Exposure Intensity X Tim or E It

In this fnrmula, intensity refers in the light that teaches the flltft, not îu^t the suhiccc luminances, and there lore depends partly on the npcTturc setting. Relating the subjett luminances widi the film's sensitivity, and indicating the aperrute an J shutlci speed that will provide optimum exposure is die Function ni the exposure tneLer I with Qn additional large m-easute ot human judgm e ni r see IJook 1) Once the desired exposure is knnwn, the formula above shows tliut, it the mrensLty :s reduced, the time muse Ex increased cu uh I .Li n die >ame Lutal exposure. To facilitate such adjustments the modern seek?- ill shutter speed setting are in geometric progression, related by a 1:2 ratio, so that each sbutter speed is olle Eiall at twice lilt id|acent valuA! une second, lfl. 1 a i 0, 1/15, 1/30, 1/SQ, and so on, The minded wluiis—i/15 instead of 1/L6, Uffl instead n( l/fi4—are well within acceptable tolerance limits.*

Since Lii i s 1 :2 ivl.ii ioili.llEp exius with bot h the sh utter speeds and chc apertures, thereat- always i number ni Jj lièrent I-stop-shutter-speed combinations that will give the same LOEal exposure to the film, for example, if an exposure ol 1/1 second at f/12 is currect, llien any of thçse nrher enmhinatinns would also be correct: 1/4 second at f/lS, l/A at f/11 1/15 at i/flF 1/30 at i/5-6, and sn un. In each use the shutter speed is one hall the pteviuus value, but the apenure ii upened une siup to admit twice a.4 much light

Most shutters have une ur two additional setting1: for long tiX-pOSUtis; H standi Lor hulbr which keeps (he shutter open for as long ■ iï the shutter release is dëprtsaed, and f for time, which tipetii the slid I ter lite flm tune the rdeaSB l:- pressed and closer it the second nnKrot through a separate action suth as turning the -butter speed dlil. "i inc n 'tniug is umiiilb convenient for acponuna of one-hidE to several seconds, and T Is useful for very long exposures. On cumeras thai hive only the B setting; ike use of a locking cable

"TTi ■■ □ccrptid eflifj [hinil-r ¿peed n^qmih wnt |, i / J. I.-, I --" 111. I/,1"'. t/K,

Li J00, T/JfiÛ—haiJLy a c.Munccn: ji:<iE[Ewi:inl

Shatters SI

|AI An □ thuiEEd ;h=L-J i:-l Li'i';l ■imij, ui: " jl;[ lb "draced," . nd ll- ■ i [¡i, '. .l-pi'lmiicl

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[CI A '. '. Illjli'.'in jll! of J KCDDfl ill i 111.' uioi■ iikii : uiih- wucr Id iii' i cTeulf I'jv: il-jil hy :ln; ujlli ■li :Ll joucilLjrii,.. A suae air •m.1, h_:h ji j jutk, eiubilibti ■ i-r-lu mi rclcticic.

release will helji in mating vity long exposures A stopwatch w]JI permit acruratclv rimed exposures

Given a range ot ami sliuirei ftfrfei-i com hina Lions iti^i pio vide equivalent Qprnifl^ the plwtqgT*phcT must consider his creative purpose and die conditions lIijl prcvaiE when deciding whith combination ta Use Ii movement of either the Hubjcct dj camera is anticipated. a fast shutter -pee J will be require J to prevent blur reef movement ot the subjetton the film/- The use of long Lenses with

held cimerji .il-:i die tares very iasE shutttt speed*, sinrt slight tremors of ihe camera will pioducc .1 noticcable Lliss at image sharp DHI Ol even a blurred image, On the other hand, if the UDCm lS mounted on a tripod and the subject is stationary,, very long exposures become practical. The phutugrapher should he aware, hc^v-CVUt, thai exposures longer than about one second may resume OflfrtCttCh J(u the reciprocity eiJeut «

