How to Buy a Digital Camera
In my last article, "Sense & Sensors in Digital Photography," I tried to cut through some of the mythology about image sensors and bring some sense to the subject. Today I shall explain what I look for when examining a camera for purchase. Instead of doing this in the abstract, I shall detail my thinking earlier this year when I bought my last camera, a Sigma SD-10. You will have different needs than I, but this approach ought to help you figure out what features may be important and what gadgetry to ignore. This article will also provide a detailed review of the SD-10.
Preliminary Questions — The first question to ask yourself is what you want to use the camera for. Be very specific here. The more specific you are, the easier your decision will be. I defined three uses: (1) to take portraits of friends, some to be framed and some for use as publicity photos, (2) to provide illustrations for a book I am working on, and (3) to take pictures during a month of hiking in the Himalaya. The publicity pictures and illustrations need to be of commercial quality and the illustrations require maximal flexibility. For the Himalayan shots I wanted sufficient clarity and detail that I might enlarge them to the poster size and hang them on a wall. I still owned my professional workhorse, a 2-1/4" x 3-1/4" rangefinder camera that offers all the swings and tilts of a view camera. I did not want to buy a digital camera offering less control or quality.
Once you have clarified the camera’s purpose, you can decide on the level of image sensor that you need. That was the subject of the previous article, so I shall not discuss it here. Do read it now if you have not. For me the answer was clear: I wanted either the best of the Bayer sensors or the larger Foveon.
Knowing the sensor and your purpose, you can decide on the level of camera. I put digital cameras into three categories: (1) simple point-and-shoot, (2) fully featured but compact, with a lens that is fixed to the body and cannot be swapped for another, and (3) fully featured with interchangeable lenses. I own the first and, for convenience, I would have preferred to buy the second, but to obtain the versatility and quality that I wanted, I had to buy the third. A check through the database at Digital Photography Review showed me that my choices were a Sigma SD-10 that cost $1,500 including two lenses, or models from Kodak and Canon that cost $5,000 and $8,000 for the body alone (i.e., the camera with the lenses yet to buy). I had no intention of spending more than $5,000, especially for technology that is changing so quickly and for electronic devices that usually prove impractical to repair a few years down the line. For me the choice was either the SD-10 or sticking with what I had.
Since I wanted big blow-ups that would compare to those from my 2-1/4" x 3-1/4" camera, I first checked to see whether the SD-10 could provide them. I downloaded a raw image from Sigma’s Web site, an image that appeared to be taken with a tripod and that would be a hard test of a sensor and lens, then I enlarged the image to 30" x 44" using PhotoZoom Pro (see the previous article) and had the image printed out. I could see excessive colour fringing and other flaws but they would have been correctable with software. Even without any other image-processing, the overall appearance was surprisingly good. I decided to examine the camera in person.
Three Requirements for Any Camera — I have three absolute requirements for any level of camera. The first is that all menus be labeled in English. Chinese ideograms are not memorable. When I am taking a picture, I do not want to have to look up in an instruction book what some hieroglyphics on a camera’s display are supposed to mean. If a menu isn’t in English, it might as well not be there. If all the menus are not in English, I do not want the camera, no matter how good it is, not matter how cheap it is, no matter what. The SD-10 has menus in English, so I looked further.
Second, if I am to use a camera, I must be able to see through its viewfinder. I must be able to see clearly and sharply the entire frame while wearing my glasses. Many cameras do not permit this even with simple eyeglasses, and I wear graduated lenses that are the equivalent of trifocals. The eyepiece of the SD-10 can be adjusted to let me see sharply through the portion of my glasses that I need to look through. It also lets me see the entire frame, because the viewfinder shows a lot more than the frame. This extra space is convenient for composition and is one reason I liked my big rangefinder camera. It compensates for one awkwardness: glasses make it difficult to see a digital readout that is at the very bottom of the viewfinder, below the extra space.
