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

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