The choice of shutter ¡¡peed must alio be made With consideration for the aperture that will apply. .IS fasHIr shutter S[:ied- Will requilL- (he UK of lurgcr apCtmres, with resulting fuiS of depth of field. Them ;ire many ocuakmx when wt must compromise between Lhe demandn for short exposure timet and depth of field. Tti situations where these two requirements arise frequently, s»eh as photographing news ot sprigs events, photq0Hpb«t^ prefer * highspeed film. Sncii flEms. heenuse f<i their gre.iier scniltiviry to light, permit bath East shutter speeds and small hi moderate apcrLunes when used under normal daytime lighting. Unfnnunaiely ii-.inj3 high-speed film involves some sacrifice of image quality compared with slower films |fi!m speed and related issues ui discussed fully ml Cook 2; L will make tome rcccunmenda Lions regarding choice of shottcT speed in Chapter S|. Note thai terms relating to ''speed" are used In several senses in photography, and they should nnt be

.43 ."ih L±t ic-rs cf.nl used. Both filrv.M and dnttEn have speeds, die former expressed ■s an index numbci on the ASA or other stale, and the latter ¿r fractions uf a second. Lenses, tdu, are described as tast ei slow copending on their laigest relative apertuie.

SHUTTER TYPES

Leaf Shutters

The leaf shurter consist (if a series nl hlades Lhai, when lTi£ shatter ls closed, iiverlap to keep r:ui lighrr a rotating ring upens and clow the blades during cxposum. The Leaf shuiter Ls located within the tens neat the diaphragm.

A Timing mecheoLsm controls tbe opening and closing at tine blades In <-Omt: earlier ¡-buttcri, the riming was controlled hv an air piston and cylinder} and tbis system often proved ejttrcmeLy hdlnbk. I have an eatly vumpur shutter of this type Ln a latjj;

c

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Tilt hltdo npoti iiiii. i Ink cjc

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71- h jI■ pi iip-- fu.i:.iin .¡I th^ !.i'i| i wivn ¡r'im riphi hn Mt i ■ ■ ruTclLTiB iccv fait ji ■ u tbi lil-.i. jvroduci* .'.ii ei-r-i-'Jii nE IfWO Ktond il' l^iit wider L'jrrjLn thi cn-h-p il V HKspMUKoC l^M ho: nd Tr.t ■■ ji!"i of nil nptnmi; ii..m* lujihifi :il t n-irlriLj i!I I 1el' . _ At ei-puma of LiH) mJ -i L-.'im-i, ilii l!i-.:-LiruiJi IIIIIv <i kpiH the !i! i hrbira il-. IfiflMld fceiifll ¿rti'ivtrtu «O lfiriiljiiiL<

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TVi-d i'ii:u:i ■ "m m.iUL wiib in ■ ■"■nil- Il i ll -"-I ilrnuT I U>nmnd duuciDD.

Sheers S3

PruMr lens, and after forty years it Mill pirftnTOi with Riaiifying utuae^

Most shutters tnJuy use a meehunit31 i;ear train, similar (li a ■v jllLj mechanism, to control timing, ui this (uncthHl iv performed electronically. The new electronic shutter? Etttjodut-ed in the l?7Q5 arc marvel ^ of design and accuracy. The practical upper J Lin it til posure limes with leal liLnrcts is not generally taster chan 1/500 second, MnCe I he shutier blades must complete acyeJe that involves nwvlllg LO Hie fully open pasttiOTI a ltd then revering direction tu close, A leaf shutter for view camera use Will also usually have a manual settLiig m open the shutter roi viewing. although with some the time or hulh settings are used, i Laving a sepurate control lever on the Lhuttcr is hesi, as it eliminates the need to reset the shutter speed between viewing and photographing, iiome cunenc electronic shutters have very precise Ions exposure times, up to about JO seconds. in addition to the standard inst speeds.