The third requirement is that I be able to focus the camera reliably. A camera’s focussing system affects sharpness more than almost anything else and focussing can be more problematic than it seems. Focussing looks easy in a good rangefinder camera, because lines suddenly line up, but this is merely a precise display. The display can mask any amount of error in the shape of the cam that actually adjusts the lens. A single-lens reflex camera (SLR) has no hidden mechanism – what you see ought to be what you get – but eyes are not built to focus cameras. Nobody can see the point of sharpest focus, all we can do is move the lens back and forth through that point, notice when the focus begins to get worse on either side, and try to find the midpoint. Few cameras are still made with big, bright, optical focussing systems, because electronic focussing systems are cheaper to make and easier to sell, yet most electronic devices have coarser discrimination than the eye, and they have other weaknesses as well, like motors that cannot stop instantaneously. On top of that, no automatic focussing system can know what it is that you want to focus on, all it can do is focus on the middle of the frame.
When I tried to focus the SD-10 with the cheap lens that came with it, I almost decided not to buy the camera. The small, dim image in the viewfinder did not facilitate manual focussing, and the automatic focussing did not always put the lens at the same place when I started with the lens set too close and when I started with the lens set too far away. However, after playing with the camera for a while, I concluded that when I pointed the camera at something easy to focus on, the variability in the automatic focussing was no worse than my own variability and was probably close enough, considering the depth of field. I still do not like it but I have been able to make it work. The most important factor to getting well focussed pictures has proven to be a switch on the lens that turns automatic focussing on and off. I switch it on, depress the shutter halfway to focus on what I want to, switch it off, then frame and take the photo. For maximum reliability I have learned to do this habitually. I also focus with the zoom lens extended whenever I can. I still mistrusted the system enough to buy a magnifier for the viewfinder (Nikon’s fits), but I have found it to be unnecessary. More important is a better lens that has a larger aperture and thus is brighter. Such a lens makes it easier to focus manually in light that is too dim for the autofocus.
Features, Gadgets, & Gimmicks — The criteria above are absolute requirements for me. Since the SD-10 met them, I examined it further.
One advantage of digital cameras is that you can see if your photograph is acceptable before you leave the scene – if you can see it, that is. A liquid-crystal display (LCD) on the back needs to be bright enough to be visible in bright sun. On the other hand, you need to be able to dim it enough that you can stand to use it at night. The SD-10 offers three levels of brightness, which I have found to be sufficient. The SD-10 also comes with a transparent plastic cover to protect the LCD. For taking pictures that cover stays in place but you can pop it off to use the menus.
On a digital camera, a perfect exposure will record specular reflections of the sun as pure white but will record any whites containing information that matters with enough tonality – just enough tonality – to show detail. A histogram on the LCD ought to inform you of this clearly. The SD-10 does this well. It overlays the three colour channels (red, green and blue), and if you click the + button to enlarge the image, it graphs only the enlarged portion. This approach beats any form of exposure meter hands down. I take a very quick picture without aiming, check that the highlights are properly exposed, make any necessary adjustment, then take the picture for real.
Colour slide film is designed for a range of seven f/stops between highlights and shadows that are not completely white or black. Squeezing sunlit scenes into this range can be a trick. Digital sensors need to have at least this much "dynamic range," and more is better. Much more is much better. For pictorial photography, dynamic range usually matters more than resolution. It doesn’t matter if the sensor is able to resolve fine detail on an object if you cannot see the object at all because it is buried in shadow. You can do a quick-and-dirty test of dynamic range even in a camera shop by systematically underexposing photos of a photographic grey scale. I found the dynamic range of the SD-10 to be remarkable. If highlights are correctly exposed, shadows can be 10 to 11 stops darker yet still retain some coarse detail. The pair of screenshots (linked below) from Sigma’s PhotoPro software show how easily and effectively this detail can be extracted. This photo was exposed perfectly for the highlights. The dark version shows a normal dynamic range, about what a colour slide would have shown. The light version shows additional detail in the shadows that was recorded by the sensor and brought out by the Tonal Adjustment sliders.
