The essential component of any camera is the lens, the role of which is to direct light to create images that mirror reality. Contemporary photographic lenses are sophisticated instruments comprising multiple elements (individual glass or plastic lens discs), coupled with an aperture, shutter, and controls, all organized along a central axis, and contained within the lens casing.
Minute adjustments permit an operator to regulate the quantity of light, exposure time, focus, and additional factors that influence an image’s quality. These lenses owe their complexity to a substantial history of research and experimentation to understand the behavior of light and how it interacts with different substrates— optics, in other words. This article will first review this history before previewing several innovative future lens technologies.
Standard lenses used with Radiant’s ProMetric® Imaging Colorimeters and Photometers.
A Look at Lens History
The earliest lenses were conceptualized in ancient Mesopotamia, Assyria, and Egypt, and were usually manufactured using polished crystals such as quartz.1 The Greeks were the first to establish a theory of geometrical optics. For instance, mathematician Euclid wrote a treatise, Optics, in approximately 300 B.C. Many years later, Arab mathematician Ibn al-Haytham (known as Alhazan and usually referred to as “the father of modern optics”) undertook research on pinholes, concave lenses, and magnifying glasses that was published in his Book of Optics,2 in the 10th century A.D. Alhazan also accurately explained how lenses refract light.
It remains unclear as to when the first glass lenses were conceived, although monks in the 11th -13th century are understood to have used “reading stones” for magnification. These represented “primitive planoconvex lenses, initially made by cutting a glass sphere in half.”1 Following this, during the Renaissance, the science of lenses was advanced by Galileo and Sir Isaac Newton, as well as others, as part of their research and development of telescopes for celestial observation.
The word ‘lens’ is derived from the Latin ‘lentil’ due to the similarity in shape between the legumes (left) and the optical devices (right).
Spectacles are thought to have been developed in the 1300s (possibly near Pisa, Italy). However, wearers were required to balance them precariously on their noses until the 1700s, at which point a Parisian optician integrated small rods at the sides of eyeglasses to help them to remain in place. A British optician developed this idea further by incorporating a curved section to allow the spectacles to be tucked behind the ears.3
Lens shapes comprise convex (the substrate at the center of the lens is thicker than at the edges, meaning that it outwardly curves) and concave (the substrate at the center is thinner than at the edges, meaning that it curves inwardly), with a number of variations. For instance, planoconcave lenses embody one flat side (planar) and one concave side, while biconcave lenses are concave on either side.
Lens shapes include (1) biconvex, (2) planoconvex, (3) and (6) are convex-concave lenses, also called meniscus lenses, (4) biconcave, (5) planoconcave.4
Lenses range from simple (a single layer, for example in a magnifying glass) to compound (multiple lenses aligned together, for instance in a compound microscope). The combination of multiple lenses amplifies (or ‘compounds’) the effect of each lens, augmenting magnification strength, adjusting foci, and/or correcting chromatic aberrations.
Each color (the red, blue, and green spectra of light) travels at a divergent wavelength, and every wavelength of light moves through materials (such as glass) at divergent speeds. This means that two colors of light will arrive at an identical location at divergent times, which causes image distortion. These distortions are referred to as chromatic aberrations.
The combination of lenses of different characteristics, shapes and thicknesses into compound lenses assists in correcting chromatic aberrations and helps to generate clear images with high resolution. Nevertheless, multiple lenses require a more sizable piece of camera equipment, such as a very long telephoto lens.
Chromatic aberration occurs as the red, green, and blue wavelengths of light pass through a convex lens at different speeds, resulting in different foci.
The effect of a chromatic aberration in a photographic image.
Cameras, along with some of the first photographic lenses, were not developed until the early 19th century. Over the following 100-150 years, lens technology experienced substantial experimentation and development to improve image quality, lower exposure times, and increase the capabilities of photography. Numerous lens shapes, configurations, and coatings were attempted, more sophisticated apertures and approaches were conceived, and the industry witnessed advancements, including panoramic and telephoto lenses.
In 1925, the Leica 1(A) became the first publicly available 35 mm lens camera, and it was an immediate success. Even nowadays, the 35mm lens continues to represent a staple of photography for general, professional, scientific, and industrial usage. Radiant’s ProMetric imaging photometers and colorimeters depend on 35 mm lenses, which are used as a result of the broad array of high-quality lenses available in this size. These modern lenses provide divergent focal lengths to satisfy the needs of different imaging applications and embody electronic focus capacities to supply the accuracy customers require.
Lens Technologies of the Future
Optical physicists and engineers continue to advance technology with the development of sophisticated new lens types. To illustrate, two recent steps forward in lens innovation are:
- Liquid Lenses, which utilize electrical signals to configure a drop of liquid as a means of focusing light on a film plane.5 By utilizing liquid to focus, as opposed to multiple glasses or plastic layers, these lenses can reportedly accomplish an 85% size reduction,5 as well as almost infinite variability, with no moving parts.
