By Joe Kashi, for the Redoubt Reporter
Affordable interchangeable-lens cameras now eclipse less sophisticated point-and-shoot digital cameras and are the only type of dedicated digital camera whose sales and market share increase year by year.
That increasing popularity is largely due to the higher image quality and greater versatility possible when you purchase quality lenses that best fit your needs and budget. There’s a dark side to affordable optics, though, and that’s poor quality control. New lenses often show mis-assembly that seriously degrades sharpness. A poorly made lens used with a top-end camera will still result in lousy images that look like they were taken with the bottom of a Coke bottle.
Premium cameras with fixed-zoom lenses, such as the Canon G15 or Panasonic LX7, may show the same optical problems. In that case, though, you’ll need to return the entire camera, not just a lens, should your tests reveal unacceptable optical problems. I wouldn’t bother testing inexpensive point-and-shoot cameras. There’s no realistic expectation of decent optics on a cheap camera.
Unfortunately, mis-assembly isn’t confined to inexpensive, machine-assembled, consumer-grade lenses. Over the years, I’ve had to return a few lenses from both Pentax and Olympus, yet these vendors are among the most highly regarded lens makers, at least in their premium product lines. Published tests by major lens rental businesses even show significant variations between different samples of quite expensive prograde lenses from Nikon and Canon.
Back when top-brand lenses were hand-assembled by skilled technicians, every lens was individually tested and optimized at every step of the manufacturing process, and thus relatively expensive. Buyers reasonably expected that mis-assembled lenses would be detected and corrected at the factory. Even then, assembly variations produced both exquisitely sharp and lousy lenses from the same factory and same optical design. Rigorous quality control kept these variations within acceptable limits. Over the past several years, though, strict quality control has succumbed to market pressures forcing lower retail prices.
Some Internet-based photo retailers recognize these new realities. The most reputable dealers, particularly bhphotvideo.com and adorama.com, use a simple, no-questions-asked web-based RMA return process. That greatly reduces the hassle of returning substandard lenses for credit or exchange and is the single most compelling reason to buy solely from highly reputable, long-established dealers like these.
Now that most optical manufacturers have thrust optical quality control involuntarily upon the end user, how do you ensure that you’re getting your money’s worth? You’ll need to test every interchangeable lens and fixed-lens camera yourself to verify how well it performs in your kind of photography. Before ordering any interchangeable lens, check several lens reviews so that your expectations are objectively reasonable. I’ve found that the most thorough and comprehensive English-language lens reviews are usually found at http://www.slrgear.com (U.S.), http://www.photozone.de (Germany), http://www.ephotozine.com (UK), http://www.lenstip.com (Poland) and http://www.lensrentals.com (U.S.).
If those reviews indicate that the tested samples were not critically sharp, then there’s little reason for you to buy that lens or camera and expect better results than professional reviewers whom, I suspect, are given carefully chosen samples to ensure the best possible review. On the other hand, if reviews indicate very good to excellent results, then that’s the standard against which to measure your own purchase of that lens.
Check any new lens as soon as it arrives — you’ll have only a limited period within which to return a possibly defective lens. Although I do have lens test charts, real-world tests are easier and faster, at least for me. Besides, I rarely take photos of test charts and prefer to see how well a lens works under likely real-world circumstances.
A basic testing procedure can be fairly straightforward so long as you keep some basic skills in mind. Although a fence, rough wood or other finely detailed subject will do if you stand at a 90-degree angle when making test photos, I prefer using bare tree twigs backlit by a bright cloudy sky. This arrangement allows me to also test for good contrast, resistance to flare and chromatic aberration, as well as basic sharpness.
Do this on a calm day when small twigs are not ruffled by any breeze. The limbs should all be at about the same distance from you so that depth of field and other focus concerns do not distort your results. Aim your camera so that you have equidistant fine branches in the center and in all four corners of the frame. Focus carefully on the center of the frame.
Figure 1 shows the entire frame of such a test made using a supersharp Panasonic-Leica
25-mm Summilux lens mounted on an Olympus OM-D camera. No lens is perfectly sharp, but this one is pretty darned close, especially given its $499 average retail price.
Set your camera to its lowest ISO sensitivity and turn on image stabilization, if available. Because you’re doing this test against a bright sky, your shutter speed will likely be fast enough to prevent distorted results caused by camera or subject motion. If it’s not, then use a tripod or wait for a brighter, calmer day. Because photographing against a bright sky tends to result in underexposure that masks sharpness defects, use exposure compensation or bracketing to ensure that you have at least one good exposure in which the sky is bright and there’s detail visible on the fine twigs and buds.
Then, using aperture-priority mode, take a series of identical photographs starting with the widest aperture and reducing the aperture by 1/2 EV for every photo through at least f/8. For example, a lens with an f/1.8 maximum aperture would be tested at f/1.8, f/2, f/2.5, f/2.8. f/3.5, f/4, f/5.0, f/5.6, f/6.3, f/7.1 and f/8. By f/11, sharpness inevitably declines because of diffraction, an unavoidable physical phenomenon that shows up when small apertures are set.
Import these photos into Photoshop, Lightroom or another photo program and sharpen them to match your own practice and preferences. If possible, increase “clarity” and turn on the correction for “chromatic aberration,” the optical imperfection that results in red, blue or purple fringes around high-contrast borders, such as fine tree branches against a bright sky. These initial corrections are usually easiest in Adobe Lightroom.
If you can readily correct any slight softness, low contrast and chromatic aberration using post-processing software, then they’re really not problems nor would they be considered serious defects under modern circumstances. After these basic post-processing corrections, check every image shot at different apertures to find which apertures are sharpest.
Usually, top lenses for APS-C and for Micro Four-Thirds cameras show maximum overall sharpness somewhere between f/4 and f/7.1. Setting your camera to f/5.6 is a safe bet when working in the field. It may not be maximally sharp but is usually so close to a lens’ optimum aperture that you’re not likely to notice the difference under any foreseeable circumstances.
Modern lenses generally tend to be very sharp in the central region, but low-end and mis-assembled lenses often lose sharpness and contrast quickly toward the edges and corners of the frame. That’s why we suggest that the entire frame be filled with equidistant fine detail.
Figure 2 shows a 100 percent crop of the 25-mm Summilux’s central area. Hopefully, our newsprint reproduction shows the superb sharpness of this relatively affordable Micro Four-Thirds lens.
Figure 3 shows the left edge of the Summilux image, and it’s nearly as sharp. Figure 4, on the other hand, shows the corner of a poor-quality lens, which shall remain unnamed.
The lens used in Figure 4 is very “soft,” with blurred edges, low contrast and a lack of crisply rendered fine detail. There’s little that can be done to improve images made with this lens.
Examine every new lens for the following:
1. Is its center critically sharp at one or more apertures?
2. Are images usably sharp and crisp when set near the maximum aperture, even if not critically sharp?
3. Are the corner and edge areas generally soft and lacking crisp sharpness in the f/4 to f/8 range?
4. Is one side of the frame, such as the left or right third, always seemingly out of focal when the center and other third seem crisp and in-focus?
If you answer no to either one or two, or yes to three or four, then your new lens/camera is a prime candidate for an RMA return for exchange or refund. If you choose to return a lens for any of these reasons, state that the lens is “decentered” as your basis for returning it.
Local attorney Joe Kashi received his bachelor’s and master’s degrees from MIT and his law degree from Georgetown University. He has published many articles about computer technology, law practice and digital photography in national media since 1990. Many of his technology and photography articles can be accessed through his website, http://www.kashilaw.com.