Nikon Camera N90 - Manual (Page 229)

Release-Priority for autofocus
Shutter can be released anytime (i.e,, even when subject is not
in focus). Convenient so you do not miss an opportunity to take
a picture and are not concerned with absolute focusing
precision.
With N90 camera body, Release-Priority is given to Continuous
Servo AF while Focus-Priority is given to Single Servo AF.
Flowever, the Electronic Organizer can change the priority to
perform Focus-Priority Continuous Servo AF or Release-Priority
Single Servo AF.
Single Servo AF
Once the subject is in focus, focus is locked. Useful for
recomposing the picture.
SLR
Single Lens Reflex. A type of camera in which you look through
the camera's lens as you view through the cameras viewfinder.
Other camera functions, such as light metering and flash
control, also operate through the camera’s lens.
TTL
Through-the-Lens. Most SLR cameras have built-in meters
which measure light after it has passed through the lens, a
feature that enables exposure readings to be taken from the
actual image about to be recorded on film, whatever the lens
angle of view and regardless of whether a filter is used or not.
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