What’s a test lens?

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Test targets are patterns used to check the accuracy of optical equipment. They ensure reliability and are used to test the resolution of devices. The target must have a higher resolution than the device being tested. Test lenses are used in factory settings and by those who rely on optical instruments. Targets come in various formats and layouts, each with a specific use.

A test target is a stamped or carved pattern used to determine the accuracy of optical or electro-optical equipment. Many scientific and consumer instruments rely on optics; devices such as cameras, microscopes, spectrometers and light meters rely on lenses that must be carefully calibrated. Test lenses are used to ensure that such devices work as expected by testing their optical resolutions. They are used to ensure equipment reliability before ordinary use. Without test targets, there wouldn’t be a reasonable way to determine whether optical sensors in devices are degrading over time.

An easy way to think about a test target is to compare it to a traditional eye exam. The target itself contains models with a specified resolution; like a patient reading an eye diagram with smaller and smaller letters, the optical device under test must correctly scan the pattern on the test target, determining the boundaries between one pattern and the next. Once the optical device can no longer accurately determine the separation point between patterns, it has reached its “resolution limit.” If the resolution limit meets or exceeds the resolution limit listed for the device, the device is said to be working properly.

To successfully test the resolution of an optical device using a test target, the target itself must have a higher resolution than the device can read. Setting a higher limit than what the device should be able to achieve lets you know if it meets or exceeds your expectations for accurate perception. By trying to force the device to read a resolution it shouldn’t be able to detect, a user can determine if the device is calibrated correctly. Test lenses are employed in factory settings to ensure that new devices meet quality control standards, but they are also used by those who regularly rely on optical instruments to keep them in good condition.

A test target can come in a variety of formats. Some are printed on paper while others are on glass, quartz or white opal. Even the templates themselves come in various types; multi-bar templates and star templates are among the common layouts used. Each type of template typically has a specific use. For example, five-bar microscopy patterns are mainly used to determine the image output of cameras and lenses.




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