Sunday, June 1, 2008
In the digital age, the advantages of a big maximum aperture are greater than ever
Over time, as the demand among pros and consumers shifted toward the convenience of lightweight, affordable, wide-range zooms, manufacturers responded by turning out an abundance of variable-aperture lenses. Aspherical elements, a wider use of low-dispersion glass and an overall improvement in lens design brought more quality to less expensive lenses. Then came further refinements like image stabilization, and with the digital era, higher and higher ISO equivalents delivering less and less noise and the "fix it in Photoshop" attitude. It would seem that the large-aperture or exotic lenses had slipped from the forefront of our collective attention, with the exception of only the most demanding professionals who still appreciated their merits. So, are large maximum-aperture lenses worthy of a relaunch in awareness for serious amateurs?
The answer is absolutely! Rather than being rendered obsolete by digital solutions, the advantages of fast optics are augmented or amplified, certainly not diminished, by the high-tech features of today's digital SLRs.
The speed of a lens is determined by its maximum aperture. The larger the maximum aperture, the more light the lens is able to collect and pass on to the recording medium. More light means faster shutter speeds. The dividing line between fast and not-so-fast lenses has changed over the years, but for the purposes of this discussion, we're putting that line at ƒ/2.8.
In practical use, even a one-stop difference in maximum aperture can have a meaningful effect on your ability to stop motion or work in low-light conditions. At a shutter speed of 1⁄125 sec., you can't handhold a 200mm lens, but at 1⁄250 sec., you can. That one stop makes the difference in getting the shot.
What About ISO & Stabilization?
Taking the previous example, you might be thinking, "Can't I just increase my digital camera's ISO setting and get a faster shutter speed that way?" Yes, you can, and many of the newer D-SLRs do a remarkable job of capturing low-noise images even at very high ISO equivalents. Despite this, Nikon maintains 19 lenses sporting ƒ-stops of 2.8 or larger. Canon has an astounding 33 in its lineup. Among other manufacturers, including Leica, Olympus, Pentax, Sigma, Sony, Tamron and Tokina, there are well over 100 additional lenses in this category.
We're not convinced that the improvements in sensor technology outmode the need for big, clear, light-gathering front elements with generous apertures behind them. Let's think this through—couple the ability to shoot at high ISOs with the powerful light-gathering of a fast lens, and you'll be able to work in low-light conditions that would send photographers with slower lenses home empty-handed.
As far as stabilization is concerned, you may be able to shoot handheld at shutter speeds two or more stops slower with stabilization than without it; but add on top of that the fast lens' ability to gather more light, and now you're shooting handheld in even darker conditions without a loss in sharpness. For example, compare the Canon EF 70-200mm ƒ/2.8L IS USM with the EF 70-200mm ƒ/4L IS USM. Both are Canon's top-tier L-series lenses, and both feature Canon's Image Stabilizer technology. All else being equal, the ƒ/2.8 lens is going to let you shoot handheld in a full stop less light than the ƒ/4.
Furthermore, while image stabilization does wonders for stopping the blur caused by handholding, it can't help you stop the action of your subject. Only the faster shutter speeds made possible by faster lenses can do that. So, we have to conclude that the advantages of a fast lens are amplified—not made obsolete—by new technologies.
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