Lenws

IMAGF FORMATION AND FOCAL LFNfiTH

A lens has twn Important pmpcrtieH rat .nhaied hy che pinhri-Jc. ÏLrst, ir can gnther lighi ove: îi targc aiea [the íioin surfocc of the Jcns|t thus prodttcing an image hright enough iot ptactical photog' raphy. Second, eî fucus» the light lu produre a shaip image uf a subrccL plane. À plnEuile dncs not fncu* the liRht; and lias no defi-5« n^-i uLeg f(içal J«vgçh,i3

Thd focusing ti light rayauccurs bccause h¿ht pnssmg frum ene mi-JniNL [Such Us air| intu anuïher Iglasil, ni Eium cae glass type r.u ntthei, changes sptcd ai the interface where thé twn mect. M the -uilacc Lh at an angle to ihe pach ni light, ihc Jighl ray wtlL changc direction, The change oE direction, Jinown as re/ïflCU'OJT, £aii be uoiltrulkd L■ ■. Vâiying tile slupe and cum position r-t the gEasi s» Tianirp 5-1 |ur pla sticl ekmrnts Lif a lrns.^1

One of the mnst Important characicriitiçs nf a Iciiy is ¡1g facal iengifi Tçehnicalïy, ïhis refere die disuocc ítom ihe reu/ nndiil ppiÜt of ihe Lena jusually dasi tn lite apüítLUc plane! lu the pEanc Where subjects ut Infiniry tûme intu Eucua.^ Knnwing the incal kngth lk utLportant not onjy hecause it identifies the distance of the km frnm [ht film (for distant jubj^rsl, but becaUK if JïfOYJiks â mensure of the image size atid sobjeet iïea in relation tu the film formar. TE y ou ust n short iucal kngth kits tu photugraph a suhiect, yen! will obtain an image uf a gjeater atea uf the subfect^ and caeh pan uf the subjcct wi]l he ümalkr in the ptiotograph, llvtu tí yoti UH îi longer lem. When \ htsi became a va te uf the [eut and the image it fuiras in relation to die subjeet, J chuught uf the kns as "tmhraclnp" the miter wntld.

í:í jil ] -l. ímj^r iijrm jliijD 1 ■ u j/mnlt; lenf LIRKL ¿rnic J Mjb|fcc

'Illds:-! ¡I l'^I.^H pl n fjDtk pnmr tvhinJ ITir Iriu, |ni| iHl- n-ni irni.e,': ji -lie kcumuidnctn :>f ail iucK pcanii. I!1- Lorni^niu ibli iLlmuitliin fckli n^ure 1-1, du

■ 'Il .'■ I ml iifL.jILM 1 piILhúJb VVLÜÜ * itrtl L J II hc LLll T.IL lbfli "Kfllînn" li^hh inrr it^ Cn1:rr 'ih-ficr. pendue in^ j murh britlrrr unjRr. jnd n JncuKi îhr lighl [□ rioducc j h j r | ;-j r iioijt^ iban lIk pLnhnli.

Pittair 5 ^ r-"■ ■ i■ iii-iii" JfiiBr'i Licht rrorn ^ nh lie: point Ji irlinrv prn-iIikd i'..i i:IlI i which jn n'JiKCLd ! ■ i lie lull h- eiiliie ji i.

.ii|;Il- |!' im. tll± iIi.Ijjili iihm iliv llita Lu I ho. fulllL li lilt din:aI

lentil ill Hif Inn

5tt bi^re i-ll

(iirr i J. ComjftHUt Inn- A Icrtj aFanc :Lcmcni ¡a ■ ■.raplc" 1cm LBTINLIII: litipdiicLiLuii- :HJM.V

.J tali.ii h nit be rtrmHtf nr HHttallnd In1 minf i mimhi uf Irui i-'m n-' Tlf reir i:-'.lul pljnL ulib: cnmpDL.nil leru u ihc inui

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JDLiI leftjfiJl roll.f bt luttltj » ppriua blttaalitll form Thr Itni ■pcTtnn li uv=lEIt pcndDDrd dun ■ii cSk n-.'!jl |iIjIlj.

k is impnnaiu to undcthj nrf that flJJ lensef of the.' idlilr f0C(jJ length give images o/ the «me s/zr for a given subject and uihject ^Mintt. li a 4-aneh Lens pndutei ,m Im^p one loch hijih of a OcrLam subnet, the image sue will remam one inch regardless OF whether rhe lens is on a ¿kSmm camera nr a -fio camera. However, on the 3 "mm camera, the onc-inch ima^e will till the frame | a bout [x I Vz inches), while it will occupy only about one quartcs the height of the 4i5 film ^Tbus thiiiubjett will he isolaied on .iSram film, vrhdJe it will appear In the midst of its surroundings in the 4x5 format.

We should also understand that tmu^ ii=Ll is pnj(mri/i?rriiJ rt? (actf! Ji;n^fh. [J. while making a phntngraph, ynu change to a lens nf don hie the ideal Ifiigrll oi the llrsr, each object wiEl doubie in sine in the image. Ai the «me tine rhe total wklih bi subject area covered by the longer lens will be hall thai of the shorter lira, Tints when you change from a 6-inch lens to a 13-inch len^ with a 4sS camera, ot from a .iClmm lens to a HOIImm Lens with a -33mm

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