Although digital cameras offer you a choice of film speeds or "ISO" speeds – sensitivity would be a better term than speed – there is actually no ISO standard that can be applied sensibly to digital cameras. That’s why I am putting quotation marks around "ISO." I have never seen a credible comparison of the sensitivity or exposure-metering of two digital cameras, nor do I think it’s particularly important, since any differences are likely to be small and you can see the exposures instantly. However, I was curious to see how carefully the SD-10 was calibrated, so after I bought it, I checked it at "ISO" 100. In sunlight and in normal room light, the exposure metering on the camera agreed almost perfectly (to within 1/3 of an f-stop) with my studio exposure meter. When I photographed a scale of calibrated greys at different exposures, the correctly exposed 95-percent white was exactly where it ought to be, 2/3 to 1 stop below washing out. (Note that with a digital camera, increasing the "ISO" speed does not make the sensor more sensitive, it amplifies the signal and, at the same time, it amplifies the noise. "ISO" 100 is normal for most cameras and speeds up to 1600 are commonly available, but any speed over 400 is not likely to look very good.)
Some cameras offer a choice of metering modes – spot, segment, averaging – so you can choose the one most likely to be accurate for the picture you are about to take. This is the sort of silly featuritis that makes so many electronic devices difficult to use. There is no point to trying to figure out how to set the meter to read a scene the most accurately, it’s as fast and more certain to take a quick test picture and adjust the control that nudges the automatic exposure up or down. Automatic exposure-bracketing is almost as useless: there is rarely reason to bracket exposures when you can identify the correct exposure when you make it. The SD-10 dedicates push-buttons and primary display space to both of these "features."
Something else I can’t see worrying about is how the camera reproduces colour. As I explained in "Colour & Computers" in TidBITS-749, this is tantamount to complimenting or castigating an amoeba on its figure. There is even less reason to worry about the colour reproduction of lenses. If a lens tints the image that it projects onto the sensor, the tint will be systematic and slight, and it will be corrected automatically by whatever software converts the raw image into a usable one.
It is possible and highly desirable for a camera to compensate somewhat for camera shake by moving the sensor in the direction opposite the shake. The SD-10 does not do this. Sigma sells a telephoto lens that does, but the feature would be more useful built into the camera.
Speed of operation is a weakness with many digital cameras. They can take a long time to switch on and there can be long delays for processing the picture and writing it to memory. Check out any camera to make sure its speed is adequate for your purposes. The SD-10 responds quickly but takes long enough to process each picture that sometimes I find myself waiting for it to catch up. Fortunately, there is a workaround for this problem that is more practical than it may sound: have the camera combine two or four pixels into one, to halve or quarter the amount of data that it processes for each exposure. Although this approach reduces resolution, usually when I need to take a lot of frames quickly, I have little control over the lighting or the subject. In these situations, the overall quality of the picture is rarely optimal so the loss of resolution will never be noticed. On the SD-10, medium resolution still records as much information as can be reproduced on a full page of a glossy magazine. See the last article, "Sense & Sensors in Digital Photography," for a discussion of this topic.
Dust is the bete noire of image sensors. In almost every camera with interchangeable lenses, dust wafts into the camera whenever you remove a lens, then it lands on the sensor and creates innumerable specks in an enlargement. Preventing dust from entering the camera saves a lot of time cleaning up pictures. The SD-10 covers the opening behind the lens with a sheet of transparent plastic. Some dust manages to get on the sensor anyway but much less than the norm.
For studio photography, it is useful to be able to plug the camera into a laptop computer and see your pictures immediately at a reasonable size. The SD-10 can connect by USB or FireWire. When connected by FireWire, pictures show up in Sigma’s PhotoPro application in seconds. To light the poster linked below, I used four strobes and three halogen lamps. I found it quicker and easier to balance them and find the exposure by viewing the image than by using a meter.
