1939 B. Dudley in K. Henney & B. Dudley Handbk. Photogr. ix. 281 Spotlights... Med. screw or Med. prefocus.

1950 A. P. Young & L. Griffiths Automobile Electr. Equipm. (ed. 4) vi. 181 The bulb is of the pre-focus type now prevalent in British-made headlamps.

1967 L. Holmes Odhams New Motor Man. x. 238/1 For Continental towing, British cars must have their headlamps converted to dip to the right instead of to the left, and for this purpose special pre-focus bulbs can be obtained.

1972 Gloss. Electrotechnical, Power Terms (B.S.I.) iv. iii. 17 Prefocus cap, cap..which enables the luminous element to be brought into a specified position relative to the cap during the manufacture of the lamp.

1992 Mech. Products & Tools July 1481/3 The shank tip is fitted with a..pre-focus lamp and a threaded boss.

1951 Philips Techn. Rev. 12 312 (caption) On the base can be seen two of the three studs with which the lamp is focused: they ensure that the axis of the lamp coincides with that of the reflector, the filament being ‘prefocused’ with respect to the studs.

1963 D. Rethlingshafer Motivation as Related to Personality xi. 255 Organisms may be prefocused for oncoming stimuli.

1991 Photo Answers May 28/1 He's prefocused the scene perfectly, so that he knew he could safely click the shutter a fraction before the bike moved into the right position.

1996 Q. Jrnl. Royal Astron. Soc. 37 760 Stamm's preparation was the most extensive of all attempts that I know of—with him pre-focusing the telescope the night before.

2004 N.Y. Times (National ed.) 17 June e1/1 Most [workarounds] involve eliminating the focus lag, either by using manual focus or by prefocusing (half-pressing the shutter button).