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| Nikon's Super Coolscan 5000 |
A/D CONVERTER
When a slide or negative is scanned, analog data is converted to digital by a device that is appropriately called an analog-to-digital converter. A/D converters are categorized by the number of bits used in the operation and in general, higher numbers mean that the image is rendered in more shades or gradations of each given color. Think of it as an artist's paint box: the more shades of color an artist has, the more lifelike and beautiful will be his creation.
Today's scanners use mostly 12, 14 or 16-bit A/D converters. A 12-bit converter provides 4,096 shades or increments of a color whereas a 16-bit converter delivers 16,384. That's a huge difference, but is it a difference you can see? Probably not, but if you want the best possible performance go with the 16 bit.
SPEED
Published scanner speeds are impressive but don't tell the whole story. Consider, for instance, the scanning speed of a relatively quick unit. According to the manufacturer, the Konica Minolta DiMAGE Scan Dual IV ($229 street price) scans a 35mm slide to 3200 dpi resolution in a mere 21 seconds. But that's only one step of the process. It takes time to load and unload negative carriers, transfer the digitized files into editing software, crop, color correct, resize, save -- you get the idea.
Scanner driver software that is versatile and robust can save considerable time. For example, if you launch the scanner directly (instead of as a Photoshop plug-in) the computer allocates more RAM to the scanner application, speeding up the entire process. Better scanner drivers allow you to define sets of commonly used parameters and corrections as "jobs" so that they can be saved and recalled when needed. That saves time when you're scanning several samples of the same type of film to the same resolution, for example. Also, it's usually more efficient to use the driver's presets for different film types, especially color negative film, instead of spending hours experimenting.
Transferring image files from the scanner to your computer doesn't have to be slow. A fast communications protocol like Hi-speed USB 2.0 can transfer data up to 40 times faster than USB 1.1, and IEEE1394 (Firewire to you Macintosh users) is nearly as fast. However, in the whole scheme of things, the time it takes to transfer an image is a small part of the equation.
The real time-waster is baby-sitting the machine and loading the slides or negatives. Typical slide carriers hold four pieces; negative carriers usually hold strips of six. Automatic bulk feeders are great -- but can cost half as much as the scanner itself. The Nikon Super CoolScan 5000 ED, for example, has a street price of $980. It accepts a slide feeder that will accommodate up to fifty slides at a time. If by chance your negatives are stored as uncut strips, it also accepts a roll film adapter that can handle a continuous strip of up to 40 frames. Street price of either optional accessory is $449.
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