What Are Diffractive Optics Lenses?
Lenses that contain so-called diffractive optic elements are becoming increasingly common, and judging by the huge number of patents surrounding the technology, it’s something that we can expect to see appearing in many more photographic lenses in the coming years. Canon has a few lenses in their lineup that contain diffractive optics, and these lenses are given the DO designation and feature a green ring around the lens barrel. Nikon call the technology Phase Fresnel, and give their diffractive lenses the PF designation, but despite the different naming conventions this is exactly the same kind of technology.
What Are The Benefits of Diffractive Optics?
Diffractive optical elements allow a lens of a specific focal length to be much shorter than a lens of the same focal length that uses a full set of more standard concave and convex lens elements. Diffractive elements can also reduce the overall number of optical elements needed in a lens, so this considerably lowers the lens’ weight too. In short, a DO or a PF lens is smaller and lighter than a standard equivalent.
How Do Diffractive Optics Work?
Chromatic aberrations occur when a lens doesn’t focus all wavelengths of light on exactly the same point. It shows itself as coloured fringing that appears around the edges of objects in an image, and is most obviously seen in areas of high contrast around the edge of a photo. Many traditional elements in a lens are there simply to correct chromatic aberrations, but a single Fresnel lens in the lens design can significantly reduce chromatic aberration, and therefore reduce the overall number of lens elements that are required in the lens design, thereby making it smaller and lighter.
Reading about this technology online can be a little confusing because Nikon continuously refers to the lens as a Fresnel lens, whilst Canon calls it a diffraction grating. You only need glance at their own explanatory diagrams though (below), to understand that they are indeed talking about the exact same thing.
Diffractive Optic Lenses on the Market Now
DO technology first joined the mainstream photography market with the launch of Canon’s 400mm f/4 DO lens way back in December 2001. Weighing in at only 4.3lbs, it was something of a marvel at the time when compared to the 11.8lb 400mm f/2.8 L IS that had been launched a year earlier. Whilst the lens was a decent performer, it didn’t quite live up to the standards that had been set by the 300mm f/2.8 L IS and the aforementioned 400mm f/2.8. It also exhibited some less than desirable circular artifacts in the bokeh. A number of wildlife photographers adopted it, but it never really achieved widespread acceptance, and neither did the 70-300mm f/4.5-5.6 DO IS that was launched around the same time.
After this initial lukewarm reception, things went quiet on the DO lens front for over ten years, presumably while Canon’s lens technicians went back to the drawing board, or waited for manufacturing technologies to catch up to their bright ideas. In 2015, the 400mm f/4 DO IS II hit the market, and this lens was a whole new ball game. Even now in 2017 as this article is being written, it’s consistently one of the hardest lenses to get your hands on because it has been so popular. Optical performance is on a par with all of Canon’s other super telephoto lenses, and the lens also exhibits some staggering performance with Canon’s extenders (teleconverters), making it an incredibly versatile lens for a huge variety of photographic applications. Canon obviously knew that they had finally perfected the DO technology because soon after this lens hit the market, a slew of DO lens patents began appearing, and they even showed off a 600mm f/4 DO IS lens that was in development.
Whilst Canon undoubtedly lead the way with their DO lenses, Nikon weren’t far behind when they launched the Nikkor 300MM f/4E PF ED in 2015. Just like Canon’s DO lenses, the Nikkor “PF” lens used diffractive optic elements to achieve the 300mm size in a much smaller and lighter package than had previously been possible. Also just like the Canon 400mm f/4 DO IS II, the Nikkor 300mm f/4E PF was heaped with praise by all the usual lens review websites. 2015 was the year that diffractive optic lenses really jumped back into the industry!