▁other ▁optical ▁device , ▁such ▁as ▁a ▁close - up ▁l ens , ▁tele con verter , ▁or ▁teles ide ▁converter , ▁the ▁camera ▁l ens ▁itself ▁is ▁properly ▁called ▁the ▁prime ▁l ens . ▁ ▁Prime ▁is ▁here ▁used ▁in ▁the ▁sense ▁of ▁primary , ▁chief , ▁original , ▁first ▁in ▁order , ▁etc . ▁ ▁L ens ▁manufact ur ers ▁such ▁as ▁AR RI ▁Media , ▁IS CO ▁P rec ision ▁Opt ics , ▁Schne ider , ▁Carl ▁Ze iss ▁AG , ▁Can on ▁and ▁others ▁still ▁make ▁variable ▁foc al ▁length ▁c ine ▁and ▁video ▁l enses ▁regularly ▁catalog ued ▁as ▁variable ▁prime ▁l enses . ▁ ▁A ▁variable ▁prime ▁is ▁sometimes ▁distinguished ▁from ▁a ▁" true ▁zoom " ▁in ▁that ▁the ▁latter ▁maintain s ▁focus ▁as ▁the ▁foc al ▁length ▁is ▁varied . ▁ ▁This ▁use ▁of ▁the ▁term ▁" prime ▁l ens " ▁is ▁an ▁example ▁of ▁a ▁retr onym . ▁ ▁Early ▁in ▁phot ography ▁only ▁primary ▁camera ▁l enses ▁were ▁available , ▁and ▁were ▁merely ▁called ▁" l enses " ▁or ▁" object ives ". ▁ ▁Later , ▁" aux ili ary " ▁l enses ▁were ▁available , ▁which ▁usually ▁fit ▁in ▁front ▁of ▁the ▁front ▁element ▁of ▁the ▁primary , ▁or ▁" prime " ▁l ens . ▁ ▁Popular ▁foc al ▁lengths ▁▁ ▁Many ▁l ens ▁manufact ur ers ▁produce ▁or ▁produced ▁prime ▁l enses ▁at ▁or ▁near ▁the ▁following ▁foc al ▁lengths : ▁ 2 0 mm , ▁ 2 4 mm , ▁