms show a range of 0 to 256.White is at the right at the 255.

Black is at the left at 0.Middle gray is shown in the middle at 128.

0 128 255

The graph shows how much of each tone is captured in the photograph.The graph shows how much of each tone is captured in the photograph.

Black Middle Gray White

In this histogram, you can see that most of the tones fall in the middle or medium

range. There are few highlights and few shadows.

In this histogram, you can see that most of the tones fall in the middle or medium

range. There are few highlights and few shadows.

There are several ways to use the meter built in to your

camera.

There are several ways to use the meter built in to your

camera.

Method 1:Using a gray card

Method 1:Using a gray card

Gray cards can be purchased at

any camera store.

Gray cards can be purchased at

any camera store.

To use a gray card, hold the card up to the subject you are about to photograph.

Make sure the card fills the entire viewfinder.

To use a gray card, hold the card up to the subject you are about to photograph.

Make sure the card fills the entire viewfinder.

Remember to capture all of the gray card when getting your meter readings.

Remember to capture all of the gray card when getting your meter readings.

With your camera set to auto or program, let the in-camera meter

suggest a possible exposure.

With your camera set to auto or program, let the in-camera meter

suggest a possible exposure.

Then change your camera mode to manual and choose the settings or their equivalent before taking your

picture.

Then change your camera mode to manual and choose the settings or their equivalent before taking your

picture.

“equivalent?”“equivalent?”

more on that later...more on that later...

Using a gray card works well

under studio conditions.

Using a gray card works well

under studio conditions.

A gray card is 18% gray.A gray card is 18% gray.

If you are ever in a landscape situation without a gray card, you can use grass or green tree leaves to meter. They are very close to the 18% gray value.

If you are ever in a landscape situation without a gray card, you can use grass or green tree leaves to meter. They are very close to the 18% gray value.

Also, in a pinch, you can meter off your hand.Just be sure to use your palm.

The back of your hand is usually darker.(Obviously, this method depends on your skin tone.)

Also, in a pinch, you can meter off your hand.Just be sure to use your palm.

The back of your hand is usually darker.(Obviously, this method depends on your skin tone.)

Method 2:Using Histograms

Method 2:Using Histograms

First, you must set your camera to display the histogram right after you

have taken your picture.

First, you must set your camera to display the histogram right after you

have taken your picture.

Then after taking your first shot, check the histogram to see if you have good

tonal coverage.

Then after taking your first shot, check the histogram to see if you have good

tonal coverage.

Adjust your exposure (either the shutter speed or the aperture)

manually and then retake the picture.

Adjust your exposure (either the shutter speed or the aperture)

manually and then retake the picture.

Reading a histogram takes some practice.

Reading a histogram takes some practice.

But it can ultimately be more informative than the actual photo that

shows on your camera’s monitor.

But it can ultimately be more informative than the actual photo that

shows on your camera’s monitor.

Each of these photographs is correctly exposed for the subject.

Each of these photographs is correctly exposed for the subject.

Simplified Histograms

Method 3:Metering for Specific Situations

Method 3:Metering for Specific Situations

Exposing an Average Scene

Exposing an Average Scene

What is an“average scene?”

What is an“average scene?”

one where all the different tones when averaged together will equal a middle gray.

one where the scene is evenly illuminated as viewed from the camera position.

one where the darks and lights are distributed fairly evenly around the scene.

one where all the different tones when averaged together will equal a middle gray.

one where the scene is evenly illuminated as viewed from the camera position.

one where the darks and lights are distributed fairly evenly around the scene.

Alec SothCharles, Vasa, Minnesota2002

Alec SothCharles, Vasa, Minnesota2002

Would you

consider this an

average scene?

Exposing a Scene that is

Lighter or Darker than Average

Exposing a Scene that is

Lighter or Darker than Average

When you know the scene is mostly dark, you will need to adjust your

exposure with care, stopping down the exposure to catch the areas of light.

When you know the scene is mostly dark, you will need to adjust your

exposure with care, stopping down the exposure to catch the areas of light.

When metering for high contrast, do a substitute reading if you cannot get close enough to the main

subject to get a close reading.

When metering for high contrast, do a substitute reading if you cannot get close enough to the main

subject to get a close reading.

Remember: digital cameras are more prone to clipping in the light areas

than in the dark, so if in doubt, slightly

overexpose rather than underexpose a digital photograph.

Remember: digital cameras are more prone to clipping in the light areas

than in the dark, so if in doubt, slightly

overexpose rather than underexpose a digital photograph.