Thirty three years ago, back when I was ten, I had a rather peculiar hobby: holography. Long time, but I still remember the difference between Leith-Upatnieks and Denisyuk methods. And of course I know the difference between diffraction and refraction!…

…But most people, including photographers, don’t. Majority of photographers are absolutely certain that “diffractive optical element” is a fancy name for ol’ Fresnel lens (hello Ken Rockwell!).

[fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][fusion_alert type=”error” accent_color=”” background_color=”” border_size=”1px” icon=”” box_shadow=”yes” animation_type=”0″ animation_direction=”down” animation_speed=”0.1″ class=”” id=””]NB: If you have no idea what am I talking about, stop reading right now to remain more or less sane.[/fusion_alert]

Note to optical engineers and quantum physicists out there: I will be trying to explain some crazy ass science in layman’s terms. Pretty similar to how a former US Senator described the Internet as “series of tubes” and got ridiculed for it… despite the fact that his description was perfectly correct.

– Canon calls this technology “Diffractive optics“. Nikon calls it “Phase Fresnel“. How the heck it’s not a Fresnel if even Nikon calls it Fresnel?!

You see, Nikola Tesla invented great many things related to electricity, including certain generators and transformers. Your computer’s AC adaptor works on same principles. And it has coils. But can we call it a “Tesla coil“?…

Same with Fresnel and his lens. Augustin-Jean Fresnel is one of the great contributors to the theory of wave optics, but best known as the inventor of the Fresnel lens. His less known brainchild is “Fresnel diffraction”, which is a generalized theory of scalar diffraction. See the similarities to mr. Tesla and his flock of coils?

Now, watch this: Fresnel lens is a refractive optical device, not diffractive.

Refractive elements use their shape to bend the light. Diffractive optics break up incoming waves of light into a large number of waves, then recombine them to form completely new waves. In case of DO or PF elements, we basically have a hologram of the lens instead of real thing.

…Actually, judging by optical diagrams provided by Canon and Nikon, we have a hologram of the anti-lens. They use diffractive optics to cancel out chromatic aberrations by introducing holographic counter-aberrations! Damn smart.

Hopefully, my brief explanation will help clear out that widespread misconception. Diffractive optical designs are loosely based on Fresnel’s theories, but they are not “Fresnel lenses”.
[/fusion_builder_column][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][fusion_alert type=”notice” accent_color=”” background_color=”” border_size=”1px” icon=”” box_shadow=”yes” animation_type=”bounce” animation_direction=”up” animation_speed=”0.1″ class=”” id=””]This is a repost from my old personal blog. I needed some content to test the responsive layout. Besides, I’ve decided to shut down “.me” site, so saving a good old post or two seemed like a good idea.[/fusion_alert][/fusion_builder_column][/fusion_builder_row][/fusion_builder_container]