APO lens: What is it and how does it work?

An APO or apochromatic lens is usually an anonymous design feature. You may see APO on your lens. A fundamental problem with camera optics ... Skiptocontent» HomeTechnologyguides InthisarticlewelookattheAPOlens,providingaguidetowhatitisforandhowitworks Apochromaticlensesuseagroupofthreelenselementstoreducecolourfringing(asabove).Achromaticimageleft;Apochromaticimageright AnAPOorapochromaticlensis usuallyananonymousdesignfeature. YoumayseeAPOonyourlens. Afundamentalproblemwithcameraopticsisthatthelightthatformstheimageonthefilmorsensorcomprisesarangeofwavelengths.Uncorrected,usingasimplelensdesign,thesedifferentwavelengthsfocusatslightlydifferentdistancesrelativetothefilmorsensorplane.Thisresultsinsoftimagesandchromaticaberrationswheredetailsintheimagebreakupintorainbowcolours.Thisiscalledcolourfringing.LensdesignershavefoughttokeepthispropertyoflightundercontrolformanyyearsandanAPOlensis oneofthemoresophisticatedsolutions. Thesimplersolutionistocombinetwolenselementsintoagroupthataccuratelyfocusestwoprimarywavelengths,forexampleredandblue.Thisisanachromaticdesign.It’sinexpensive,simpleandbringstangiblebenefit,especiallyforblack&whitephotography.Butthejobisnotentirelydone,asathirdprimarycolourwavelength,green,forexample,willremainuncorrected.ThisiswheretheAPOlens comesinasanapochromaticlens,typicallyusingagroupofthreelenselements,eachhavingcarefullymatchedlowopticaldispersionpropertiestoaccuratelyfocusred,greenandbluelight. Achromaticlenseshavebeenaroundforover100years,butapochromaticlenseshaveonlybeenwidelyusedinmorerecentdecades.‘APO’markedonalens,intheory,identifiesitasanapochromaticdesign,butmanufacturershavealsousedthetermasamarketingtooltoidentifyalensasahigh-performer–evenifreviewssometimescontradictthisclaim,whileotherlensesnotclaimedtobe‘APO’cangarnerravereviews. Apochromaticdesignsareusuallyfoundinhigh-performancetelephotolensesand,unsurprisingly,intelescopes. Cameraselectortool Getcamerarecommendationstailoredtoyourneeds:useourCameraSelectortool ReviewFinder AllReviewCategories ArchiveCompactCameraReviewsCompactSystemCameraReviewsDigitalSLRReviewsEquipment&ReviewsLensReviewsProductReviews AllManufacturers AdobeCanonCasioFujifilmGeneralImagingKodakLaowaLeicaNikonNokiaOlympusPanasonicPentaxPolaroidRicohSamsungSamyangSanyoSigmaSonySonyEricssonTamronTokinaVariousVivitarZeiss AllReviewTypes FieldTest MinPrice £5 £10 £15 £20 £25 £30 £35 £40 £45 £50 £100 £200 £300 £400 £500 £600 £700 £800 £900 £1,000 £1,100 £1,200 £1,300 £1,400 £1,500 £1,600 £1,700 £1,800 £1,900 £2,000 to MaxPrice £5 £10 £15 £20 £25 £30 £35 £40 £45 £50 £100 £200 £300 £400 £500 £600 £700 £800 £900 £1,000 £1,100 £1,200 £1,300 £1,400 £1,500 £1,600 £1,700 £1,800 £1,900 £2,000 Populararticles Weroundupthebesttravelcompactcamerasforcurrentlyavailableonthemarket,coveringeverythingfrombudgettoughcamerastoadvancedcompacts Full-frameDSLRsoffertheverybestinimagequality,butwhichoneisbestsuitedtoyou?We'vepickaselectionofthebestfull-frame… TheBestBridgeCameraof2016-Weselectsomeofthebestbridgecamerascurrentlyonthemarket Welistsomeofthebestsmartphoneaccessoriesonthemarketrightnow. Gettingyourselfinamemorycardmuddleandnotsurewhichcardtobuy?Welookatmemorycardspeedsandthefastestmemorycard… Whicharethebestcompactcamerasonthemarketrightnow?Findoutinourselectionofthebestcompactcamerasof2016 Akitlensisagreatstartingpoint,butwhatshouldyoubelookingtobuynext?Welistsomeoftheoptionsforentry…