Light and exposure


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Light and exposure

  1. 1. Light and Exposure Digital Photography - 2863
  2. 2. The area of visible light is tiny on the entire electromagnetic energy spectrum.
  3. 3. The area of visible light is tiny on the entire electromagnetic energy spectrum.
  4. 4. This narrow spectrum of visible light is what your digital camera’s sensor responds to.
  5. 5. This visible spectrum, the light that we see, rangesbetween about 400 and 700 nanometers in wavelength.
  6. 6. It is possible to take photographs using infrared radiation.
  7. 7. Minor WhiteBarns and Clouds 1955
  8. 8. Minor White used infrared film, but digital photographers can use an infrared filter. Road with Poplar Trees, 1955
  9. 9. Infrared filters block allvisible light rays and let inonly infrared radiation toreact with your sensor.You will need a longexposure time - usuallymore than a second indaylight even at yourwidest aperture - to getsatisfactory results.
  10. 10. What is “Exposure?” Exposure = Intensity x Time
  11. 11. Intensity is the amount of light thatreaches the light sensorIntensity is controlled by the apertureTime is the length of time the sensor isexposed to the lightTime is controlled by the shutter speed
  12. 12. In order to get a good exposure, you must be able to ascertain the amount of light that is hitting your subject.
  13. 13. In order to “read” the amount of light striking your subject, you need some type of exposure or light meter.
  14. 14. There are two basic kinds of exposure meters: There are external, hand held meters...
  15. 15. and metersbuilt right intoyour camera
  16. 16. Some exposure meters read the light that is reflected off your subject.
  17. 17. Other exposure meters, called incident-light metersmeasure the amount of light falling on the meter itself.
  18. 18. A hand-held exposure meter can be one that measures either reflected or incident light.
  19. 19. In your camera,the meter is calleda through-the-lens,(TTL) meter andusually measuresthe overall lightlevel.
  20. 20. When coupledwith your camerathe metercalculates whataperture andshutter speed willproduce an overalllight level thatequals middle gray.
  21. 21. In more sophisticated cameras, you can set the controls to do more precise metering.
  22. 22. Of course, how you hold the meter depends on the type of meter you are using.
  23. 23. 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.
  24. 24. One of the ways your camera helps you judge whether you are making a good exposure is by showing you histograms.
  25. 25. A histogram is a graph that shows the brightness values of all the pixels in an image.
  26. 26. 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.
  27. 27. Black Middle Gray WhiteThe graph shows how much of each tone is captured in the photograph.
  28. 28. 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.
  29. 29. There are several ways to use themeter built in to your camera.
  30. 30. Method 1:Using a gray card
  31. 31. Gray cards can bepurchased at any camera store.
  32. 32. 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.
  33. 33. Remember to capture all of the gray card when getting your meter readings.
  34. 34. With your camera set to auto or program, let the in-camera meter suggest a possible exposure.
  35. 35. Then change your camera mode to manual andchoose the settings or their equivalent before taking your picture.
  36. 36. “equivalent?” more on that later...
  37. 37. Using a gray cardworks well understudio conditions.
  38. 38. A gray card is 18% gray.
  39. 39. If you are ever in a landscape situation without a gray card, youcan use grass or green tree leaves to meter. They are very close to the 18% gray value.
  40. 40. 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.)
  41. 41. Method 2:Using Histograms
  42. 42. First, you must set your camera to display the histogram right after you have taken your picture.
  43. 43. Then after taking your first shot, check the histogram to see if you have good tonal coverage.
  44. 44. Adjust your exposure (either the shutter speedor the aperture) manually and then retake the picture.
  45. 45. Reading a histogram takes some practice.
  46. 46. But it can ultimately be more informative thanthe actual photo that shows on your camera’s monitor.
  47. 47. Simplified HistogramsEach of thesephotographs iscorrectly exposedfor the subject.
  48. 48. Method 3:Metering for Specific Situations
  49. 49. Exposing an Average Scene
  50. 50. What is an“average scene?”“average scene?”one where all the different tones whenaveraged together will equal a middle where the scene is evenly illuminatedas viewed from the camera where the darks and lights aredistributed fairly evenly around the scene.
  51. 51. Alec SothCharles, Vasa, Minnesota2002
  52. 52. Would youconsider this anaverage scene?
  53. 53. Exposing a Scene that is Lighter orDarker than Average
  54. 54. 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.
  55. 55. When metering for high contrast, do a substitute reading if you cannot get close enough to the main subject to get a close reading.
  56. 56. Remember: digitalcameras 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.