Format,
Focal Length, Aperture
Overview
Lens format, focal length,
and aperture work together to determine the image
that a camera will capture. Each is described
separately below, but it is important to keep
in mind that a change in one of these parameters
will affect the others.
Lens Format
- Lens "format" is
the size CCD the lens was designed for. These
can be ¼", 1/3", ½",
2/3", or 1". Most Videology applications
are 1/3”.
- Larger format lenses can
be used on smaller CCD's - see "Trading
Down Lenses".
Focal
Length
- Focal length is the distance
from the "principal point" of a lens
to its focal point, expressed in millimeters
(mm).
- Focal length controls
the magnification of the image captured and the
field of view.
- Focal length can be fixed
or variable - see "Varifocal & Zoom
Lenses."
- The chart below covers
the basic information about focal length.
2.8mm |
200mm |
| "Short" Focal
length |
"Long" Focal Length |
| Lower Magnification |
Higher Magnification |
| "Wide Angle" |
"Telephoto" |
| Wider Field of
View |
Narrower Field of View |
| Greater Depth
of Field |
Less Depth of Field |
Aperture (F number)
- Aperture is a measure of the
size of the lens opening, which affects its ability
to gather light and the depth of field.
- The aperture of a lens is specified
by the f#, which is the ratio of the focal length
to the lens diameter. Thus a larger diameter lens
has a smaller f#.
- The aperture of a lens can be
fixed or adjustable.
- This chart covers basic information
about depth of field.
F1.2 |
F22 |
| "Large Aperture" |
"Small Aperture" |
| Larger Lens Opening |
Smaller Lens Opening |
| Less Depth of Field |
Greater Depth of Field |
Next - Depth
of Field
