Digital Photography For Dummies. Julie Adair King

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СКАЧАТЬ sensor size: Full frame or smaller?

      

A photograph is formed when light passes through a lens and strikes a light-sensitive recording medium. In a film camera, the film negative performs the light-recording function. In a digital camera, the image sensor handles the task. The sensor is covered with photosites, which are electronic doodads (that's the technical term) that collect the light data needed to create image pixels.

      When you look at camera specs, the sensor type and size should be listed. Most cameras now use a type of sensor called CMOS, which stands for complementary metal-oxide semiconductor. I share that nerdy detail just so you won’t spend any more time worrying about what CMOS means. Instead, turn your attention to the sensor size, which is the critical part of the spec.

      A smaller sensor generally produces lower image quality than a large sensor. Why? Because when you cram tons of photosites onto a small sensor, you increase the chances of electronic noise that can degrade the picture. So even if two cameras claim the same resolution, the model with the larger sensor is likely to produce higher-quality images than the one with a smaller sensor.

When sensor size is presented as a single number, such as 1″, the number reflects the diagonal measure of the sensor. The photo industry also uses the following terms to refer to certain sizes of sensors:

       Full frame: The sensor is the same size as a 35mm film negative (36 x 24mm). Why full frame? The term is related to camera lenses, which are still manufactured using the 35mm film negative as a standard. That means that a full-frame sensor is large enough to capture the entire angle of view that a lens produces on a 35mm film camera. Smaller sensors can capture only a portion of that angle of view. For more on this issue, check out the upcoming section “Lens focal length.”

       APS-C (Advanced Photo System-type C): This is a smaller-than-full frame sensor but with the same 3:2 proportions as a 35mm negative. Within this category, the specific dimensions of the sensor vary from camera to camera. Nikon APS-C sensors measure about 24 x 16mm, for example, whereas Canon's typically measure approximately 22 x 15mm. Some people use the term crop sensor to refer to this category because it's a trimmed-down version of a full-frame sensor. Technically, the C in APS-C stands for classic, but crop is more helpful in remembering how these sensors vary from full-frame versions. Also, Nikon coined the term DX to refer to its APS-C sensors, using FX to indicate full-frame sensors.

       Micro Four Thirds: These sensors are slightly smaller than APS-C sensors, and as the name implies, they have a 4:3 aspect ratio as opposed to the 3:2 ratio of full-frame and APS-C sensors. Note that the term Four Thirds is used for any sensor that has a 4:3 aspect ratio, even for those much smaller than a Micro Four Thirds sensor.Which is best — 4:3 or 3:2? Well, there's no magic to either aspect ratio. But 3:2 originals translate perfectly to a 4 x 6 print, and a 4:3 image must be cropped to fit. Mind you, you also need to crop 3:2 originals to print them at other frame sizes — 5 x 7, 8 x 10, and so on. And many cameras enable you to choose from several aspect ratios for your pictures or to crop them to a certain proportion using in-camera editing tools.

      Image file format: JPEG versus Raw

      

File format refers to the type of file used to record picture data. The standard format is JPEG (“jay-pegg”), but cameras aimed at intermediate and advanced photographers usually offer a second format called Camera Raw, or just Raw for short.

Pro photographers generally prefer Raw for a couple of reasons. First, when it comes to image quality, Raw outperforms JPEG for reasons you can explore in Chapter 2, if you're interested. Second, Raw can record a greater dynamic range (spectrum of brightness values, from shadows to highlights).

      Additionally, Raw provides a higher level of creative control. JPEG files are “processed” in the camera, with characteristics such as contrast, sharpness, and color saturation tweaked to provide what the manufacturer thinks its clients like. Raw files are just that: uncooked data straight from the image sensor. The photographer then does the work of turning that data into a photo using a software tool known as a Raw converter, which gives the photographer the final say over the look of a photo.

      Don’t take all this to mean that you should bypass cameras that offer only JPEG, however. Today's digital cameras produce excellent-quality JPEG images, unlike some of the JPEG-only models of past years. But obviously, a camera that offers both formats beats one that doesn't provide the Raw option. You may not be interested in Raw now, but as your skills grow, it may become more appealing to you.

      High ISO performance (low-light picture quality)

      

A digital camera's sensitivity to light is measured in terms of ISO, named for the group that developed the standards for this attribute (International Organization for Standards). Most cameras offer a choice of ISO settings so that you can increase or decrease light sensitivity as needed. In dim lighting, for example, you may need to raise the ISO to expose the image.

Being able to increase light sensitivity is great in terms of exposure needs, but there's a tradeoff: As you increase sensitivity, you increase the chances of introducing a defect known as noise, which gives your photo a speckled look. Figure 1-6 offers an example, with the noise most evident in the dark background of the picture. Noise is also easier to spot when you enlarge the image, as illustrated by the magnified view shown on the right in the figure.

      Today’s cameras are much less noisy at high ISO settings than in years past. In fact, if you're using a camera that's more than a couple of years old, better low-light pictures is a valid reason to purchase a new model. But because noise levels at different ISO settings vary from camera to camera, check camera reviews for this important information. Bear in mind that a model that offers an ISO range that tops out at a higher number than another camera isn’t automatically better; you may not be gaining anything if the noise produced by the higher ISO is significant.

      FIGURE 1-6: Read reviews to find out how high an ISO setting a camera can use without producing noise, the speckly defect that mars this image.

See Chapter 5 to get a better understanding of ISO and how to deal with image noise.

      Lens size, type, and quality

      As with eyeglasses, having a carefully crafted lens — “good glass,” in photo lingo — is critical to image quality. Unfortunately, it's not practical for most of us to test lenses to find the best performer. The good news is that lens reviews are readily available in photography magazines and at online photography sites.

      One thing you can predict with some confidence is that a larger-diameter lens will produce sharper, better images than the tiny lenses found on smartphones and tablets. Then again, cameras that sport СКАЧАТЬ