Lensa utawa uga diarani Kanta yaiku siji srana kang awujud kaca bening gepeng kang duwé sisih-sisih kang simetris. Lensa mono duwé kagunan kanggo ngumpulake cahya marang siji titik utawa malah nyebarake cahya kang liwat ing tengahé. Lensa sepisanan dipangerteni saka catatan sandiwara Yunani Kuno liwat cathetane Aristhophane The Clouds (424 SM) kang mratélakaké anané istilah gelas-gelas pembakar (lensa cembung kang kanggo mokusake sinaring srengéngé kanggo nyipta geni) ing karyané. Wong kang nemu téyori babagan lensa sepisanan tur uga mratelakake kadadéan bayangan ana ing retina yaiku fisikawan muslim saka Arab kang asmane Alhazen (Abu Ali al-Hasan Ibn Al-Haitham)

Lensa kapérang dadi manéka jinis. Lensa bisa dibédakaké saka wujud sisih-sisine. Kontruksi lensa kang paling umum tinemu yaiku lensa speris, yaiku lensa kang sudut mlengkung lumah bidange dibandingake karo radius speris. Titikan radius kang digunakaké dilambangake kanthi lambang R,kang bakal duwé nile positif nalika saben sisine mlengkung ngadohi titik pusere lensa,lan sinebut antarmuka cembung.

Kontruksi lensa kang paling akèh yaiku kang awujud lensa speris, yaiku lensa kang duwé babagan speris (mlengkung),notasi kang digunakaké yaiku R.

Wikimedia Commons duwé médhia ngenani Lens.

• Lens article at digitalartform.com Archived 2016-03-04 at the Wayback Machine.
• Thin Lens Java applet
• Article on Ancient Egyptian lenses
• Lighthouse Getaway: Fresnel lens (contains photographs.)
• Pepper, Terry. "Seeing the Light: Lighthouses on the western Great Lakes".
• Random Destructive Acts via Focused Solar Radiation. Archived 2010-01-18 at the Wayback Machine.
• TruckView Fresnel lens combats the HGV Blind-Spot. Archived 2019-04-08 at the Wayback Machine.
• How the Fresnel lens works.
• A computer analysis of the Fresnel lens cross section depicted in the 'graphic examples' section of this very Wikipedia article. Archived 2009-05-20 at the Wayback Machine.
• Applied photographic optics Book
• Book- The properties of optical glass
• Handbook of Ceramics, Glasses, and Diamonds
• Optical glass construction
• History of Optics (audio mp3) by Simon Schaffer, Professor in History and Philosophy of Science at the University of Cambridge, Jim Bennett, Director of the Museum of the History of Science at the University of Oxford and Emily Winterburn, Curator of Astronomy at the National Maritime Museum (recorded by the BBC).
• a chapter from an online textbook on refraction and lenses Archived 2009-12-17 at the Wayback Machine.
• Thin Spherical Lenses on Project PHYSNET.
• Lens article at digitalartform.com Archived 2016-03-04 at the Wayback Machine.
• Article on Ancient Egyptian lenses
• picture of the Ninive rock crystal lens^{[pranala mati permanèn]}
• Do Sensors “Outresolve” Lenses? Archived 2008-07-01 at the Wayback Machine.; on lens and sensor resolution interaction.