Digital cameras incur hidden costs for memory cards. Price them early in your shopping. In this respect the SD-10 has a significant advantage over its competition: it stores raw images from its Foveon sensor in only one-half the space required by an equivalent Bayer sensor (see my comparison of the sensors in "Sense & Sensors in Digital Photography"). Also, writing a picture to memory can take a while and some cards are faster than others. Lexar make some of the faster cards and use some proprietary technology they call write-acceleration. The SD-10 supports Lexar’s write-acceleration technology.
Another hidden cost with digital cameras is spare batteries, especially if the batteries are proprietary. I planned to use my camera far from electricity in the Himalaya, so it had to run on disposable batteries. The SD-10 uses AA or CR-V3 batteries but it turned out that they need to be lithium cells. Despite what the manual says, other kinds don’t work. Also, I have found the SD-10’s battery life to be disconcertingly short, especially in cool temperatures.
Long before the batteries die, they act dead then come to life for a few pictures after the battery tray is removed and replaced, and they will continue do this a number of times. It looks to me as though the camera’s tolerance for both internal resistance and voltage drop are unrealistically demanding. A second pair of batteries in parallel seemed called for and can be had by buying an accessory grip/power-pack ($130) that screws onto the base. I bought one immediately upon my return from India. It adds a bit of weight and size, but in compensation, it makes the camera more comfortable to use. On the other hand, it leaves the camera wobbly on a tripod. I tried it with ordinary alkaline cells and it worked, but only for a short while. (For an explanation of how batteries fail in digital cameras, see page 9 of this discussion of battery recycling.)
For snapshots, a built-in flash is useful. Outdoors, it is often convenient to have a built-in flash to fill in shadows. I wanted one for the latter purpose especially, but the SD-10 does not have one, so I bought a Sigma on-camera unit purportedly designed for the SD-10. This flash zooms (with a scale for a 35mm cameras), bounces in all directions, and adjusts its exposure automatically. Like all such units, I find it top-heavy, gimmicky, and inaccurate. Indoors I prefer a large flash with a handle that I can detach from the camera, hold at arm’s length, and point toward a wall. Fortunately, I have not yet had to use the thing. I bought it primarily for fill light in the field but the camera’s broad dynamic range and a "Fill Light" adjustment in Sigma’s software have obviated it.
Assessing quality of construction is not high on my list because I have no idea what on a digital camera is likely to break, aside from obvious things like hinges and latches. In my experience, the structures that fail in electronic boxes are rarely visible or predictable; they are usually things like solder joints, foil traces, and the contacts of switches. If the outside of the camera is mostly plastic – well, the airplane that delivered it used a lot of plastic too, and the SD-10 does have metal innards. What gives me comfort is a camera by Kodak. The SD-10 shares many, if not most, of its mechanical parts with one of Kodak’s newest professional cameras and feels comparable mechanically. If Kodak’s camera turns out to be a hunk of junk, it will be a very expensive hunk of junk aimed at a market that values reliability above all else, so their engineers must have reason to think that Sigma know how to construct a camera.
Lenses — Most camera buffs wax expansively and expensively on the necessity of good lenses and which are the best. This strikes me as the last thing to worry about. As I explained in "Sense & Sensors in Digital Photography," the only way to tell the difference between lenses is to compare identical test photos shot on a tripod. Unless the lens has an unusual amount of colour fringing or distortion, nobody will ever look at a photo and say, "Gee, the lens you used was a dog."
