7. Aperture, Exposure 'S Other Half - Canon AE-1 PROGRAM Instructions Manual

17. Aperture, Exposure's Other Half
Maximum Aperture
(large f/stop)
Note: The smaller the the
Minimum Aperture
(small f/stop)
[Example Shown: FD 50mm f/1.4. Maximum and minimum apertures differ depending on lens]
The lens has diaphragm blades. They open and
close to form certain-sized holes, or apertures,
which control the amount of light allowed to
expose the
f~m.
The aperture scale can be found
on the lens' aperture ring. The numbers on the
scale are called f-numbers or f / stops.
When taking pictures using shutter-speed
priority AE or programmed AE, the lens' aper-
ture ring must be set to the "A" mark. With the
lens on this setting, the AE-1 PROGRAM auto-
matically selects the correct aperture, based on
lighting, the film speed, and the shutter speed .
When you press the shutter button halfway, the
f / stop the AE-1 PROGRAM has set auto-
47
mati cally appears in the viewfinder. Because the
meter reads light continuously, as the lighting
conditions change, the different apertures
which compensate for the change appear in the
viewfinder. The AE-1 PROGRAM does not fix
the aperture until you press the shutter button to
take the picture.
In addition to controlling the quantity of light.
the aperture influences depth of field which, in
turn, affects the way a picture will look. When
your subject is in focus, there is a certain area in
front of it and behind it which will also be in
focus. This range of sharpness is called depth of
field.