1. Light and Exposure
Digital Photography - 2863

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

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

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

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

7. It is possible to take photographs using infrared radiation.

8. Minor White
Barns and Clouds
1955

9. Minor White used infrared film, but digital
photographers can use an infrared filter.
Road with Poplar Trees, 1955

10. 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.

11. What is “Exposure?”
Exposure = Intensity x Time

12. 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

13. In order to get a good exposure, you must be
able to ascertain the amount of light that is
hitting your subject.

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

15. There are two basic
kinds of exposure
meters:
There are external,
hand held meters...

16. and meters
built right into
your camera

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

18. Other exposure meters, called incident-light meters
measure the amount of light falling on the meter itself.

19. A hand-held exposure meter can be one that
measures either reflected or incident light.

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

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

22. In more sophisticated cameras, you can set the
controls to do more precise metering.

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

29. 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.

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

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

32. 0 128 255
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.

33. Black Middle Gray White
The graph shows how much of each tone is
captured in the photograph.

34. 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.

38. There are several
ways to use the
meter built in to
your camera.

39. Method 1:
Using a gray card

40. Gray cards can be
purchased at any
camera store.

41. 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.

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

43. With your camera set to auto or program, let
the in-camera meter suggest a possible
exposure.

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

45. “equivalent?”
more on that later...

46. Using a gray card
works well under
studio conditions.

47. A gray card is 18% gray.

48. 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.

49. 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.)

50. Method 2:
Using Histograms

51. First, you must set your camera to display the
histogram right after you have taken your
picture.

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

53. Adjust your exposure (either the shutter speed
or the aperture) manually and then retake the
picture.

54. Reading a histogram takes some practice.

55. But it can ultimately be more informative than
the actual photo that shows on your camera’s
monitor.

56. Simplified Histograms
Each of these
photographs is
correctly exposed
for the subject.

57. Method 3:
Metering for Specific Situations

58. Exposing an Average
Scene

59. What is an
“average scene?”
“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.

61. Alec Soth
Charles, Vasa, Minnesota
2002

63. Would
you
consider
this an
average
scene?

65. Exposing a Scene
that is Lighter or
Darker than Average

71. 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.

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

74. 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.