That said, some lenses do produce objectionable amounts of colour fringing, especially when used on digital cameras. I don’t know why digital cameras show it more. I’ve read lots of hypotheses, but none can explain the problem completely, and digital cameras sure can show a lot of colour fringing. Look at the inset close-up of the cello’s endpin in the photo linked previously. (The upper photo shows its original state. As discussed in "Editing Photographs for the Perfectionist" in TidBITS-748, I used Asiva Shift+Gain to even out the lighting on the cello and clean up the colour fringing.) Unfortunately, this problem is exacerbated by the Foveon sensor, which can produce a fringe every bit as sharp as the line that is fringed. A Bayer sensor would be a little less sharp but a little more forgiving.
Even expensive lenses on film cameras can be freakish. I used to swear at a Leitz 90mm lens that I bought for my megabuck Leica M4s. It was sufficiently problematic that Leitz replaced it. The replacement focussed more accurately but was no better optically. To maintain contrast and to avoid artifacts from flare light (optical noise), I had to use it more carefully than any other lens I owned.
Brochures often display graphs of modulation transfer functions (MTF) that purport to summarize the optical quality of a lens. However, those graphs are the results of a simplified mathematical model. Even if you can visualize image quality from them – I certainly cannot – you will not visualize, because they do not capture, unpredictable flaws like the blue in the cello’s endpin. Neither do fancy diagrams of lens elements mean anything, nor the number of asymmetrical elements, nor the number of elements of exotic glass. The design of a lens is an art, not a science. If a lens uses a lot of elements, all you know is that the artist used a lot of paint.
I really don’t know any sensible way to compare lenses without trying them. Indeed, I don’t always know what "better" means. Imagine two lenses: when the sun is behind you, one gives a sharper picture, but when the sun is in front of you, the other one does. Which is better? Since software can correct most deficiencies, it strikes me that the most important factor is not the degree of perfection but the degree of perfectibility. Consider two marginal lenses. One is soft but consistent and can be sharpened digitally; the other is sharper but shows occasional failings that cannot be helped. I would prefer the former.
I do share the prejudice that expensive lenses are likely to be better, but "likely" is an important qualifier. Ease of production, the size of production runs, and marketing arrangements can all have significant effects on price. When I bought film cameras, I indulged my prejudice and bought only expensive lenses. I knew that this was silly – one of my Leicas’ lenses made this manifest – but I found commercial film shoots so stressful that I wanted to feel as though I was doing everything I could to minimize the risk of something’s going wrong. Digital photography is different, though. Digital images appear instantly and they are malleable. With digital cameras I cannot see any reason to buy the dubious insurance of an expensive brand name.
The most important thing to consider about lenses is not their quality but the optical perspective they provide. Imagine that you are standing a few feet back from a small window looking out at your garden. You don’t see it all but the part that you do see looks natural. Now imagine that somehow your entire garden becomes squeezed into the purview of the window. You would see everything in the garden, but the garden would look bizarre. Next imagine that the window were a photograph. The lens on the camera would have created the perspective of that photograph. A lens "seeing" the same angle as your eye would create a realistic photograph, a lens "seeing" more than your eye would create a distorted photograph.
The eye can take in a scene about 45 degrees wide without moving. When you look at an enlarged photograph, you will probably tend to hold it so that it subtends an angle of about 45 degrees around your eye. For this reason, if you are looking at an enlargement, a lens that "sees" about 45 degrees will usually provide the most normal perspective. Smaller and larger angles of view distort perspective. There is a range of what looks incontestably natural, and it is not clearly defined, but this range does not extend beyond 20-30 degrees on the narrow end or 60-70 degrees on the wide end. Narrower and wider angles of view begin to distort perspective. This distortion can be effective artistically if handled with care, but it is distortion nonetheless. Although distortion can make quite a splash, it does not usually wear well.
