Tuesday, September 20, 2011
Our Guide To Mirrorless Cameras
Combining compact size with the interchangeable lenses of a DSLR, mirrorless cameras offer the outdoor photographer a capable, lightweight option
Wildlife photographers need an AF system that can track moving subjects accurately, and landscape and close-up shooters need an AF system that can focus precisely where desired. Many landscape and macro photographers focus manually, so their cameras must provide accurate manual focusing, as well. All of the mirrorless cameras utilize contrast-based AF rather than the phase-detection AF used in DSLRs. The contrast-based AF systems use the image sensor itself to measure contrast, focus being most accurate when contrast is at a maximum. The contrast-based systems in early mirrorless cameras were very slow, but that has changed. Today, the top mirrorless models have improved considerably. We just tested the new Olympus E-P3 and, with its touch-screen AF, found that it focused and fired immediately upon our touching the desired point on the OLED monitor. On stationary subjects, this may well be, as Olympus claims, quicker than phase-detection AF; we're eager to get a long lens to try it on action subjects.
In Live View mode, most DSLRs use contrast-based AF rather than the quicker phase-detection systems (newer Sony models excepted), and these DSLR contrast-based systems are much slower than the AF in today's mirrorless cameras. (Sony SLT cameras utilize a translucent mirror that permits using phase-detection AF in Live View mode, even for video shooting.)
The full-time Live View operation of the mirrorless cameras also provides excellent manual-focusing capability. You can zoom in on the critical part of the subject or scene on the big LCD or OLED monitor and carefully examine the enlarged area.
Advantage: DSLRs. In bright, high-contrast conditions, a contrast-detect system is very fast, but taken across the broad spectrum of lighting situations a nature photograph is likely to face, DSLR phase-detect AF wins.
Since the mirrorless cameras get their small size in part by doing away with an optical viewfinder system, they operate in Live View mode at all times, like point-and-shoot digital cameras. This means they're harder on batteries than DSLRs, and due to their smaller size, the mirrorless cameras must use smaller batteries than DSLRs. The result is that the mirrorless cameras get far fewer shots per battery charge than a DSLR. So you'll have to buy, charge and carry more batteries with a mirrorless camera to get the same number of shots, which is something to consider for long days in the field or when traveling.
Advantage: DSLRs. Generally, DSLRs get more shots per charge.
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