Nikon Camera F3AF - Manual (Page 37)

FOCUS —continued
Special Situations
The F3AF provides autofocus and focus-aid operation in the
majority of cases, inciuding such difficult situations as fast-
moving sports events, subjects seen through glass, or scenes
containing point light sources, such as the flame from a candle
or a streetlight at night. However, if the overall subject is dark in
tone (e.g. when the illumination level is less than EV 4 at ASA/
ISO too), low in contrast, or lacks a distinct vertical line, the
focus-impossible warning blinks or glows continuously to inform
you that the camera’s TTL image displacement detecting sys­
tem will not work. In this case, you can set the lens' A-M switch
® to M and focus on the main subject manually using the matte
portion of the focusing screen. As an alternative, perform auto­
focus or focus-aid operation using another subject, if available,
which is located at the same distance as the one you want to
photograph; then, with the focus lock button depressed on
autofocus or without changing the distance setting in focus-aid
operation, point the camera at the original subject and take
the picture.
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