Nyob hauv nws cov ntsiab lus yooj yim tshaj plaws, focal ntev yog qhov pom ntawm lub koob yees duab lens.
Focal ntev txiav txim siab npaum li cas ntawm qhov xwm txheej uas lub koob yees duab pom, thiab nws txawv nrog lub lens. Lub kaum sab xis dav tuaj yeem coj mus rau tag nrho toj roob hauv pes; telephoto lens zoom rau ntawm qhov chaw me me nyob deb.
Focal ntev yog qhov tseem ceeb kom nkag siab, tshwj xeeb yog tias koj tab tom tua nrog lub koob yees duab DSLR. Qee qhov kev paub yooj yim ntawm lub tswv yim tuaj yeem pab koj xaiv lub lens zoo rau ib qho kev kawm thiab paub tias yuav xav li cas txawm tias ua ntej koj saib los ntawm viewfinder.
Technical txhais ntawm Focal Length
Lub ntsiab lus tshawb fawb ntawm focal ntev mus zoo li no: Thaum cov kab hluav taws xob sib luag ntawm lub teeb tsoo lub lens tsom ntawm infinity, lawv sib sau ua ib qho chaw focal. Lub focal ntev ntawm lub lens yog qhov kev ncua deb ntawm nruab nrab ntawm lub lens mus rau qhov focal point.
Lwm txoj hauv kev kom nkag siab qhov ntev focal tsuas yog qhov kev ncua deb ntawm qhov nruab nrab ntawm koj lub lens mus rau cov ntsiab lus nws tau tsom mus rau.
Lub focal ntev ntawm lub lens yog tso tawm ntawm lub thoob ntawm lub lens.
Type of Lenses
Lens feem ntau yog categorized li wide-angle, standard (los yog ib txwm), los yog telephoto. Lub focal ntev ntawm lub lens txiav txim lub kaum sab xis ntawm qhov pom, yog li lub lens dav dav muaj qhov ntev me me, thiab lub lens telephoto muaj qhov loj focal ntev.
Ntawm no yog qhov lees paub qhov ntev focal ntev rau txhua qeb ntawm lub lens:
- Tsawg dua 21mm: Super wide-angle lens
- 21-35mm: Wide-angle lens
- 35-70mm: Standard / Normal lens
- 70-135mm: Standard Telephoto
- 135-300mm (los yog ntau dua): Telephoto
Zoom and Prime Lenses
Muaj ob hom lo ntsiab muag: prime (los yog tsau) thiab zoom.
- Ib lub lens tseem ceeb tsuas muaj ib qhov ntev focal (piv txwv li, 50mm).
- Ib lub lens zoom npog ntau qhov focal lengths (piv txwv li, 17-40mm).
Zoom Lens Advantages
Zoom lo ntsiab muag cia koj hloov lub focal lengths sai sai thaum saib los ntawm viewfinder, yog li koj tsis tas yuav nqa lub hnab ntim lub koob yees duab puv lo ntsiab muag ncig. Feem ntau cov kws yees duab amateur digital tuaj yeem tau txais los ntawm ib lossis ob lub zoom lo ntsiab muag uas npog tag nrho ntawm cov focal lengths.
Ib yam yuav tsum xav txog yog qhov loj npaum li cas ntawm qhov koj xav tau hauv ib lub lens zoom. Ntau lo ntsiab muag mus los ntawm 24mm mus rau 300mm (thiab nyob qhov twg hauv nruab nrab), thiab cov no yooj yim heev.
Qhov teeb meem feem ntau yog qhov zoo ntawm cov iav hauv cov lo ntsiab muag; Qhov ntawd yog vim hais tias, qhov dav dav, qhov ntau lub teeb yuav tsum tau taug kev. Yog tias koj txaus siab rau ib qho ntawm cov dynamic-ntau lo ntsiab muag thiab xav tau cov duab zoo tshaj plaws, nws yuav yog qhov zoo tshaj plaws rau splurge ntawm lub lens zoo tshaj plaws.
Prime Lens Advantages
Prime lo ntsiab muag muaj ob lub ntsiab zoo: zoo thiab ceev.
Speed hais txog qhov dav tshaj plaws aperture (f/stop) ua rau hauv lub lens. Ntawm qhov qis aperture (tus lej me, qhib dav), koj tuaj yeem thaij duab hauv lub teeb qis thiab siv lub shutter ceev ceev uas yuav tsum tsis txhob ua. Qhov no yog vim li cas f / 1.8 yog qhov nyiam aperture hauv lo ntsiab muag. Zoom lo ntsiab muag tsis tshua muaj qhov ceev no, thiab yog tias lawv ua, lawv kim heev.
Lub lens tseem ceeb kuj yog qhov yooj yim dua hauv kev tsim kho dua li lub lens zoom vim tias cov iav tsawg dua nyob rau hauv lub thoob, thiab nws tsis tas yuav txav mus los kho qhov ntev focal. Tsawg iav mus los ntawm txhais tau tias tsis muaj caij nyoog rau distortion; qhov no feem ntau yields ntau sharper, clearer duab.
Focal Length Magnifier
Lub focal ntev ntawm lo ntsiab muag tau teeb tsa rov qab rau hnub ntawm kev yees duab yees duab thiab cuam tshuam rau qhov ntev ntawm lub lens ntawm lub koob yees duab 35mm.
Hauv kev yees duab, 35mm yog hais txog hom zaj duab xis siv, tsis yog qhov ntev focal.
Yog tias koj muaj hmoo txaus los muaj tus kws tshaj lij DSLR, ces koj qhov ntev focal tsis cuam tshuam. Txawm li cas los xij, yog tias koj siv lub koob yees duab qoob loo (APS-C), ces koj qhov focal lengths yuav raug cuam tshuam. Vim hais tias qoob loo-thav duab sensors me dua 35mm strip ntawm zaj duab xis, magnification yuav tsum tau siv. Lub magnification txawv me ntsis ntawm cov tuam txhab, tab sis tus qauv yog x1.6. Canon siv qhov kev nthuav dav no, tab sis Nikon siv x1.5 thiab Olympus siv x2.
Piv txwv li, ntawm Canon qoob loo-thav duab lub koob yees duab, tus qauv 50mm lens dhau los ua tus qauv telephoto 80mm lens (50mm multiplied by a factor of 1.6, to result in 80mm).
Ntau cov tuam txhab tam sim no tsim cov lo ntsiab muag uas tso cai rau qhov kev nthuav dav no, thiab lawv tsuas yog ua haujlwm ntawm cov koob yees duab qoob loo. Qhov no yog qhov tshwj xeeb tshaj yog muaj txiaj ntsig ntawm qhov dav ntawm qhov kawg ntawm cov khoom, qhov kev nthuav dav tuaj yeem hloov cov lo ntsiab muag rau hauv cov qauv!
