User Guide

tical path
The light rays of an image come through the
camera 's tak i ng lens, and part of the light passes
through the main mirror's semi-transparent area .
The sub-mirror behind the main mirror deflects the
optical path downward , so the light reaches the
N4004's autofocus sensor module AM200 .
The AM200 autofocus system consists of two
parts: the optical block and the CCO package.
AM200 autofocus sensor module
The light rays coming through the camera's taking
lens enter the AM200 through a filter which stops
infrared rays from entry .
They converge toward the focal point around the
filter, which is the geometric equivalent of the film
plane . From this focal point the light rays diverge ,
coming into contact with the single-component op-
tical block . The block 's top spherical surface serves
as the field condenser lens . (The one - block trans -
parent plastic design enhances imaging stability .)
The divergent light rays are then reflected at the
slanted surface ; they then go horizontally toward
Len s
AF Nikkor lens
N4004 camera body
Electronic
co ntact s
the two spherical surfaces A and B at the end of
the opt i cal block .
These spherical surfaces serve as the separator
lens , from which the light rays converge toward the
line sensor package . There , they reach the CCO line
sensors.
Surface A makes the light converge at the upper
CCO line sensor and surface B makes the light
converge at the lower CCO line sensor.
Through this process , the image as seen in the
focusing frame marks of the viewfinder is duplical:
ed and each of the two images is projected onto
each line CCO sensor.
AF line sensor package
This package consists of autofocus sensors in-
corporating a pair of CCO line sensors with 100
elements each. All in all, 200 CCO elements are
used , the largest number among SLR cameras . The
more CCO elements there are , the more information
can be collated ; focus detection becomes more
precise because judgment is based on the amount
of information .
Seq u ence
motor
DECISION MASTER SYSTEM
Phase detection autofocus system
The CCO sensors generate an electric output in
accordance with the brightness of the image . The
computer analyzes the output from the CCOs and
determines the amount of defocus to control lens
movement through the AF mechanism .
Electronically controlled AF motor
The computer monitors the AF motor electronically .
The digital encoder outputs 14 .5 pulse signals per
revolution of the motor. The calculated defocus
amount is then compared to this signal by the com -
puter. Motor movement is controlled with a 5- step
driving force that accurately moves the lens
towards and stops it at the exact in-focus pOint.
Improved total optical performance
The autofocus sensor of an autofocus SLR camera
requires as much li ght as poss i ble. The more li ght
there is that comes through the camera tak i ng lens,
the easier it is to increase autofocus detection
capability . But there are other factors such as the
light that reaches the exposure metering sensor
and the light that reaches the viewfinder eyepiece .
To meet the need for maximum available light
for the autofocus system , Nikon developed a new
BriteView focusing screen for the N4004 view -
finder. It permits more light to be deflected to the
autofocus sensor for superior autofocus , without
compromising finder image Quality or manual
focusing characteristics .