We’re often told our lenses will outlast our cameras. This holds true in almost all scenarios. “Invest in good glass” is a phrase I’ve heard time and time again. But as manufacturers hinted years ago, things change. While the sentiment is true, not all camera lenses are made of glass elements alone. Leading camera manufacturers have been using plastic and plastic hybrid elements in their consumer and professional-grade lenses for a few decades now. What makes glass the preferred choice of material for a lens element? And when does a manufacturer decide to add or exclude plastic in the construction of a lens?
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Is ‘Good Glass’ Really Just Glass?
Primary elements inside camera lenses are usually constructed of high-quality glass. Some of the inner, more minor lens elements can be plastics molded over glass, known as an aspheric hybrid type of element. Plastics are molded over an inner glass element for such lenses. Smartphone camera lenses are almost exclusively comprised of plastic elements. These tiny plastic lenses are crammed into tenths of an inch and able to focus light on high-resolution sensors. Incredible images can be created using such lenses, so what’s stopping modern DSLR and mirrorless lens manufacturers from doing the same?
History of Early Lenses
In the early years of photography, single element lenses were found to not have many practical applications. Several optical flaws like chromatic aberration meant that their usage wasn’t widespread. Charles Chevalier is acknowledged as one of the pioneers in designing and creating achromatic lenses. These were designed for the daguerreotype cameras being worked on at the time by Joseph Nicéphore Niépce and Louis Daguerre. Chevalier’s lenses were considered highly popular, even more than the famous Petzval portrait lenses by the Slovakian inventor Joseph Petzval.
Plastics in Lenses – When Did It Start?
Lens manufacturing technology began progressing rapidly, and by the early 1930s Taylor Hobson of England became the first manufacturer of telephoto lenses. In fact, renowned lens company Cooke Optics was actually an off-shoot of Taylor Hobson. On March 20, 1934, however, a gentleman by the name of Arthur William Kingston collaborated with Peter Maurice Koch de Gooreynd to form the KGK Syndicate Ltd. They first created a plastic optical lens made of Polymethyl methacrylate (PMMA) from Rohm and Haas, trademarked as Plexiglas. Koch even publicly demoed bouncing their lenses off a table to show how resistant they were to fracture.
Kingston and Koch had a fallout not long after. Their partnership dissolved over who created the first plastic lens among the two. Kingston established the optical firm Combined Optical Industries Limited (COIL) a couple of years later. They specialized in manufacturing plastic optic elements through compression and injection molding methods. COIL is still a functioning company today and positions itself as a market leader in precision low-vision products, with officers in the UK, USA, and China.
Improvements in Lens Manufacturing
By around 1937, Dupont began making its commercial version of acrylic, termed Lucite, available to industries. PMMA and its variations became widespread in lens manufacturing soon after. Early plastic models weren’t without issues, though. They easily scratched compared to their glass counterparts and were subject to discoloration easily.
Kodak began using mass-produced plastic aspheres in viewfinder optics in 1957. The first widely available camera that housed a plastic lens was the 1959 Kodak Brownie 44a. Kodak produced around 50 million Instamatic cameras with plastic lenses over the next decade.
As plastics in optics improved in quality, so did their widespread usage. In 1993, Tamron produced the first hybrid aspheric zoom lens with glass elements coated with resin. This was their Nikon mount 28-200mm f3.8-5.6 lens. “Our first-ever, and possibly the first like it in the world,” said Hank Nagashima, then-president of its United States subsidiary, Tamron Industries. Such resin coatings eliminate the traditional hours of polishing that go into making each lens element. It also helps to significantly cut down costs.
Why Do Most Smartphone Cameras Use Only Plastic Lenses?
The days of 12-megapixel resolution sensors in high-end smartphones are almost behind us. Today’s smartphone cameras have crossed the once unbelievable 100-megapixel threshold, with Samsung’s S20 Ultra boasting a whopping 108 megapixels in its primary camera. (Xiaomi’s Mi 10i also has the same resolution.) Resolving such high-resolution sensors to produce sharp images typically requires precision aspherical lenses made from optical glass. At least that’s what consumer and professional camera brands would do for their lenses. With just a few millimeters of space inside the smartphone, manufacturers turned to plastic sources as the solution for smaller, thinner lenses.
