When Kodachrome 64 and Fujichrome Velvia 50 were the mainstays of outdoor photographers, a fast lens was a critical advantage, especially when handholding in early-morning or late-afternoon light. Lenses like the 300mm ƒ/2.8, 70-200mm ƒ/2.8, 105mm ƒ/2 and 50mm ƒ/1.4 or ƒ/1.2 were the workhorse lenses that propped up shutter speeds as light deteriorated.
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.
ABOVE (clockwise from top left):
What's A "Fast" Lens?
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.
Tokina AT-X 535 PRO ƒ/2.8 DX
The Quality (And Quantity) Of Light
Invariably, the lowest ISO setting on your camera is the setting that maximizes its dynamic range. Lower ISOs are the Holy Grail for the most complete range of tone, from shadow to highlight. Regardless of low-noise characteristics of images made at high ISO settings with some top-tier cameras, less dynamic range means images with a "flatter" look and less "pop." And, depending on the model and brand of your camera, it may not be equipped with the latest in noise-reduction technology or sensitivity to light.
Maximum dynamic range lets you achieve good results from shadows through midtones to highlights. With an evenly lit, controlled studio scene, the relatively flat light will allow you to get away with higher ISO settings. But when shooting a sunset outdoors, there's a challenging range from deep shadows to bright sky, and higher ISOs can reduce the ability of the sensor to capture the full dynamic range that it's capable of recording at lower settings.
While sensors keep getting better, you also have the option of working with some very capable noise-reduction software, two examples being Noise Ninja or Nik Dfine. It's surprising how much you can fix a photograph, but the problem with the software approach as a matter of practice rather than the occasional fix is that you're making post production work for yourself.
Aperture settings do have a meaningful effect on the quality of the image. The question arises: What's the difference between shooting an ƒ/2.8 lens at ƒ/4 or ƒ/5.6 and shooting an ƒ/4 lens at ƒ/4, or an ƒ/5.6 lens at ƒ/5.6? The adage always has been that lenses aren't at their sharpest when set at their maximum aperture, but perform their best near the middle of their range. Lenses with larger maximum apertures tend to have the middle of their range at larger ƒ-stops, so when it's not imperative to shoot wide open, there's this additional advantage.
Additionally, when you do shoot wide open, corners may be darker. Again, you can get around this in postprocessing with any number of programs that compensate for this defect, but the most efficient photographer will always opt for getting the shot right at point of capture, thereby eliminating extra work in the computer.
Olympus Zuiko Digital ED 35-100mm ƒ/2
More Fast Lens Advantages
Speed for handholding in low light is the most obvious advantage of a fast lens, but there are others worth noting that add to the user experience and the creative techniques you'll have at your disposal.
Light In The Viewfinder. For many of us, our eyes aren't what they used to be, and shooting in low light can be a strain when trying to compose in the viewfinder. Fast lenses let more light through, so you'll have an easier time seeing what you're doing.
A seldom talked about, but nonetheless potent argument for bright lenses is photographer inspiration and confidence. We find this comparable to watching a sports event through expensive light-gathering binoculars that deliver an HDTV-like big-screen view. The excitement of a rarified image is palpable, and the same is true when composing through a large-aperture lens. You have to see it to believe it.
The Depth-Of-Field Advantage. The craft of creating powerful compositions is generally a process of eliminating distraction and isolating prominent aspects of the subject or scene. This is accomplished by cropping out clutter—zooming in, changing your position or cropping the final image—but it's also accomplished by controlling the background. When you want to isolate your subject from its background, using a big aperture narrows your depth of field, allowing you to create a soft, pleasing background with fewer distractions. This effect is possible with slower lenses, but the effect is stronger and more pronounced as the aperture size increases.
Sensor Size & The Tele Advantage. Price is always a factor when talking about fast lenses. They're simply harder and more costly to make, especially when you get on the long end of the focal range.
Sony SAL-16mm ƒ/2.8 Fisheye
The magnification factor that results from the smaller dimensions of APS-sized (or sub-full-frame) image sensors is a huge benefit in this equation. Nikon's Nikkor 200mm ƒ/2 telephoto retails for around $4,000, while its Nikkor 135mm ƒ/2 telephoto retails for about $1,100. Used with any of Nikon's DX-format cameras like the D300 or D60, which magnify the focal length by 1.5, the 135mm ƒ/2 performs like a 202mm. So, you're getting the same focal length and speed of a $4,000 lens for about a quarter of the price.
Olympus has chosen to develop its system around the Four Thirds sensor that doubles the apparent focal length, thus its relatively compact $2,200 150mm ƒ/2 becomes a potent Zuiko 300mm ƒ/2, besting the capabilities of a 300mm ƒ/2.8 at twice the price and half the weight of a traditional full 35mm-film format. Matching fast lenses to the new sensors offers a staggering new set of options for going big with a smaller budget and smaller camera bag.
We've covered the benefits of fast lenses, so let's consider the drawbacks. The first is price. As we've already mentioned, price is usually a factor when talking about lens speed. Olympus offers its 14-42mm ƒ/3.5-5.6 ED Zuiko Digital Zoom lens for about $250. Compare that to its new 14-35mm ƒ/2 ED SWD Zuiko Digital Zoom lens, which goes for about $2,300—nearly 10 times the price. While it's true that there are other features in the ƒ/2 model, such as its SWD AF system, that add to the difference in price, it's a considerable leap to gain the extra speed and constant maximum aperture throughout the zoom range. But for some, when the difference between getting the shot and not getting the shot comes down to speed, the pricier, faster lens is worth every penny.
Pentax smc DA* 50-135mm ƒ/2.8 ED [IF] SDM
What's more, mating wide-angles with sub-full-frame sensors drives up the need to go wider, and it's more expensive to preserve the broad angles of view, which coupled with the added expense of larger-aperture lenses, makes going wider and brighter an expensive proposition indeed.
Another consideration with fast lenses is their size and weight relative to slower lenses. Though it's not a hard-and-fast rule, generally, a faster lens will be larger and heavier than a comparable slower lens. Sigma's 18-50mm ƒ/3.5-5.6 DC HSM weighs 8.8 ounces and measures 2.7 inches in diameter and 2.4 inches in length. Compare that to Sigma's 18-50mm ƒ/2.8 EX DC Macro HSM, which weighs in at 18.9 ounces and measures 3.1 inches in diameter and 3.4 inches in length. The weight and size increase isn't due to the speed boost alone, but it's a significant contributing factor.
Despite their more expensive price tags and relatively larger designs, fast lenses offer indispensable benefits when you absolutely need the extra light. And the new benefits of digital cameras dramatically expand the options for photographers seeking optimum quality in their photographs. Using an overused cliché, the whole is greater than the sum of its parts.