In round numbers, with 35mm cameras, the range of natural perspective is covered by lenses running from 30mm or 35mm to 80mm or 90mm. Nowadays, most cameras come with a zoom lens that cover this range. Often the lens will cover more than this range. Lenses that zoom over a wider range sell more cameras, so manufacturers push zoom ratios as they push megapixels. However, image quality tends to deteriorate rapidly with focal length, not for optical reasons but because longer lenses magnify the effect of a shaky hand. This problem is amplified by the small size of most digital image sensors. When you halve or quarter the size of the image, the same amount of movement doubles or quadruples the blur. I don’t want to find out from blurry pictures that I slid accidentally into a focal length that demanded a tripod, so I do not want a general-purpose lens that extends beyond the equivalent of 80mm or 90mm.
That said, if I am buying a camera with interchangeable lenses, I do want to have a lot of focal lengths available. For my SD-10 I bought additional lenses above and below the normal range. My observations of seven lenses for the SD-10 will come at the end of the article.
The Camera and the Computer — Most people think of digital cameras as optical devices, as ordinary cameras with electronic gadgetry replacing film. I think it’s more sensible to see them as digital computers, digital computers that are fed by optical devices instead of spinning disks. Some sensors feed more information than others but as I showed in "Sense & Sensors in Digital Photography," the differences are smaller than they seem. Far greater differences come with the way that the image is processed, with the way it is interpolated, balanced, cleaned of noise, and sharpened.
To convert a raw image into a usable one, a typical image-processing program will:
- Weight the colour channels to compensate for the sensor’s response to the source of light
- Set a range of brightness and contrast
- Remove portions of the image that appear to be noise
- Distort edges so that they look sharper
- Throw away information that looks unnecessary, and save the file in JPEG format
The image-processing program in a camera does all of this by default with every picture it touches. Needless to say, it cannot look at the picture and do this knowledgeably, it can only follow rules. Most reviews of digital cameras examine JPEG files produced by the cameras, so they are really not examining the quality of the optics and sensor, they are examining the results of the algorithms employed by the built-in image-processing software.
If you are satisfied with snapshots from a point-and-shoot film camera, then a digital camera’s built-in image-processing will do fine, but it will never extract the most from a picture or enable the best enlargements. You can change the camera’s settings, but a camera does not offer anything like the convenience and control of a personal computer. For me, and I suspect for many TidBITS readers, it makes more sense to buy a camera that will save files in a raw, unprocessed format, and do all of the processing afterwards on a computer.
The SD-10 is unique among digital cameras in that it does no digital processing whatsoever. To me this is a significant advantage. Not having this software built in markedly simplifies the camera’s menus. With the SD-10, it is never necessary to negotiate a complicated tree of commands with lots of hidden submenus. If I want to change the brightness of the LCD, I can see immediately how to do it. Furthermore, with the SD-10 it is not possible to lose pictures by leaving some image-processing parameter in the wrong setting.
For processing images, Sigma provides a program called PhotoPro. At first blush PhotoPro is disappointing. It looks and feels like a port from Windows, it embeds a Windows sRGB profile (see "Colour & Computers"), it hogs the CPU while idling in the background, and, incredible for a graphics package on the Mac, it does not "know" about the monitor’s calibration, so that the colour you see in PhotoPro is not the same as the colour you see in Photoshop or iPhoto or coming off your printer. Nevertheless, PhotoPro’s controls are so simple and implemented so well that I prefer it to the raw-file converter in Photoshop. (See the screenshots linked above for a look at PhotoPro’s interface.) If you want to adjust pictures individually, PhotoPro provides excellent tools, and if you want to save a folder full of files automatically as JPEGs, it can do that too. Moreover, if you also copy the raw files to your hard drive, you can always revert to them to redo something.
Summary — All in all, I think buying the SD-10 proved to be a sensible decision, considering what I wanted it for. The camera is priced for amateurs, but it feels and functions like a professional camera and I can extract pictures from it that look as though I had shot them on 2-1/4" x 3-1/4" film. I could not ask for more.
