The term "pro lens" gets tossed around a lot in nature photography circles, but what exactly does it mean? What makes one lens fit for pros while another is relegated for amateur shooters? Which is really best for you and your style of photography?
Generally, pro lenses deliver better optical performance than lesser lenses, quicker and more accurate autofocusing, and are more ruggedly built. They also offer the fastest maximum apertures, so you can use lower ISO settings or shoot in dimmer light. On the downside, pro lenses tend to be much bulkier than consumer lenses, and usually they cost considerably more.
Consumer lenses are the opposite: Generally, they're not as sharp, have more distortion, don't autofocus as quickly or accurately, and are slower and so require higher ISO settings or brighter light. But the consumer lenses are capable, and also much more compact and much less costly, thus enabling photographers who don't have pro budgets to have access to a wide range of focal lengths. Often pros use them when they want to travel light.
We'll break down the key features and characteristics to help you make the best decisions when choosing your lenses of choice. The results might surprise you.
Pro lenses perform better than consumer models largely because the pro lenses have superior optical designs and elements. While extra-low-dispersion and aspherical elements can be found even in $500 consumer superzooms, the ones found in pro lenses tend to be of glass rather than plastic and are more precisely manufactured. The pro lenses are better constructed to tighter tolerances and are less likely to be troubled by production flaws than mass-produced consumer optics. This is not to imply that consumer lenses are not good, just that pro lenses are frequently better.
Pro lenses also provide more superior AF performance than consumer lenses, because the pro items use quicker, more powerful AF motors and processors and more effective AF algorithms. To keep cost down, consumer lenses use less-capable AF motors and internal processors. Again, this is not to say consumer lens AF performance is not good, just that the pro lenses are typically faster.
The Canon EF 300mm f/2.8L IS II USM pro supertelephoto lens measures 5.0x9.8 inches and weighs 5.2 pounds. Canon's EF 300mm f/4L IS USM consumer supertele measures 3.5x8.7 inches and weighs 2.6 pounds. (We're singling out Canon here, but the relationships are pretty much the same for other brands.) That means the consumer lens is hand-holdable for most people, while the 300mm f/2.8 is not. We know people who hand-hold the 300/2.8, including normal-sized ladies, but most photographers will not enjoy doing that.
F/2.8 is a stop faster than f/4 – not much for some situations, but it means in a given light level you can set one-stop lower ISO, or use a shutter speed twice as fast, with the f/2.8 than with the f/4 lens. Mid- and high-end DSLRs also have AF systems that can deliver higher focusing accuracy with f/2.8 lenses than with slower ones. That has nothing to do with brightness, but rather with the wider "base" of the f/2.8 AF sensor. The wider aperture also limits depth of field more, handy when doing selective-focus images to concentrate the viewer's attention on a specific portion of a subject.
All-in-one zooms—those 18-200mm to 18-300mm wide-range wonders—offer the benefits on wide-angle to telephoto focal lengths in a single package, close focusing, compact size and low cost. And for these reasons, you probably should have one in your lens collection—especially if you travel.
So what's the downside? Well, it's all but impossible to completely correct for all possible aberrations, distortions and the like for a wide range of focal lengths in a single lens. So the all-in-one zooms tend to show more distortion and aberrations, and less sharpness and contrast then prime lenses, or shorter-range zooms. The wide-range zooms also tend to be on the slowish side—f/3.5 at their widest focal length down to f/5.6 or f/6.3 at their longest. But most these days incorporate image stabilization, which helps offset the slower maximum apertures, especially with stationary subjects.
Bottom line: You're not going to get the most out of your 50MP EOS 5DS or 36MP Nikon D810 with a $500 consumer 18-200mm zoom, but when you want to be ready to handle just about any subject that comes along quickly while traveling light, you can't beat the all-in-one zoom.
A faster lens also provides a brighter viewfinder image, making it easier to compose photos and focus manually, especially in dim light. In live-view mode, a faster lens can deliver a less-noisy live image.
Of course, a faster lens needs a larger front element, which makes for a bulkier and more costly lens. And it's more difficult to correct all aberrations and distortions in a faster lens, so sometimes a pro f/4 lens will be sharper than its f/2.8 counterpart.
The Supertele Zooms
We now have three 150-600mm supertelephoto zooms, two selling for just over $1000 (Sigma 150-600mm f/5-6.3 | C and Tamron SP 150-600mm f/5-6.3), the other for just under $2000 (Sigma 150-600mm f/5-6.3 | S). That's a whole lot more affordable than the $9700-$11,500 for 600mm lenses from the major DSLR manufacturers, bringing lots of supertelephoto reach to a lot more photographers. Of course, the zooms do not match the costly pro 600s in optical or AF performance, but they are surprisingly good for the cost, much less bulky, and focus closer, which can be an advantage when a bird lands on a branch 10 feet away.
