memobug
October 17th, 2002, 04:23 PM
Erratic, under or overexposure is a common complaint of digital cameras. This is far from the last word on exposure
The basis of the exposure problem is that the CCD or CMOS sensor in a digital camera is much less forgiving at image capture than most users have experienced with even inexpensive cameras using color negative film.
The exposure range and experience is much more akin to what you'd see using a slide film. A moderate amount of overexposure can result in blown out highlights.
The metering system in most modern cameras is based on a system of averaging, and it is a difficult job to make an evaluation of overall scene brightness and determine an exposure that will give acceptable results in both highlight and in shadow. No system can produce acceptable results 100% of the time.
The various modes take into account the brightness portions of the subject frame - matrix metering samples a number of areas, center weighted metering concentrates on the intensity of the centermost portion, and spot metering in theory measures only a tiny portion of the center of the frame.
The photographer also has a a choice of metering programs. Aperture priority lets him select an aperture and have the camera calculate an appropriate shutter speed. Shutter priority lets the photographer select a shutter speed and have the camera choose the aperture. Program mode lets the camera make a few recommended shutter and aperture settings and lets the photographer choose among them. But all these modes are based on a perception of the world as having limited contrast with everything averaging out to a meterable exposure.
If only the world worked that way! If we limited ourselves to photography of red barn doors, grassy green fields and blue sky, or (Kodak Grey cards for that matter), there would probably be no issue. But we want sunsets and backlit subjects, white snow and black cats, and we want them all to register perfectly with tone and detail.
And if this weren't enough, we have the exectation that if we add a flash unit to the top of the camera (or pop up the fill flash unit) The resulting exposure will be perfect. T'aint so.
The other day on another forum, a photographer complained that his S2 was underexposing. He had set up a nice white backdrop and attempted to photograph some batteries in front of it. The camera doesn't have the same perception of the scene. It's programmed to average that background to a middle grey, so the result was a nice grey backdrop and underexposed batteries.
Advances in technology like the D-series lenses can communicate information about subject distance to the camera so that the flash unit can help achieve proper exposure, but these systems are not 100% effective.
What can you do?
USE THE TOOLS
Learn to use the histograms, which are the best tool available for assessing exposure Use the exposure adjustment buttons on the flash and camera to fine tune exposure for different situations of backlight and subject color.
Recognize that with a digital camera it is usually better to slightly underexpose a scene than to overexpose it. Detail that is lost to overexposure is gone forever, but a lot of shadow detail can be recovered by using the Histogram or Levels control in your image program. Try using the bracketing feature to take several exposures of the same scene.
REDUCE SCENE CONTRAST
Use fill flash in sunny conditions or whenever you have a lot of contrast in a scene. The popup flash works great up to 8 feet or so. Set it for -1.5 or so and it will help eliminate the racoon eyes and reduce the contrast in the scene.
Recognize when a scene has too much contrast to be successfuly recorded. Adjust your metering to capture the tonal range of interest, modify the scene by adding more light into the shadows, or find yourself another scene. Experiment with photography at noontime on sunny day vs. an overcast afternoon.
TAKE CONTROL!
Try shooting in Manual mode to learn more about how the camera (and electronic "film") register a scene. The camera sees much more contrast than you perceive with your eyes.
Experiment with the tone setting on your camera. Try taking the same photo in several TONE settings to see the difference in how they record. We are very fortunate in the S2 world to have the histogram, Tone and color controls right at our fingertips.
Shoot in standard TTL mode. It is often more predictable than matrix balanced modes which use fuzzy logic and can be difficult to understand
For advanced photographers, experiment with image capture in the RAW format. More detail will be recorded and you will be able to capture more dynamic range in your photos at the expense of some postprocessing time and larger files at capture time.
The basis of the exposure problem is that the CCD or CMOS sensor in a digital camera is much less forgiving at image capture than most users have experienced with even inexpensive cameras using color negative film.
The exposure range and experience is much more akin to what you'd see using a slide film. A moderate amount of overexposure can result in blown out highlights.
The metering system in most modern cameras is based on a system of averaging, and it is a difficult job to make an evaluation of overall scene brightness and determine an exposure that will give acceptable results in both highlight and in shadow. No system can produce acceptable results 100% of the time.
The various modes take into account the brightness portions of the subject frame - matrix metering samples a number of areas, center weighted metering concentrates on the intensity of the centermost portion, and spot metering in theory measures only a tiny portion of the center of the frame.
The photographer also has a a choice of metering programs. Aperture priority lets him select an aperture and have the camera calculate an appropriate shutter speed. Shutter priority lets the photographer select a shutter speed and have the camera choose the aperture. Program mode lets the camera make a few recommended shutter and aperture settings and lets the photographer choose among them. But all these modes are based on a perception of the world as having limited contrast with everything averaging out to a meterable exposure.
If only the world worked that way! If we limited ourselves to photography of red barn doors, grassy green fields and blue sky, or (Kodak Grey cards for that matter), there would probably be no issue. But we want sunsets and backlit subjects, white snow and black cats, and we want them all to register perfectly with tone and detail.
And if this weren't enough, we have the exectation that if we add a flash unit to the top of the camera (or pop up the fill flash unit) The resulting exposure will be perfect. T'aint so.
The other day on another forum, a photographer complained that his S2 was underexposing. He had set up a nice white backdrop and attempted to photograph some batteries in front of it. The camera doesn't have the same perception of the scene. It's programmed to average that background to a middle grey, so the result was a nice grey backdrop and underexposed batteries.
Advances in technology like the D-series lenses can communicate information about subject distance to the camera so that the flash unit can help achieve proper exposure, but these systems are not 100% effective.
What can you do?
USE THE TOOLS
Learn to use the histograms, which are the best tool available for assessing exposure Use the exposure adjustment buttons on the flash and camera to fine tune exposure for different situations of backlight and subject color.
Recognize that with a digital camera it is usually better to slightly underexpose a scene than to overexpose it. Detail that is lost to overexposure is gone forever, but a lot of shadow detail can be recovered by using the Histogram or Levels control in your image program. Try using the bracketing feature to take several exposures of the same scene.
REDUCE SCENE CONTRAST
Use fill flash in sunny conditions or whenever you have a lot of contrast in a scene. The popup flash works great up to 8 feet or so. Set it for -1.5 or so and it will help eliminate the racoon eyes and reduce the contrast in the scene.
Recognize when a scene has too much contrast to be successfuly recorded. Adjust your metering to capture the tonal range of interest, modify the scene by adding more light into the shadows, or find yourself another scene. Experiment with photography at noontime on sunny day vs. an overcast afternoon.
TAKE CONTROL!
Try shooting in Manual mode to learn more about how the camera (and electronic "film") register a scene. The camera sees much more contrast than you perceive with your eyes.
Experiment with the tone setting on your camera. Try taking the same photo in several TONE settings to see the difference in how they record. We are very fortunate in the S2 world to have the histogram, Tone and color controls right at our fingertips.
Shoot in standard TTL mode. It is often more predictable than matrix balanced modes which use fuzzy logic and can be difficult to understand
For advanced photographers, experiment with image capture in the RAW format. More detail will be recorded and you will be able to capture more dynamic range in your photos at the expense of some postprocessing time and larger files at capture time.