Dalsa Falcon 4-CLHS Series User Manual

Name: Dalsa Falcon 4-CLHS Series
Brand: Dalsa
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Falcon™ 4-CLHS Series Additional Reference Information  111

Back Focal Variance when using any Filter

Inserting a filter between a lens and sensor changes the back focal point of the lens used. A

variable focus lens simply needs to be adjusted, but in the case of a fixed focus lens, the changed

focal point needs correction.

The following simplified illustration describes this but omits any discussion of the optics, physics,

and math behind the refraction of light through glass filter media.

sensor surface

(focal plane)

Focal Point with

filter is behind

sensor surface

Filter

Illustration: Change of Focal

Point with inserted filter

Incident Light

(from Lens)

In this example when a glass filter is inserted between the lens and the camera sensor, the focal

point is now about 1/3 of the filter thickness behind the sensor plane.

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