Pixels Are Like Cupcakes. Let Me Explain.
By RUSS JUSKALIAN
Published: November 12, 2008
IT happens to all of us: the moment when one finds out that more megapixels and better photographs aren’t always the same thing. To be disabused of the Megapixel Myth — this decade’s analog of the Megahertz Myth — can lead to an existential buyer’s crisis in miniature.
Disbelief, at first, gives way to a sort of embarrassing self-questioning: You mean, 15 megapixels isn’t three times better than 5 megapixels? This year’s model isn’t better than last year’s? I spent all that money upgrading — for nothing?
The panicky consumer is then faced with the choice of dumping digital electronics and becoming a Luddite, or learning about camera technology and taking control of purchasing decisions.
Upon pursuing this latter path, one soon realizes that all is not lost. Newer generations of digital cameras and camcorders, which almost always have more megapixels or higher resolutions, still tend to produce great output.
But there is more to a digital camera’s sensor than resolution. Understanding some of the basics may just convince you that, at least this year, buying last year’s model is a smart move.
Focusing on the Right Numbers
In a sea of specifications, one of the most overlooked is the size, not the number, of pixels on a camera’s sensor. Bigger sensors usually mean bigger pixels, which provides some advantages when it comes to making an image.
The mechanics of this can be understood by thinking of a digital camera sensor as a flat sheet of material pocked with millions (hence “mega”) of cylindrical, cuplike pixels. In other words, picture the digital sensor as a tiny cupcake tin.
Photons (light particles) pass through a camera’s lens and are captured by the cups in the tray. Each cup is either red, green or blue (the three colors that are the building blocks for all other colors). The more photons a cup catches, the brighter that cup’s color. Totally empty cups record black; totally full cups record white.
Larger pixels (cups, remember), with larger surface areas, capture more photons per second, which in electronics-speak means a stronger signal — and in camera-speak means less noise and cleaner colors. Bigger pixels can also capture more photons per exposure without filling up, so larger pixels hold on to their color longer and don’t go white as quickly as smaller pixels.
Since sensor sizes in compact cameras haven’t gotten much bigger, but their megapixel count has, increasing the number of pixels can be accomplished only by using smaller pixels. For this reason, it’s often not worth paying extra for the newest megapixel champion, says Phil Askey, editor of dpreview.com.
“Once you get beyond seven or eight megapixels in a compact point-and-shoot camera, the small lenses are struggling to keep up,” Mr. Askey said. “And you’re cramming so many pixels in such a small sensor that noise is becoming a real issue. We started worrying about this back in 2006, but it’s only gotten worse.”
The same thing is true for digital single-lens reflex cameras. In fact, recent tests conducted at dpreview.com concluded that the new 15-megapixel Canon EOS 50D ($1,400) “shows visibly more chroma and luminance noise,” and slightly less dynamic range, than the older 10-megapixel Canon EOS 40D ($920).
As a way to visualize just how densely packed sensors have become, Mr. Askey’s Web site provides pixel density and sensor-size data on more than 1,200 digital cameras. And while Mr. Askey cautions that buyers shouldn’t make decisions based on a single number, those data can help put a purchase in perspective alongside more comprehensive reviews of image quality.
So if you’re in the market for a “pro-sumer” D.S.L.R. (a consumer camera with the quality and features of a professional model) that minimizes noise issues, take a look at the Canon Rebel XSi ($600), Canon 40D ($920), Nikon D80 ($640), and Nikon D90 ($1,000).
Tapping Your Inner Pro
Another advantage of a larger sensor is the ability to produce images where only a relatively small portion of the subject is in focus. Completely understanding how this works may require a degree in physics, but in general, cameras with small sensors tend to produce images where almost everything appears to be in focus.
This is the main reason that, in normal shooting situations, images produced by small point-and-shoot cameras and D.S.L.R.’s look so distinct. In digital video, the result of using small sensors is sometimes referred to as the “video look.”
The bad news is that you’ll probably need to use a D.S.L.R. to produce a really shallow depth of field. The good news is you can achieve that professional look with the cheapest of entry-level D.S.L.R.’s, which are also relatively small.
(The only compact point-and-shoot options are the Sigma DP-1 for $700, which The New York Times consumer technology columnist David Pogue praised for its image quality but panned on all other counts; the new Panasonic DMC-G1, which Mr. Pogue had similarly mixed feelings about; and the newly announced, but untested, Sigma DP-2.)
If you’re looking for a smallish camera that can achieve shallow-depth-of-field images, good deals include the Canon Rebel XS (around $510 with lens), Nikon D40/D40X (around $450 with lens), and Olympus E-420 (around $460 with lens).
Skill Still Matters
Though some experts say they believe that improvement has slowed in digital imaging, it’s always wise to remember that with technology, today’s rules are tomorrow’s anachronisms.
But no matter when the next advance in digital imaging comes, the old saying that the photographer is the most important part of a good photo will still hold true.
Just consider Alex Majoli, an award-winning Magnum photographer, who is known for shooting images of war and other dramatic scenes for publications like National Geographic and Newsweek — with compact point-and-shoot digital cameras.
Or consider the more critical words of Ansel Adams.
“The sheer ease with which we can produce a superficial image,” Mr. Adams once wrote, “often leads to creative disaster.”
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