Peter Burian explains why, despite their higher initial outlays, the “fast” 70-200mm lenses can provide some important imaging advantages for serious shooters.
Because most digital SLR owners want compact, lightweight lenses, the vast majority of telephoto zooms feature a small maximum aperture. A typical 55-200mm or 70-300mm zoom is designated as f/3.5-5.6 or f/4-5.6, indicated that the maximum aperture is acceptably wide at the short end, but small at longer focal lengths. In practical terms, that translates to moderate light gathering ability, except at shorter focal lengths.
That’s fine for some shooters, but serious enthusiasts and pros prefer a wide maximum aperture with a telephoto zoom lens, such as an f/2.8 aperture. That’s because f/2.8 can transmit more light to the sensor (or film), which offers several benefits, particularly at longer focal lengths. When testing a DSLR of any brand I tend to ask for a 70-200mm f/2.8 model because a lens of this type offers advantages.
The primary reason you might want an f/2.8 maximum aperture telephoto is because it allows for shooting at faster shutter speeds. Granted, this may not be an issue on bright, sunny days, even at f/5.6 when using ISO 200, for example. In much darker locations, however, a wide aperture or “fast” lens can be a blessing. Let’s say you’re shooting a sport event…
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