Ever wondered what methods professionals use when conducting a lens test? The folks over at Cinematography Database give us an inside look while testing out the new Angenieux EZ zoom lens.
Professional lens technicians mount the lens onto a lens projector (which appears very similar to the old projectors that were used back in elementary school), and the test itself is backward from how we use light to project the image onto a sensor. The light of the lens projector is used to disperse light “the wrong way” through the lens and onto a wall.
Using calibrated lens charts that are built inside of the projector, experts are able to measure, judge, and determine the major characteristics of a lens. Viewing the various frame lines on the chart will determine if a particular lens will cover a certain size sensor and whether or not it will have a vignetting effect and to what degree. The frame lines of the chart are also used to judge distortion with the focus and zoom elements of the lens.
The overall sharpness of a lens is tested by how sharp the graphics at the center of the lens are in comparison to the graphics toward the outer limits of the lens chart.
Lens technicians are able to use these tests of the lens projector to test any lens by using the lens chart as a common standard of comparison. Even though this test is used to distinguish the flaws of these lenses, that doesn’t mean that these are in fact faulty lenses. Many artists gravitate toward certain flaws in a lens as it further aids in their individual voice. Either way, lenses are our daily tools and it’s an interesting look into a side of production and testing we rarely if ever get to see.