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In!that!context,!seekin g !the!id ea l!le ns !fo r!a!give n!sh oo ting !ap plica tion !must!envisage!broadening!
flexibilities!in!optical!and!system!developments!according!to!the!following:!
1. Highe r! Optical! Performance! —! to! a cco m m o da te! multiple! future! e nh an ce m en ts! in! cam e ra!
performance!
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2. !Increa se d !optical!speed!—!for!specific!lense s!
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3. Enhanced! Operational! Specifications! —!!such ! as! focal! lengt h! ran ge s,! maximum!aperture,! and!
their!controls!
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4. Meeting! demands! in! Size! and! Weight! Specifications! —! which! can ! be! critically! impo rt an t ! to!
certain!forms!of!shooting!
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The! ideal! lens! for! a! g iven ! shooting! application ! typically! se ek s! optimizatio n! of! on e! of! the ! three!
specifications,! generally! accompanied! by! a ! desire! to! also! e levate! the! priority! of! a! second! of! these!
specifications!—!as!suggested!in!Figure!5.!!!!Note!that!the!area!of!the!triangle!remains!cons ta nt !—!but!
the!increased!numb er!of!design!parame ters!offers!new!flexibilities!to!achieve!these!higher!design!goals.!!!
For! other! lens! designs,! there! are! also! more! options! available! to! support! a! more! favorable! balance!
between!the!three!specifications.!
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Figure&5&& Illustrating$the$d iversity$in$lens$designs$required$to$meet$con tem p ora ry$im a gin g$n eed s$
Over!the!decades!the!Canon!EOS!EF!lens!designs!have!supported!reasonable!flexibility!in!m a na g ing !o ft en !
conflicting!requ irem e nts!—!primarily! b ec au se!of!the!large!54! m m !mount.! !On!th e !other!h a n d,!the!lo ng e r!
44mm!flange!back!distance!(d istan ce!from!a!reference!p oin t! o n!the!lens! mount!to! th e!image!se ns or!)has!
hampered!certain!d egrees!of!freedom!in! some! lens!designs.!!That!space! between!the!final!lens!element!
and! the! im ag e ! sensor! (especially ! in! the ! case! o f! the! large! fu ll! frame! image! sensor)! is! inva lu a ble ! to!
achieving! optimization! of! the! projected! image! performance.!!Accordingly,! central! to! achieving!
extensions!in!lens!design!options!is!a!radical!red e sig n !o f!th e !len s !mount.!
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