Nikon SB 20 - Manual (Page 51)

Ready-Light Warning Functions
To prevent errors, the ready-light inside the camera’s
viewfinder blinks in the cases listed below. When blink­
ing occurs, check the SB-20’s flash mode selector
setting, the camera’s shutter speed/mode selector set­
ting or film speed setting and adjust as necessary.
1) When SB-20 is set at TTL with cameras other than
Nikon F-501/N2020, F-401/N4004, F-301/N2000,
FA, FE2, or FG. Reset SB-20’s flash mode selector
to A or M.
2) When using the FA, FE2, or FG to perform TTL auto­
matic flash photography with the camera’s shutter
speed dial set at a mechanical setting (M250, M90
or B). Reset shutter speed dial to another shutter
speed setting. For M250, MOO or B setting, reset
SB-20's flash mode selector to A or M.
3) When performing programmed TTL auto or TTL
auto flash operation with a camera film speed set­
ting beyond the usable range. Use film within the
appropriate range for TTL auto flash photography
(ISO 25 to 400 with the F-401/N4004, FA, FE2 or
FG; ISO 25 to 1000 with the F-501/N2020 or F-301/
N2000). With the FA, ready-light also blinks when
the film speed setting on the oamera is near ISO 12.