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Various focusing aids can be iAcapntttoj in the viewing Bcittlli usually a split-image device is sei in the center of the field.. A Straight line ill the subiect passing thruugh this a tea will appear broken or split lE the lens is not focused on it, and the tine becomes Sre Dicucn 2-P continuous when the focus is coned,** iJ-MLcroprismsjr are another com nidi] aid: these exaggerate the vi&ual effect of sllgElt focusing errors to help the photographer see clearly when he has achieved correct focus. Other Ticwflnd« scnccns jre intcndcrt for special a pp] Lea (ions, such Afl fl teotangutargriJ pattern Useful V i.th a rchilec-Luraf or other rectElinear subiects, or screens for pbutomacrography. In sume tases a change of screen may be required when using very long lensft.
The great popularity of smgle-lens reflex design ls due to the-fact that the photographer sees the precise composition nf the image, regardless ol die focal length of the lens, or the use of polariEcrs, Close-up systems, or other attacliments. Fur this reason, single-lens reilex cameras can be used with zijom Lenses, telescopes, micro scopes, and other oplical iystema.
The drawbacks oJ thLs design are comparatively minor, and relate to the presence of the mLrror in the viewing system. The need for a minor adds mechanical complexly, vibntion, and noise, and causes the black-out oi the viewing image already mentioned.
In recent years, increasing emphasis has E»een placed on compactness ot camera design. Since smaller size is usually achieved ai the eitpCrtie of operational k-JtuK's. the photographer usually jiiusI choose, actnrdtng tn peTKinal preference, the besL balancc between compactness and light weight, and camera capabilities. The t'ccl
] Ji Amall-Fn rmai Camera s uf j carat:ra in the hand ¿ltd (lie accessibility of controls must be taken into account.
Currcn cameras arc aba designed as modular "'systems,'' often WLth a great number of Uireichflngeible eompnncnL-s. The photographer who intends to add to lus equipment gradually UlUSC be especially caicful in Ills initial choice of camera liner viewing lllfl decision Ji the tiiSt Step id 4 jong-teim acqLsisition. In addition tu lenses, ihe camera system is lively to include ¡1 variety of viewing screens and prions, bellows, and, frequently, mutor drives. The motor drive pctinirs rapid sequences of exposures, up Tf> five frames per second, or simpfy advances the film rapidly after each exposure. Smaller vei^mn-. nf the motor drive called auto-winders, permit eipusurtt at about two lianu» per SOCOnd, pr autnmacie film advance for individual txpcfitJrti. Some cameras can be fined with large magazines hnldinp hundreds nf exposures, a useful fi.eeftSSOJry WLth the mutOf drive.
Although they must he judiciously employed for optimum Jesuits, the AUiomiclc CXpDSute sj/itecui tliat are increasingly a part nf Camera design do offer advantages in situ aliens wltcic quick camera operacinn is important Mqm. such exposure systems measure the Li&hc uaiismitted by the lens itself, so they always read all or a Specified part of the aiea cn-vcicd lny the lens in use.
The terms averting, center weighted, and spot leading are used in describe the rfituie uf the upuute reading. As its name implies, ■in ave[aging, iystttn reads the entire intake uci and averages the values. A center-weighted system makes the exposuie determination primarily «^qnrdine to the light values in the central portion uf the pit tun; area, with lessor influenLC by peripheral areas. The assumption is thai the most important subject areas are usually tn the central portion uf tlie view Under |a questlonible assumption frum my puint of view I. A spot-reading system measures only a small central portion of the image area, usually indicated as a small circleoji the focusing screen,
With a b-s-sii; raectnng system, the photographer adiLists shudcr speed and aperture unEil a ttccdJc ot array nf lights ILF-D's) ill the
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viewHndet indit-Htes cunect dpdiHUi}, An automated camera will set one uf thcic functiciii unassisted once the photographer has pee set the udier. The« systems are designated "shutter speed priority'' ui "aperrure priority" to indicate which control the pho-tugiaphci adjusts, and diertarc ifgum-entl in Livor nf each approach. WLtLi shutter speed piinrity, which sonic pliningiapheis find more convenient., the (anicrii automatically sets (tw diaphragm loeated an the lens assembly? thus only lenses that at* specifically matched to 11i4i citnf.ia's automatic tuimols an be used With aperture priority, a Wtder election ot lenses rs usually available, tince the autum.ition uf the sbutm remains inmct despite lent changes.
[n either ease die phmogiaphcr must monEtoi the indicated set-dng thai wilE he made by the camera to be sure it ls appropriate tor his subject. Impending on the aperture L'hnseii, for example, the expnsuic system may choosc a shutter spceJ (Jut js too slow for a mewving fiihicctr l heri is almost always an Indicator to ¿how the ^proskmate value uf the automated setting, and die photographer Mi diLS case mUH ehi»K4 laiger aperture to peimir a shorter exposure tune. A few cameras have-a "program" that allows the camera to set botii the apeirure and shutter speed, and some cameras give the phuiogiaphei a choice of several metering mode*.
1 want In emphasize that excessive icliante on automation can lead to intnrrcct exposures as well as ccurect ones, Conditions such as strong hack- nr side-lighting, nr contrast diat diIters from "average/1 can mislead iinynfthg «cposure system* described. Mngt canu-ras permit manually increasing or decie&sing the exposure ovei a tciral ra^igt; of two ^ fo l> r (-stops, and 1 strongly recommend dun vou a^oid any came» without such a pronoun, f onee experimented with a very fine cutneia uf leading make that bad a built-in spot reading eiposuie system uf irmaikable accuiacy—1 chetked it carefully With a flue photometer. Nowheic in ihe insirueuons. however. was it explained that leading a dark or li^ht area of the subject widiin die central-spot area could pr-nduce incnncct overall cxpn-suic [crposurc dctcrniinatinn will he fully discussed in Bnok 2 of this sericsl- The fact that esscniial information needed to use the automatic exposure system Intelligently wai nat pictured in the instructions ledy 1 am sure, to many poareKpMae* In spite of the very high quality of tbc exposure system itself. Unfortunately, many current instruction manuals are equally unclear. However sophisticated and accurate they may be, autmnatcd cameras cannot replace creative sensibility and undemanding in photography,
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