How were Kubrick and cinematographer John Alcott able to film
scenes using only candles for lighting?
Kubrick obtained a special 50mm camera lens designed by the Zeiss
Corporation for use by NASA in shooting still pictures in the low
light levels of outer space. The lens was 2 f stops faster than
the fastest movie camera lens made at the time.
Kubrick had Cinema Products Corporation adapt a standard 35mm Mitchell
BNC movie camera so that the camera could accept the lens. Cinema
Products was later able to create two more special lenses by using
70mm projection lenses together with the 0.7 Zeiss 50mm lens.
These special lenses allowed Kubrick and Alcott to shoot the indoor
scenes using nothing but candlelight. This actually proved to be
very challenging, as the low light levels reduced the depth of field
and made it impossible to focus the cameras by eye.
Shields had to be installed above the sets (which were filmed in
actual castles in Ireland and England) to keep the heat and smoke
from the candles from damaging the ceilings. The candles also had
to constantly be replaced, to keep continuity during the scenes.