- Metalenses do not utilize glass to refract light, but instead use nano-fins, which are minute waveguide structures constituted by materials like titanium dioxide (as researchers at Harvard's John A. Paulsen School of Engineering and Applied Sciences utilized in their 2016 breakthrough research6). Because metalenses are flat (planar) and ultra-thin, they do not generate chromatic aberrations: every wavelength of light passes through virtually simultaneously, allowing a singular focal point.
This flat metalens is the first single lens that can focus the entire visible spectrum of light—including white light—in the same spot and in high resolution. It uses arrays of titanium dioxide nanofins to equally focus wavelengths of light and eliminate chromatic aberration.6 Photo Credits: Jared Sisler/Harvard SEAS.
Although metalenses remain in an experimental phase, researchers at Columbia Engineering have developed a flat, micron-thick lens, which is able to of correctly focus a broad range of colors of any polarization to the same focal point, without the requirement for any extra elements.7 Thinner than a sheet of paper, this category of lens has the potential to significantly lower the size and weight of optical instruments, including cameras, eyeglasses, microscopes and telescopes.
Specialty Lenses for Special Optical Measurement Tasks
Among contemporary consumer devices, displays, lighting, and electronics products, manufacturers typically utilize imaging systems for the evaluation of quality. Effective visual inspection is dependent on possessing dependable, precision lenses for capturing images with enough detail and precision to equal human visual perception, for instance for spotting blemishes on a display or surface.
Automated visual inspection technologies that depend on images for detecting defects have become commonplace in numerous industries. Nevertheless, certain categories of visual quantification and inspection cannot be performed using conventional cameras or imaging systems as a result of form factor or complex measurement angles. Radiant has conceptualized two specialty lenses to tackle these hurdles:
- FPD Conoscope Lens - The Radiant Vision Systems FPD Conoscope Lens permits high-resolution photopic quantification of the angular distribution of color, luminance, and contrast for flat panel displays (FPDs) and display components from a single point. Radiant utilizes Fourier optics, which correlate an emitting spot to a CCD, meaning that each pixel corresponds to a divergent emission angle. The conoscope lens captures a full cone of view angle data in a singular quantification to ±70 degrees. For utilization with Radiant’s ProMetric imagers, the FPD Conoscope lens yields an angular resolution of 0.05 degrees per CCD pixel.
Radiant’s FPD Conoscope Lens (left) captures a full cone of view for flat panel displays in a single measurement up to ±70 degrees. Sample of an angular plot (right), with false color to represent measured luminance.
- AR/VR Lens – The Radiant Vision Systems AR/VR Lens embodies a unique optical design that has been specially engineered for the measurement of near-eye displays (NEDs), including those integrated into virtual (VR), mixed (MR), and augmented reality (AR) headsets. The lens design can simulate the position, size and field of view of the human eye. In contrast to other lens solutions, in which the aperture is located in the lens interior, the aperture of the AR/VR lens is positioned on the front of the lens. This enables the placement of the imaging system’s entrance pupil within NED headsets at an identical location as the human eye to capture the entire immersive display.
Radiant’s AR/VR Lens (left) simulates the point of view of the human eye in an AR/VR headset to capture the full field of view of the user in a single image up to 120° horizontal (right).
From microscopes and AR eyeglasses to telescopes and lighthouses, there is no doubt that lenses in all of their diverse applications and forms shape the manner in which we “see” the world around us. Recent advancements continue to reveal possibilities for the future of technology, medicine, industry and art.
Radiant’s optical designs are engineered for capturing light and images the way users perceive them—rapidly and comprehensively. For devices that demand new optical geometries or performance, and any other advanced visual inspection solutions to evaluate product quality, contact Radiant today.
Produced from materials originally authored by Anne Corning from Radiant Vision Systems.
References and Further Reading
- “History of Optics” on Wikipedia (accessed 10/10/18) - https://en.wikipedia.org/wiki/History_of_optics
- “Alhazen” on Famous Inventors (accessed 10/10/18) - https://www.famousinventors.org/alhazen
- “Historical Timeline on Lenses, on Windhoek Optics (accessed 10/10/18) - http://www.windhoek-optics.com/index.php/2015-09-03-10-59-08/historical-timeline-on-lenses
- Image licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
- “Four Innovations that Could Revolutionize the Photography Industry” on PetaPixel - https://petapixel.com/2013/09/18/four-innovations-revolutionize-photography-industry/
- Burrows, Leah, “Single metalens focuses all colors of the rainbow in one point”, The Harvard Gazette, January 1, 2018 - https://news.harvard.edu/gazette/story/2018/01/ground-breaking-lens-focuses-entire-spectrum-of-light-to-single-point/
- “Revolutionary Ultra-thin ‘Meta-lens’ Enables Full-color Imaging, on Opli (10/3/2018) - http://www.opli.net/opli_magazine/imaging/2018/revolutionary-ultra-thin-meta-lens-enables-full-color-imaging-oct-news/
This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.
For more information on this source, please visit Radiant Vision Systems.