Using Electronic and SLR Viewfinders on Digital Cameras

Some affordable digital cameras use hybrid viewfinders that work like optical viewfinders (that is, you put your eye up to a window to view your subject) but that use an electronic display to show you the image. These LCDs (liquid crystal displays) are much like the LCDs found on the backs of cameras, but they are automatically shielded from extraneous light, and are therefore much easier to view. Because they form an image using the signal from the sensor, when compared with optical viewfinders, they offer a potentially more accurate and SLR-like picture taking experience.

The SLR (single lens reflex) digital camera shows you (more or less) the exact image the sensor sees through the taking lens via an optical system. In the most common configuration, you view the subject through the lens using an image bounced off mirrors and (sometimes) a glass prism. When you take the picture, the mirror moves out of the way to expose the sensor. You lose sight of the image for a fraction of a second.

Electronic viewfinders

Poorly designed EVFs (electronic viewfinders) can be a pain to use, so you'll want to examine the view through any camera so-equipped before you sink your money into one. Here are some of the considerations to think about:

• Magnification: EVFs can suffer from viewfinder magnification issues. Because you'll be composing, and (in some cases) focusing manually via the internal LCD, make sure your view is as large and sharp as possible.

• Extended eyepoint: You might not be able to (or want to) press your eyeball up to the viewfinder window, so an EVF with an extended eyepoint is a plus.

• Readouts: EVFs usually contain a lot of information, including status readouts, grids, focus and exposure area indicators, and so forth, as shown in Figure 1. Make sure you can turn off these distracting elements when you don't want to see them.

• Swivel mount: Some eyepieces for EVFs can swivel 90 degrees to allow taking pictures from especially low or high angles.

• Resolution and size: The LCDs in EVFs typically are larger than their camera-back counterparts and have more detail. High-resolution electronic viewfinders are easier to see to discern detail and more reliable when used for focusing.

• Display rate: EVFs can have ghost images, too. A feature on some models is called smooth mode, which refreshes the EVF image 60 times a second (about twice as fast as normal), providing an especially good preview of your photo.

• Vanishing images: Obviously, the EVF can't provide a continuous image because the sensor's view must be collected and captured at the instant the photo is taken. During that interval, the image might freeze onscreen or vanish entirely. Some cameras switch into high-gain mode under dim lighting conditions, in which the image signal is amplified to provide better viewing, sometimes offering only a fuzzy or black-and-white view in that mode. Better cameras give you an accurate, full-color preview up until the exact moment the photograph is taken.

• Accurate viewpoint: EVFs don't always display 100 percent of the sensor's view. The best show at least 92–99 percent of the actual picture area in the viewfinder.

• Accurate rendition: As with any LCD, the image you see might not be exactly like your final photograph, but the results should be close.

SLR viewfinders

Both general types of SLR viewfinders use a mirror to bounce light upward, where it then reflects off a series of surfaces until the final image (erect and nonreversed from left-to-right) is viewed through an optical window. Less-expensive cameras use a series of mirrors (often called a pentamirror because of the five total surfaces in the structure), and more costly models use a solid glass prism, called a pentaprism. The latter provides a brighter, higher-contrast image that looks better and is easier to use for viewing and focusing. The light path for an image viewed by a pentamirror/pentaprism viewing system is shown in Figure 2.

Regardless of what optical or SLR viewing system you use, you want to make sure your camera either has built-in eyesight (diopter) correction to adjust for your near/far-sightedness or can be fitted with corrective lenses matched to your prescription. This vision correction enables you to get your eye close enough to the viewfinder to see the whole image. Some viewfinders make it difficult for those wearing glasses to see through the optical system because a bezel or other part of the viewfinder prevents the glasses from getting close enough.