Pro lenses are constructed with the best materials, like space-age metals and exotic glass. Their rugged designs are well-sealed against moisture and dust. Consumer-level lenses typically contain more plastics in the barrels and elements, and are less rugged, with little to no moisture resistance. Pro lenses will hold up better under heavy use in tough field conditions. Of course, if you don't put your photo gear to hard use, this is less of a concern. Note that "weather sealed" lenses and camera bodies are not warranted against water damage, but the pro units tend to "weather" the elements much better than the consumer products.
The Prime Lenses
The word "prime" means "extremely good," so who wouldn't want prime lenses? Well, prime in lens talk means single-focal-length, as opposed to zooms. It's much easier for lens designers to correct aberrations and distortions for a single focal length than for a whole range of focal lengths, so primes tend to be sharper and more free of distortions and aberrations than zoom lenses. Pro prime lenses tend to be even sharper, better built and have better AF performance. But a series of prime lenses costs a lot more than one to three zooms, takes up more space in your camera bag, weighs a lot more, does not provide the in-between focal lengths you get with the zoom, and means you have to change lenses more often—which takes time in the heat of the moment, and means more opportunities for dust to enter the camera and settle on your sensor assembly.
If you have one or two favorite focal lengths, it's probably wise to buy primes of those lengths (especially wide-angles) for optimal image quality, but you should also have a zoom or two to cover other lengths you sometimes need. To get the coverage provided by an 18-200mm zoom, you'd need 18mm, 21mm, 24mm, 28mm, 35mm, 50mm, 85mm, 100mm, 135mm and 200mm primes—and you still wouldn't have the in-between focal lengths.
Camera or Lens?
With both DSLRs and lenses, newer is better than older, and higher-end is better than lower-end. So if your budget only allows for one, is it better to get a better camera or a better lens? In terms of a given generation of technology, a better lens with a lesser camera will show more visible benefits than a better camera with a lesser lens. This was especially true in the film days, when all cameras used the same "image sensor"—the film. With digital, each new generation of cameras offers improved image quality due to sensor improvements. So if your DSLR is two or three generations old, you'll probably be better off getting a new camera than a new lens, in terms of image quality. But if you're talking the same-generation, choose a new lens: In reasonably bright light (i.e., at lower ISO settings), the $1700 Canon EOS 7D Mark II with the $6099 EF 300mm f/2.8L IS II USM pro lens will deliver better image quality and AF performance than the $5299 flagship EOS-1D X with the $1349 EF 300mm f/4L IS USM lens (not to mention, more "reach" for bird/wildlife photography). At higher ISO settings, the EOS-1D X's better full-frame sensor offsets much of that advantage, though.
The 3-Zoom Kit
Quite a few pro photographers carry a three-zoom kit: 24-70mm and 70-200mm f/2.8 or f/4 (for full-frame; 16-50mm and 50-135mm or thereabouts for APS-C), plus a wider 16-35mm or longer 200-400mm, depending on the particular photographic specialties (e.g., landscape or wildlife). This yields an optical arsenal that can cover pretty much any needs, with good quality and the kit can be carried fairly easily.
Another consideration, of course, is your need for a given focal length. If your longest lens is 70mm and you want to start photographing birds, you'll be better off buying a long lens than a new camera body even if you don't have the "latest and greatest" body.
Most manufacturers publish MTF (Modulation Transfer Function) curves for their lenses. These show how well the lens reproduces the contrast and resolution of an original test chart. The horizontal axis shows distance from the center of the image (the center is at the left edge of the horizontal axis, and the extreme edge of the frame at the right), while the vertical axis shows what percentage of the original test target's contrast is maintained. MTF charts usually show curves for different lines per millimeter (the lower ones—for 10 lpm, for example—are indicative of how much contrast the lens can deliver, while the higher ones—for 30 or 40 lpm—are good indicators of how much resolution the lens can deliver. There are also dashed lines, which indicate performance for lines running parallel to the lens radius (sagittal), and for lines perpendicular to those (meridional); these indicate the degree of astigmatism present.
The main things to keep in mind are that higher and straighter are better. The higher the lines are on the MTF chart, the better the contrast and sharpness. The straighter the lines, the more consistent the lens's performance across the image frame. Also, the more parallel the line pairs are to one another, the better the bokeh (diverging line pairs indicate astigmatism, and less attractive bokeh).
MTF charts are generally for the lens at its widest aperture; with most lenses, performance increases as the lens is stopped down a stop or two. For zoom lenses, separate charts are provided for the shortest and longest focal lengths and sometimes an intermediate focal length.
Another important thing to keep in mind about MTF charts is that in most cases, they are hypothetical, calculated from how the optical formula should perform, rather than measured with actual lenses. Imperfections in lens elements, mechanical as well as optical, and production tolerances mean a lens seldom will perform quite as well as the MTF chart indicates. But the MTF charts do let you compare the predicted performance of lenses you're contemplating for your kit.
There are also curves that plot MTF (percent contrast) against frequency (lpm). MTF50 curves, which show what percentage of the test target's contrast the lens can reproduce at different lpms—MTF50 being the resolution at which the lens can deliver 50% of the test target's contrast.