Although the SD-10 suits my purposes, it may not suit yours. I am willing to put enough time into pictures to perfect them; you may not be. If you prefer to trade time for money, a full-frame Bayer sensor will give comparable potential quality with less care. A Bayer sensor the size of the SD-10’s Foveon sensor will be a bit more limited in overall quality but more forgiving. If you have been happy with the quality of 35mm film, then you may be served just fine by a more compact camera with a smaller sensor.
Whatever you decide, if you are buying anything more than a point-and-shoot, do consider your computer alongside the camera. As I showed in "Sense & Sensors in Digital Photography," the amount of information in pictures is much less than people think. What matters to the eye is less the amount of information than how that information is presented, how clearly the information makes it through blur, grain, pixelation, and other forms of visual noise. The camera codes optical information plus optical and electronic noise; a computer decodes all of those into a visible image and removes the noise. Although this computer is usually buried inside the camera, you can use your Mac instead. Better software is available for your computer than for your camera. That is why I started this series with an article on image-processing software ("Editing Photographs for the Perfectionist," linked above). Before you buy a camera, skim that article to get an idea of what is possible and what you might be willing to do. Keep that in mind when you decide what to look for and consider the cost of the software when you shop.
Finally, for Canadian readers, I should like to add a little about buying these products in Canada. In March, 2004, I tried to find an SD-10 in a shop. I could not. While I was asking around, two salesmen warned against my buying any Sigma camera, not because of the product but because of Sigma’s Canadian distributor, Gentec International. I came to see why. Gentec never had in stock a single item that I wanted to buy or that I wanted to borrow for this review. Everything had to await delivery from Japan. Predicted delivery was sometimes weeks but more often months, and prices were higher than in the U.S., where I could buy the product off the shelf. I was expected to purchase the products sight unseen, yet they were so unusual that no shop would countenance their return for any reason. I hate to say it but the only practical vendors for these products are mail-order houses in the U.S. Not only are they faster and cheaper, they are more likely to accept returns. If you ever need to return something and recover the tax, the paperwork required is the one-page "Informal Adjustment Request" form B2G that can be downloaded from:
Supplemental Thoughts: Lenses for the SD-10 — I have tried seven lenses with the SD-10. Except as noted, all of them seem to be well constructed, but all of them tend to produce colour fringing toward the corners that is broad enough to be noticeable in enlargements if you are looking for it. Except as noted I based my judgements of sharpness on test pictures made at infinity.
The cheapest basic lens is an 18-50mm f/3.5-5.6 zoom that Sigma packages with a couple of kits. (It’s not priced on its own but adds $10 or $100 to the other items.) At 50mm this lens seems respectably sharp but at 24mm and 18mm it seems softer. The lens often shows excessive colour fringing and below 50mm it suffers from convex "barrel" distortion that is asymmetrical, so that it cannot be corrected perfectly with software. The lens feels cheaply built and is slow (dim) enough to make focussing difficult in dim light, although closing down the aperture only one f-stop brings it almost to maximum sharpness. If I spend enough time in front of the computer, I can make most of its pictures look as good as any – its images are usually perfectible – but I do not think it is comparable in quality to the camera.
In the last few months Sigma started offering an alternative, an 18-50mm f/2.8 zoom (street price $500). I borrowed one to review and decided to buy it. It shows less colour fringing, especially at 50mm, its distortion is more symmetrical, and it is sharper at 24mm and 18mm. It is maximally sharp from f/5.6 through f/11 at all focal lengths. This lens complements the camera nicely.
The cheapest telephoto lens available is a 55mm-200mm f/4-5.6 zoom (street price $140). On an SD-10, 200mm is the equivalent of 340mm on a 35mm camera. That is the equivalent of 8x binoculars. It reaches out so far that sharp pictures of distant objects require not just a tripod but also clear air without thermal currents. This lens feels so cheap mechanically that I mistrust it, but it is competent optically and is small and light. As a telephoto to carry for casual use it would be appropriate for anybody, amateur or professional. For maximum sharpness the aperture needs to be closed down two or three f-stops.
