Scanner Technology: How the Lens Works

The lens is part of the scan head, perhaps the most vital part of the scanner technology. The lens is the part of the head which looks at the paper being scanned, and helps to take the perfect copy of it. The lens does not work on its own, but is part of a complicated process which includes a number of mirrors which reflect the image to the right surface. In order to understand the lens, it is necessary to understand what the scan head is, and how it works.

The Scan Head

The scan head moves across the document powered by the belt, and is held in place by a bar which prevents the scanner head from wobbling or creating a blur on the final product. The scan head is the part of the scanner which is most mobile and most easily damaged, but it is also very complicated. Inside the scan head is a series of mirrors. Different levels of scanner technology means that a scanner can have two or three mirrors, and the head reflects this by its size.

The mirrors have to be slightly curved, in order to pass the shape onto the next mirror. The item to be scanned is reflected from one mirror to another, with each mirror getting smaller, until the final mirror reflects the image into the lens. These mirrors have to be perfectly aligned in order to pass the whole image from one part to another, and once these are damaged, it is unlikely that you will be able to do anything except throw out the whole scanner and purchase a new one.

The Lens in Older Scanners

The lens itself receives the image from the final mirror. Inside this lens is a filter, which collects the image to be passed into the final scan. Older scanners may use the three pass method, where the filter collects a different color (red, blue or green) on each pass, and then creates the whole image from these three colors. In this method, the lens passes over the document to be scanned three times, which means that the whole process takes considerably longer than a print-out. The image can also be blurred where the parts of the picture have been matched up.

The Modern Scanner

Most modern scanners use the single pass, where the lens creates three small images from the large one delivered by the mirrors. Each of these images is then sent to a different color filter, so that you have a green image, a red image and a blue image, all completely different colors, yet keeping all of the detail of the original. These three images are then placed into the CCD array, which is a series of light-sensitive diodes. Once past this array, the scanner re-combines the three elements to produce the single, scanned image. This involves a lot less risk of blurring or movement between passes which the three-scan method experienced, and allows for sharper images.

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