I·
• Through- The-Lens Exposure Measurement
G
(A)
(6)
(C)
(D)
(E)
Zooming lenses
Half-Mirror
,
Diaphragm
Moster lenses
Spindle Shutter
(F) Prism
(G) Compensating Filter For ASA
Changes
(H) Codmium Sulphide Cell
(I) Film Plane
"TTl" (through-the-Iens) is the ultimate in accurote ex-
posure measurement. With the CdS meter positioned be-
hind the lens, it meosures only the light passing through
the lens and striking the film plene. Measurement is con-
tinuous and, even as you film, the diaphragm opens or
closes constantly and automatically in response to varying
light.
How "TTL" Works
light passing through the zoom lens (A) is divided by the
half-mirror (6) port entering the viewfinder and port going
toward the film plane. The half-mirror is designed to
eliminate loss of light in the finder.
The light going toward the film plane posses the diaphragm
(C) and the master lenses (D) before recching the film
plane (I). The spindle shutter (E) is located immediately
before the film plane and has a conical surface with a
special mirror-like coating. light hitting this mirror-like
coating (E) changes its direction 90· and is thus aimed
at the CdS cell (H) through the prism (F). The compen-
sating filter for changes in ASA rating (G) is located in
front of the CdS cell (H) to control the amount of lighi
the cell measures. '
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