Glass vs Plastic
Plastic can be injection molded into complex shapes easily. This makes producing ultra-thin aspherical plastic elements a lot easier than glass. But glass has many superior properties to plastic: temperature stability, overall strength, resistance to breakage, and high refractive index. For camera lenses, almost every professional photographer would agree that supreme image quality is something they wouldn’t compromise. That requires good glass to produce. While plastic currently doesn’t make up the majority of most camera lenses, there is still some plastic present in them. Smartphones don’t really have much space for housing lenses, so thin plastic lenses are the only solution there.
Can’t Camera Lenses Use Only Plastic Lens Elements?
Would using all plastic elements bring down the size and weight of your favorite telephoto lens? That would be a gift to wildlife and sports photographers. Owing to their widespread demand for smartphone lenses, plastic manufacturers have been making significant improvements in the last couple of decades.
Why Do Manufacturers Prefer Glass?
However, glass is still superior to plastic for lens making in many respects. Its refractive index, temperature stability, mechanical strength, and variety are higher. This is why, even though there are some plastic elements inside a DSLR or mirrorless camera lens, plastic doesn’t make up most of it. They aren’t present in the front or rear elements of the lens. A high susceptibility to changes in shape due to humidity is not something you want in the lens element the light first comes through or the last element before the light hits the sensor. Front elements of lenses also have a lot of coatings these days. Glass elements can have a higher range of coatings applied to them as compared to plastic ones. This is due to the high transition temperature of glass. Anti-reflection coatings also tend to degrade sooner on plastics than on glass.
This is also why most smartphone cameras add a protective bit of gorilla glass or sapphire glass over the outer plastic lens element on the smartphone cameras. Glass lenses are a lot more durable as well. And they don’t easily acquire high static charges that attract dust. Lastly, plastic lenses are just not as good at transmitting light compared to their glass counterparts.
Why Use Plastic Lens Elements at All?
Much of the use of glass has to do with aspherical lens elements and their properties. By definition, an aspherical lens does not have a spherical shape. The majority of such a lens is spherical, but its edges are curved oppositely. Such elements in lenses allows for using the lens at wider aperture values and it heavily reduces the aberration spherical lenses traditionally display. It is more cost-effective for lens manufacturers to produce aspherical elements using plastic molding. This also helps keep the weight of a lens down. Manufacturers also tend to use hybrid glass plus plastic aspherical elements to improve the quality of the light they transmit. For example, Nikon has two types of aspherical lenses. The PAG (Plastics on Aspherical Glass) is the hybrid type used in some lens models.
When it comes to professional photography, you’re paying more than a pretty penny to get precision results from your lenses, which your livelihood depends on. The tradeoff of weight and size in return for high optical precision is something almost all photographers would agree to.
What’s in the Future for Lens Manufacturing and Technology?
When it comes to smartphones, it boils down to keeping the size of the lenses down in a slim device that spends a lot of time in your pocket. We’d love to see a similar kind of portability and convenience in professional cameras someday. Technological advancements in lenses for smartphones could one day be partially utilized in camera lenses too. A startup from Boston, called Metalenz, hopes to replace smartphones’ plastic lenses with silicon nanostructure waveguides. They claim their technology can one day help attach lenses directly to sensors. If this tech can be extended to compact and professional camera lenses, a day might come when sports and wildlife photographers can keep their pro gear inside their jacket pockets.
“One Metalenz can act like multiple plastic lenses, allowing the image processing software to combine images to improve image quality in the same way it combines images from separate camera modules today.”Robert Devlin, co-founder Metalenz
Because of its ability to transmit light to a sensor better than plastic, it looks like the glass is here to stay as the preferred choice for lens elements. But with technology catching up, we might see all plastic lenses producing equivalent if not better image quality in the near future.