For my last article, I borrowed Sigma’s latest 50mm f/2.8 macro (street price $250). Since I had it in the house, I compared to the 18-50mm f/2.8 at 50mm. At infinity the macro lens was a little softer and more sensitive to flare. Since a macro lens is designed for close-up work, I also tested it on a copy stand. There it was a little sharper. At both distances the zoom lens showed less colour fringing. I would buy the macro only for technical work. For all pictorial photography, including extreme close-ups, I would prefer the zoom.
For a wider wide-angle lens, I bought a 14mm f/2.8 (street price $900). This lens is big and heavy. With 35mm it pushes some limits of practical optics and with the SD-10 it is a mixed blessing. When the sun is behind me, and there isn’t much white in the picture, and I am very far away from everything in the photo, it is respectably sharp from f/8 through f/16 with no more colour fringing than the usual. At distances closer than a very distant infinity, the corners soften. Where the picture contains a lot of contrast, flare light softens the image further and increases colour fringing, sometimes to remarkable amounts. Also, when the sun is near the subject, the lens tends to produce severe reflections that cannot be corrected at all. It has noticeable barrel distortion as well, although that can be corrected.
I dislike the 14mm, so for this review, I borrowed the only alternative, a 12-24mm f/4.5-5.6 (street price $670). It is even bigger and also stretches practical optics for 35mm, but it has an opposite character. Compared to the 14mm, in front-lighted, distant scenes without much white, it looks softer, but in other circumstances it looks sharper in the corners and sometimes in the centre as well. It shows similar barrel distortion but very little colour fringing and no untoward disturbance from flare light. It is more difficult to focus and slower, but it covers a wider angle and zooms through a range of focal lengths. I don’t particularly care for this lens either but I prefer it to the 14mm. When stopped down to f/11 or f/16 its softness can be overcome with Focus Magic, whereas nothing can fix some of the 14mm’s flaws. Compared to the 18-50mm f/2.8 zoom at 18mm and 24mm, the 12-24mm is usually softer but it has less colour fringing and distortion and is comparable in sharpness at f/16, which is beyond the peak of the 18-50mm. For architectural and landscape photography, to maximize depth of field I often stop down to f/16. In this circumstance I would choose the 12-24mm. I am going to replace the 14mm with this lens, but I am also going to hope that Sigma come out with a 12mm or 14mm lens that is designed for the SD-10 and works better.
The 15mm fish-eye (street price $450) is of modest size although it, too, is designed to cover 35mm film. On an SD-10 it covers only a little more than the 14mm lens but it provides a unique perspective. It is a fish-eye perspective, so that straight lines end up curved, but only the central portion of the image is captured on the small sensor of the SD-10, so the curvature is not severe. On the other hand, unlike an ordinary wide-angle lens, it does not magnify objects near corners and it does not distort any angles. This means that for scenes containing no straight lines, the lens provides a more natural perspective. The difference is subtle but to my eye it is significant. I carried this lens and the 14mm in the Himalaya. I rarely used the 14mm, but I used this one often. It’s maximally sharp from f/5.6 through f/11 and is the sharpest of the three wide-angle lenses.
None of the wide-angle lenses accepts a filter in front; they accept only gelatin filters in back, but that is of little consequence. With all digital cameras, software supplants colour-balancing filters and I was pleasantly surprised to find that with the SD-10, software also supplants polarizing filters for their primary use, which is to increase the saturation of colours that are washed out by the glare of the sun. (I don’t know about polarizers with other digital cameras, because I don’t know why they aren’t necessary on the SD-10.) On the SD-10, the only use I have found for a polarizing filter is to reduce patterned reflections off windows and water, but that use is more common in photography books than in the field.
All of these lenses can be fitted to many cameras besides the SD-10 but I have no idea how they would work on any other camera. The optical characteristics of an image sensor interact with the lens in so many ways that I do not know how to divorce the two.
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