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Home > Frequently Asked Questions > Measurements > Optimizing Your Measurement > How do I determine the spot size and focal length of my setup?

How do I determine the spot size and focal length of my setup?

Collimating lens clear apertureFor a point source, near collimation can be assumed, so the beam will be the “clear” aperture of the lens. If a fiber is attached to the lens, the divergence angle can be calculated depending on the height of the fiber. This information allows you to calculate the spot size at a distance.

Tan(Theta) = (Height of fiber)/(Focal Length)

Focal Length = Height of fiber = (1/2)*core diameter

Theta = divergence angle

 

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74-series Collimating Lenses

74-series Collimating Lenses

Single and Achromatic Lenses
84-UV-25 Collimating Lens

84-UV-25 Collimating Lens

Large-Diameter Single Lens
COL-UV-30 Collimating Lens

COL-UV-30 Collimating Lens

Large-Diameter Single Lens
74-90 series Lens Holders & Mounts

74-90 series Lens Holders & Mounts

Right Angle Collimating Lens Assemblies
74-ACH Lens Holder

74-ACH Lens Holder

Adjustable Collimating Lens Holder
ACH-CUV-VAR Lens Holder

ACH-CUV-VAR Lens Holder

Adjustable Collimating Lens and Cuvette Holder