Fisheye Lens and Wide Angle Lens Distortion

Wide Angle Lenses and Fisheye Lenses: An Introduction

Distortion is the change in magnification and angular resolution as a function of field angle in an image.

Optical Distortion, Wide Angle, and Fisheye are used when discussing lenses that provide a large field of view.

What is Wide Angle? What is Fisheye? Is there really a Difference?

Yes, there is a difference between a fisheye and a wide-angle lens. A definition from the Smith's Modern Optical Engineering, Fourth Edition, page 718, is: 

Fisheye: A lens with a field of view of 180° or more.

Therefore, a Fisheye Lens can be a Wide Angle Lens when an image sensor smaller than the image circle is used. A Wide Angle Lens is not necessarily a Fisheye Lens.

GoPro's marketing team was stuck with "Fisheye" because the first product used a cropped Fisheye lens. The newer GoPros use Wide Angle lenses which are not Fisheye lenses.

So How Can a Fisheye Lens Be Wide Angle? But Not Vis-Versa?

Fisheye Lenses with 180°+ Field of View do not always provide 180° FoV if used with a smaller sensor.

For example, a Fisheye with Full Coverage can provide much smaller fields of view such as 160° Diagonal, where they act as a "Wide Angle" Lens.

The reason for this is the "Fisheye Fill Factor" which has six different general categories.

Wide Angle vs Fisheye Lens

Barrel Distortion as a Third Order Optical Aberration

Optical distortion is a third order transverse aberration. The simple explanation is that distortion is the change in magnification (angular resolution) versus image height.

Distortion is present in all fisheye lenses and most wide-angle lenses.

Additionally, distortion is a function of field angle, and usually increases as field increases.

Rule of Thumb 1: A lens with greater distortion has greater field of view than another lens which has the same Effective Focal Length.
Rule of Thumb 2: The smaller the field of view, the less apparent optical distortion is.

The distortion profile of a lens dramatically changes the field of view output from a camera system. In the below charts you can see that a 1.9mm lens can provide anywhere from 106° Field of View to 180°+ Field of View at 5.0mm image circle. 

Fisheye Distortion Projection Rectilinear Stereographic Equidistant Equisolid
Angular Resolution of Fisheye Lens Distortion

What is the Difference Between Perspective Distortion and Optical Distortion?

Optical distortion is a third order transverse aberration. The simple explanation is that distortion is the change in magnification (angular resolution) versus image height.

Distortion is present in all fisheye lenses and most wide-angle lenses.

Rule of Thumb 1: A lens with greater distortion has greater field of view than another lens which has the same Effective Focal Length.
Rule of Thumb 2: The smaller the field of view, the less apparent optical distortion is.

Why does Distortion Matter to Computer Vision?

Distortion changes the scale of objects at different parts of the field of view. Additionally, the scale changes both radially and tangentially, causing object deformation.

CNN-based methods should ideally be trained on data that has the distortion profile used by your embedded vision system. Otherwise, activations will occur in incorrect locations.

Distortion and Computer Vision

Pei, et. al. "Effects of Image Degradations to CNN-based Image Classification"

Distortion changes the scale radially and tangentially, causing line deformation.

Distortion and Computer Vision

Pei, et. al. "Effects of Image Degradations to CNN-based Image Classification"

Li, et.al. 2020, “ULSD: Unified Line Segment Detection across Pinhole, Fisheye, and Spherical Cameras”​ 

View Other Image Quality and Computer Vision Topics

What's Your Application? Our Lenses Cover the Spectrum.

Low Distortion 6.8mm M12 Lens

CIL068-F2.5-M12A650

Low Distortion 6.8mm M12 Lens

200°@5.7mm IP67 Fisheye M12 Lens

CIL217-F2.7-M12A650

200°@5.7mm IP67 Fisheye M12 Lens

Fast 6mm M12 Lens

CIL061-F1.9-M12B650

Fast 6mm M12 Lens

Mobile Robotics?

Find a low F# or low distortion lens to optimize your computer vision.

Factory Machine Vision?

Our cost-effective compact C-Mount lenses are designed for up to 1.1"~1.2" format global shutter sensors.

25mm C-Mount Lens 1.1" 12MP

CIL514-F2.8-CMANIR

25mm C-Mount Lens 1.1" 12MP

35mm C-Mount Lens 1.1" 12MP

CIL515-F2.8-CMANIR

35mm C-Mount Lens 1.1" 12MP

50mm C-Mount Lens 1.1" 12MP

CIL516-F2.8-CMANIR

50mm C-Mount Lens 1.1" 12MP

Small 2.5mm M12 Lens

CIL825-F2.4-M12ANIR

Small 2.5mm M12 Lens

No Distortion 4.4mm M12 Lens

CIL043-F3.2-M12B650

No Distortion 4.4mm M12 Lens

230°@4.5mm Fisheye M12 Lens

CIL213-F2.3-M12A660

230°@4.5mm Fisheye M12 Lens

Intelligent Everywhere?

Our low distortion lenses with multiple F# can be used to optimize your depth of field.

Surveillance?

Our fisheye and IR Corrected lenses are suitable for doorbell cameras and active IR illuminated scenes.

200°@6.3mm Fisheye M12 Lens

CIL219-F2.5-M12IR

200°@6.3mm Fisheye M12 Lens

186°@5.2mm IR Corrected Fisheye M12 Lens

CIL239-F2.0-M12A650

186°@5.2mm IR Corrected Fisheye M12 Lens

Low Distortion 6mm M12 Lens

CIL059-F1.7-M12B650

Low Distortion 6mm M12 Lens

188°@6.6mm IP67 M12 Fisheye

CIL222-F2.0-M12A650

188°@6.6mm IP67 M12 Fisheye

No Distortion 3.2mm Lens

CIL034-F2.3-M12B650

No Distortion 3.2mm Lens

Fast 6mm M12 Lens

CIL061-F1.9-M12B650

Fast 6mm M12 Lens

Does it Require Getting Dirty?

Our IP67 and IP69K lenses are suitable for applications exposed to the environment.

Aerial Robotics?

Our tiny lenses are ideal for collision avoidance and object recognition.

Large Format 3.5mm M12 Lens

CIL334-F2.2-M12C660

Large Format 3.5mm M12 Lens

Wide-Angle 3.5mm M12 Lens

CIL335-F1.8-M12A660

Wide-Angle 3.5mm M12 Lens

Small 3.3mm M12 Lens

CIL036-F2.2-M12A650

Small 3.3mm M12 Lens