In our final post on testing and comparing HD lenses, we are going to discuss contrast.
Lens contrast
HD lens contrast is a major factor in establishing picture quality. When breaking down this topic, we find there are two essential factors that determine the contrast ratio of a lens.
The first is optical noise floor. This is determined by how the lens manufacturer manages flare and glare. If, for example, a fairly standard 2/3” camera is used with a signal-to-noise ratio of roughly 54 dB, an associated lens would need to have a contrast ratio of at LEAST 500:1; exceeding this number will offer better quality. Testing contrast ratio, while not a simple task, has become much easier by the addition of relatively new grayscale test charts.
Additionally, when testing contrast ratios in a camera/lens system on a grayscale chart, the user should optimize the camera’s settings to allow the richest and deepest levels of black. When comparing lenses, leave the previous camera settings to highlight the optical differences and limitations between the lenses.
The second factor to consider when determining contrast is a lens’ interaction with strong light sources – both direct and indirectly placed. Highlighting optical limitations and aberrations can be established by placing a direct source in front of the lens, be it studio light, the sun or hot open flame.
Using the same or similar bright light source and placing it off-axis just beyond the imaging area and panning the camera/lens system horizontally and vertically will potentially bring up similar or variants of flare and glare. At this point, a user can decide which scenarios would be most common during shooting and how the lens will perform.
We hope you enjoyed this series on testing and comparing HD lenses with the five major factors - sensitivity, resolution, color reproduction, geometrical distortion, and contrast. Do you have any other testing methods? If so, we’d love to hear about them.
To learn more about how to choose an HD lens, please visit
www.fujinon.com.