A printer’s loupe & a linen tester at first glance look to be the same. When used as a linen tester threads in cloth are counted. When used as a printers loupe the magnifier reveals the quality of printed photos. A closer look reveals the difference. Read on to see pictures & more & what makes them different.
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Can You Spot the Printer’s Loupe?
It’s What You Look At That Counts!
A linen tester has a single lens, usually 25mm (1 inch) in diameter with 6 times power & ruler markings along its bottom inside edge. You count the number of threads (per inch or mm) to rate the quality of the cloth.
Checking the quality of a color image is done almost the same way but with a twist.
What Has Isaac Newton Got To Do With It?
Among his many achievements, Sir Isaac Newton is known for discovering that white light consists of many colors as shown using a prism. A magnifier lens, to a lesser degree, also behaves a little bit like a glass prism.
An equilateral prism disperses the different colors of the spectrum at slightly different angles. The red, blue & yellow dots that are used to create color images have to be printed precisely to achieve a clear image. When an image is fuzzy, a print graphics expert will look at the separation of the dots to identify the problem. This can only be done reliably if the dots are actually where they appear.
A second lens is combined with the first to correct this effect. In the top picture, you can see 3 magnifiers with double lenses which is why they are thicker. An experienced printer can measure the space between the dots & the necessary adjustments in the print process.