View camera leni are usually mounted in shutters, So that ihe entire CriScmiilL.- is icpUced when lenses are interchanged. A few shurteis, however, ¡u c mude ior use lie hind or m front of a vfcw-cauiem k-n\ -md t1l,Ui CS1i he Uicd wjiIl ,i variety of lenses, especially the process type, The current Packard shuLter, first introduced 11 l I 7, fu rictions a t time. hulb, n 11 lI relatively slow speeds, aod dtus can be used fur vtudio and field WOtfc when short expci-sure> are not required ¡about £ff percent of my View-camert exposures .ice second or kingec|. Smiir aln niiikes in excellent -■hutcer foe its new camera with a widec range of speeds

Foeal-Plane Shutter*

A focal-plane shutter, as ¡es name implies. Is mounted near the film p| ¡i oe tu the i f h rtn dt the lens fatly iocal-plane si itLitt-1 i were made

, ilJlie lipiDUd. IjlbL-.'rijjIL II LCUll'J

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Lii i ¡I. .* i■a_.11 I'IJLILJ cnrLjjn mmtt. A l*ii ■ li.iri'jr ■ r:l J iSf-'H "Ik -:1m ihmu|h j nmp^rw umain >'■■ in ihu nH fliir "f ih1' i"i mm- i'

««pilWll gt .1 JinlUlT JilltrriH mil riL nl 11: in tliL- irlldr

j-iuicL'i LjruLii rU'iiiJ i:i ihL nppo-- IL -f irL■ J1111ri >1 -L. in.ir/' cm llw nl m "!■■ Iiiwrr n^hi i-i-.in- is r^ -r .mi ' ¡4du^jlag lli-j - i u i il l'j . "_l I.ii ii j. i J I.il Ifii.id.i. SIlhLlI ill JILE I :iIL ibmpkm

£4 Shutters up of n euitils with sluts of fllffeMUt widths and. in some Ciscs, Adjustable tpTinjt teutons tu alter tlie speed at which the curtail-, traded. Que a! the slits passed ¿cross the him iuit<iee to mfllttttlE exposure, and different exposure times Weii SikcieJ by chaqpoj ihr widlhs and turtoun speed, Current ftnfil-pUne 1llcicyji unfllfy «insist of two w:p;ww curtains As the Ami one n.n/ck aemss \ne local plane it uticu^eo tlie film io begin ih-e exposure. and ihc second curtain follows after a controlled tmen>al to terminan

I lii." UJipoSUlC."^

At longer exposures the first curinln will open completely, and, ¡tsier i he measured dei.iy, the second curtain ihe» rinses. Ah da shutter speeds become faster, however, the second curtain hegjeu cLnsiiig helorc tht; lii-i lus I u 11 v uncovered <he film, thus fnllnwjiifi (he lit si curlaim aooss ihe film, Tbc eitpnsuic i- made through s3n lormcd by ihe lwo curtains, and very last .sltuirer times aTr pr«--,ihle. Many receni eann:ra> have shutters lite the C7op:i I -Square, using set» L'l metal blades li'i.-n overlap Lite j Venetian blind inLrej j i i a curtain. Since the curtains or metal blades fnr .Innini camera rraveL a.c a htgh t-ne and frnm a very narrnw slit, shutter speeds « 1 /IOC»second or fairer ate possihle.

One difficulty in designing focal-plane shutters is that became <if inertia. iltey tend to accelerate as they crnss lJic film pi .n. Modem local-p3ane shutters are corrected in ensure unitom: li

Shutters to

Shutters to

hpuid (i "jl.iii« Hfcnü Limrac. lun.1 rr."i ■ ' ii; .-Ii" im-hi.'r I ■ i : ur- ■!. 12 1 hl- iLHi;

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liiuCE nl lit i. 11■ iiimir, cd ..i ■ !n Elni i jii'j ij ul ii: r Lliu ijiprinpf iCjHJlLiV ]||!tin3lli iiijl Miur.iln 111 liMintiupliv H.Cf«lflt E-iiLiiiji.i üintl pu.!ur», hilt ic in wurth white tn cest by phntDgraphiiiE an evenly hghred suTiate exposed an ahout Zone VE |see Ekiok 2|. Variation vi cnrtain speed oi -ILi width [hat is nnt cnrrccted will shnw na a change in film density at GM «Jgjc af the negative, parallel tn ihc ed^c nf the (ihmter cürtiins. Thifl ungven density is eipecully appatent when plioco^irnrhLrsp a re h i teer u te, paJnrlUfS. OT niher üuh-feers with a continnu.i-v.dLLi; ;iiea .ictc^s tlie Ulm. in OtHnjlJcJt n^jccis, such m foliage, Lhe effect is Imrdly sten,

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