How a Fresnel Lens Works, Explained with a Simple Blackboard Model


Do you have to’ve heard of Fresnel lenses in photos sooner than nevertheless have no idea what they’re or how they work, proper right here’s a unbelievable fast primer. On this 3.5-minute video, physicist David G. Willey (AKA the Mad Scientist) explains the science behind the lens vogue using a straightforward and easy-to-understand model on a blackboard.

Willey is a former physics instructor on the School of Pittsburgh at Johnstown, and for the previous couple of a few years, he has been explaining science by the use of physics reveals.

On this express clip from a lecture of his, Willey explains how French physicist Augustin-Jean Fresnel (1788-1827) discovered straightforward strategies to make thick and heavy optical lenses thinner and lighter.

The elemental thought is that within the occasion you scale back a parallel gap into the middle of an optical lens, gentle nonetheless enters and exits either side on the equivalent angle.

“Fresnel realized that if I’ve a really massive thick lens, it’ll nonetheless be the equivalent lens even after I take out a parallel-sided strip,” Willey says. “And if I can take out one parallel-sided strip, why not take out many parallel-sided strips?”

So within the occasion you gap out a lens with parallel strips, it’ll proceed to be the equivalent lens no matter having an air gap inside. Nevertheless this new gap lens might be pretty weak compared with a sturdy lens. The reply? Collapse the two sides collectively for a jagged, ultra-thin, lens that’s optically equal to the distinctive huge, thick, sturdy lens.

By hollowing out a sturdy optical lens with parallel slices after which collapsing gadgets from the two sides collectively, you’ll acquire a a lot thinner and lightweight lens that’s equal.

“It is a lot thinner, a lot lighter than the lens sooner than but it surely absolutely acts exactly the equivalent technique,” Willey says.

Digicam flashes and tools use Fresnel lenses to focus gentle into a narrower beam, good for maximizing gentle depth from a transportable, battery-powered system.

The enduring Polaroid SX-70 used a Fresnel lens as a a part of its difficult collapsible SLR design.

View cameras can use Fresnel lenses to help photographers greater focus and compose photos by rising the brightness of the image projected by the lens onto the digital digicam’s ground glass.

Canon and Nikon are moreover two digital digicam corporations that use Fresnel lenses to chop again the size of telephoto lenses, which can be traditionally huge and ponderous. Canon’s green-ringed Diffractive Optic (DO) lenses and Nikon’s new Phase Fresnel (PF) lenses every provide very important dimension and weight monetary financial savings compared with their typical counterparts.

Proper right here’s the inserting dimension distinction between the traditional Nikon 500mm f/4E AF-S NIKKOR FL ED VR lens and the Nikon AF-S NIKKOR 500mm f/5.6E PF ED VR:

Evaluating the sizes of the Nikon 500mm f/4E AF-S NIKKOR FL ED VR (excessive) and the Nikon AF-S NIKKOR 500mm f/5.6E PF ED VR (bottom).

While you do give up a stop of sunshine with the model new 500mm PF lens, it weighs 3.2 kilos (1.45kg) compared with the 6.eight kilos (3.09kg) of its massive sibling.

Fresnel’s title on his lens breakthrough is properly deserved, as his know-how is now used for a extensive choice of functions, from lighthouses (it’s “the invention that saved a million ships“) to cameras, lenses, and flashes used by the use of the historic previous of photos.





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