Jul 4, 2008—We recently published an article on the mysteries of camera megapixels (check it out at Megapixel). This article continues that series, discussing how to get proper exposures when shooting indoor action. Exposure defined. First, what is exposure? Exposure is the process of allowing light onto the camera’s light sensor. Good exposure is the amount of light rendering the full range of tones (lightness to darkness) that the sensor can capture. With the full range of tones, highlights run up to nearly the maximum values, which means almost completely white. In other words, a white dog or a white PVC pole should be almost completely white. The “almost” in that sentence is important. In almost every case, the whitest areas should still contain detail, such as in a white dog’s fur. When light areas are too white, that’s overexposure. At the other end of the tonal range, the darkest areas should be almost completely black. In other words, a black dog should look black but should show detail in its fur. The deepest shadows, such as on a black dog, will likely be completely black without detail, and that’s okay. When dark areas are too black, that’s underexposure. An important point: Exposure is controlled by three settings on the camera, which are discussed below: ISO (the camera’s maximum sensitivity), shutter speed, and lens opening (f/stop). Here’s an easy way to think of it: When you take a picture, it’s like filling a bucket from a hose. ISO is the water pressure inside the hose. Shutter speed is how long the hose stays running. f/stop is the diameter of the hose. Why exposure matters. It’s important to get the exposure right so that you don’t have to try to make up for it afterwards. When you shoot indoors at maximum sensitivity, you’re working right at the very limit of your digital camera’s capabilities. The more you try to make up for underexposure in processing later, the coarser, grainier, more contrasty, and harsher the image becomes. When you overexposure an image, light areas get “blown out,” and the highlights lose detail. In most cases, the detail can’t be recovered by darkening the image later. The evils of autoexposure. All cameras have autoexposure. Why not set the camera on auto and fire away? The answer is how light meters work. A light meter doesn’t know you’re photographing a white or black dog. Every light meter, from the first one to the latest one in Virgil’s Nikon D3, works the same way: It averages the light falling on it to a medium gray. So if the scene has a significant amount of light or dark, the autoexposure will be wrong. In fact, autoexposure is wrong more often than it’s right. With autoexposure, a white dog will be adjusted to be too dark (underexposure), and a black dog will be adjusted to be too light (overexposure). As you move around a ring, bright spots—window light, for example—will cause the scene to end up too dark, and shadows will cause it to end up too light. Although most arenas are fairly evenly lit, the scene changes enough—a white background wall in one place, a dark shadow somewhere else—that automatic exposure is almost always wrong. But manual exposure will work fine and be fairly consistent. It won’t be fooled by the variations in the scene. The results are far more accurate. ISO defined. ISO is the sensitivity rating on your camera. The highest ISO setting on any camera is the very edge of the camera’s capability. The higher the ISO number you can set, the more sensitive the sensor is, and the easier it’ll be to photograph indoors. Virgil’s Nikon D3 sets to ISO 6400. Many consumer cameras set to 1600. An ISO 6400 camera has four times the light sensitivity of an ISO 1600 camera. Everyone who photographs action indoors has two limits they can’t do anything about: the camera’s maximum sensitivity (ISO) and the maximum opening of the lens (f/stop). Shutter speed. To get proper exposure, you need the shutter speed that results in the full range of tones. The slower the shutter speed, the harder it is to stop action. For indoor action, Virgil uses 1/160th of a second or faster (faster means a higher number, like 1/400th). Even at 1/160th, he discards more than 50% of what he shoots, because it isn’t sharp. Camera features. Cameras have different features to help you determine when you have the right exposure: - Many cameras have a setting that shows overexposed areas on the image display at the back of the camera. Check the camera’s menu to see if there is an overexposure indicator. On some cameras, overexposed areas flash between black and white. Overexposed areas will be pure white with no detail when printed. Darkening them in Photoshop won’t add detail. Some applications like Adobe Lightroom have a unique recovery feature that can partially recover detail in areas that aren’t severely overexposed. - Many cameras have histograms. A histogram is a bar graph showing the range of densities in the scene (see examples below). The far left of the histogram is black without detail; the far right is white without detail. If you photograph a scene with a white object (a gate, a dog, a t-shirt), you shouldn’t have a big pile of data hard up against the right-hand side of the histogram. If you do, it’s overexposed. The same is true for the left-hand side, unless the scene has an area that should be completely black without detail. In almost every shot, nearly all the data should be represented in the wide midsection of the histogram. Software features. When Virgil is on location, he shoots a few test frames of scenes with a full range of tones, downloads them into the computer, and examines them using Adobe Lightroom software. Lightroom has a feature that marks overexposed highlights in bright red (shown above) and underexposed shadows in bright blue. Likewise, Adobe Photoshop has a densitometer that measures the density of the spot under the cursor, on a range from 0 (black without detail) to 255 (white without detail). Shutter speed. When shooting action, Virgil uses three exposures. One is the basic exposure that records most tones well. When an all-white dog comes to the start line, he slightly increases the shutter speed. When an all-black dog comes to the start line, he slightly decreases the shutter speed (see the black dog pictured above). Lens opening (f/stop). The wider the lens opening, the more light the sensor can receive. The lower the f/stop number, the wider the opening. Virgil’s zoom lens has a maximum opening of f/2.8. That’s pretty fast for a zoom. Fixed-length lenses are often available at f/2 or even f/1.4. f/1.4 lets in four times the light of f/2.8. Recommendations. What does Virgil recommend for getting correct exposures when shooting indoor action? Here are his suggestions: - Set the ISO sensitivity to the highest number. - Set the lens opening (f/stop) to the lowest number (the widest opening). - Use manual exposure rather than autoexposure. - Take a few test shots of scenes with a full tonal range, and examine them. If you can download them and look at them on a computer screen, that’s best. If not, use the display on the back of the camera. Then adjust the shutter speed until your exposures are correct. Use a faster speed if the image is overexposed (too light) or a slower speed if the image is underexposed (too dark). - Use the camera’s features for over- or underexposed areas. For the next article in this series, Focus on Focus, click here. Virgil welcomes questions about cameras, lenses, software, etc. If you have questions, send him an email or talk to him at a future event.Megapixel.htmlFocus.htmlmailto:Virgil@PawPrintsPet.com?subject=Exposure%20articleshapeimage_1_link_0shapeimage_1_link_1shapeimage_1_link_2
Indoor Exposure Exposé
(Article 2 in the Camera series) by Rebecca Forrest with lots of help from Virgil Sweeden