Tuesday, June 19, 2012
Lighten Up! Go Mirrorless!
Mirrorless interchangeable-lens camera systems are a fraction of the size and weight of most DSLRs, and they can produce top-level images. What’s not to love?
By and large, mirrorless cameras use contrast-based autofocusing right off the image sensor, as opposed to phase-detection AF used by DSLRs. Contrast-based AF used to be much slower than phase-detection AF (and it still is in most DSLRs' Live View mode). But contrast-detection AF has improved considerably over the years and now rivals phase-detection in speed, although it still isn't as good as phase-detection for action subjects such as birds in flight with long lenses. On the other hand, a number of mirrorless cameras provide touch-screen AF—just touch the spot in the image on the LCD monitor where you want the camera to focus, and the camera will focus there.
There are a few interesting phase-detect exceptions. To give photographers a phase-detect option, Sony created the unique LA-EA2 Alpha NEX Camera Mount Adapter. It lets you use Sony DSLR lenses (and legacy Konica Minolta Maxxum lenses) on NEX cameras for quick, DSLR-style phase-detection AF (see the sidebar on page 71). Also, Nikon's J1 and V1 feature a hybrid AF system that uses phase-detection AF in good light and contrast-detection AF when the light is too dim for phase-detection. When the light level is bright enough, the phase-detection provides good performance on moving subjects.
Mirrorless cameras are available with sensors ranging in size from compact camera size to APS-C size. All other things being equal, larger sensors mean better image quality because they collect more light due to their larger surface areas. More light means less noise and a higher signal-to-noise ratio. The best mirrorless cameras equal the best non-full-frame DSLRs in image quality. The smaller-sensor mirrorless cameras are physically smaller in size than the larger-sensor models, but pay a price in image quality for that size advantage.
Besides image quality, the sensor size affects the angle of view of any lens. Compared to a full-frame sensor (36x24mm), an APS-C sensor has a focal-length crop factor of 1.5x so a 100mm lens on an APS-C camera frames like a 150mm lens on a full-frame camera, and a Micro Four Thirds sensor has a 2x crop factor, meaning a 100mm lens on a Micro Four Thirds camera frames like a 200mm lens on a full-frame DSLR. The CX sensor in Nikon's J1 and V1 cameras has a 2.7x focal-length factor (a 10mm lens frames like a 27mm lens on a full-frame DSLR), and the 1/2.3-inch sensor in the Pentax Q has a 5.5x factor (an 18mm lens frames like a 100mm lens on a full-frame DSLR). Mirrorless interchangeable-lens cameras that use APS-C sensors include all Samsung and Sony models, the Pentax K-01 and the Fujifilm X-Pro1. All Olympus and Panasonic mirrorless models use Micro Four Thirds sensors.
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