Key Takeaways

  • A scientific institute faced distortion and chromatic aberration issues in high-performance lenses, affecting image quality and accuracy for scientific observation.
  • Avantier crafted a fisheye lens with controlled F-θ distortion (<2%) and chromatic aberration (<0.04mm). The lens ensured accurate target acquisition and maintained high image quality, eliminating the need for distortion correction.
  • Achieving an excellent optical resolution, the lens exhibited MTF values surpassing 0.2 at 200lp/mm, 0.3 at 160lp/mm, and 0.5 at 120lp/mm.
  • Avantier’s fisheye lens met diverse application needs, garnering trust for its design prowess and high-quality products in scientific, military, and consumer fields.

 

A scientific research institute approached Avantier to manufacture custom lenses. This research organization uses high-performance lenses for scientific observation and research, and high image quality and accuracy were required. However, the customer was having problems with distortion and chromatic aberration with conventional lenses, which affected image quality and consistency in situations where high quality images and accurate positional information were required.

Avantier therefore offered this type of lens.

Fisheye Lenses
Figure 1. Shaded Model
Fisheye Lenses
Figure 2. Lens Layout

The picture above is a wide spectrum fisheye lens from SO. This lens has a visible spectrum with focal length of 1.2mm, F number of 2.8, and Field of view of 175°.

Fisheye Lenses
Figure 3
Fisheye Lenses
Figure 4
Fisheye Lenses
Figure 5. FFT Surface MTF

By controlling the F-θ distortion under 2%, the system can accurately acquire the target position information from the image, which the image quality has a spot RMS radius smaller than a pixel size within 95% of the field of view. At 200lp/mm, each FOV has MTF larger than 0.2, 160lp/mm has MTF larger than 0.3, and 120lp/mm has MTF larger than 0.5. Overall, this lens has excellent optical resolution that is close to the diffraction limit.

Fisheye Lenses
Figure 6. Field Curvature and Distortion

Distortion means the loss of similarity between the image and the object. This is mainly due to the image magnification changed after the enlargement of the FOV. According to aberration theoretical analysis, distortion is proportional to the FOV power of three. This is mainly depending on the action of the principal ray, which only affects the similarity between image and the object, and it will not affect the image clarity. Distortion correction will affect the astigmatism and coma aberration correction, and the presence of distortion could appropriately improve the image uniformity, therefore distortion correction is not needed.

Fisheye Lenses
Figure 7. Relative Illumination Curve

For Fisheye lens, because of the existence of aperture aberration, relative illumination on the edges is slightly higher than the center. Due to the need of aberration correction, when appropriately adjusting the vignetting can effectively improve the image quality, but at the same time will decrease the illumination on edges. As shown in the above image, the relative imagine of the image plane is higher than 90%, and the curve shows at least 0.9 and higher in the entire field of view. This indicates the image plane has very good illumination uniformity.

Fisheye Lenses
Figure 8. Longitudinal Aberration

Chromatic aberration can be controlled within the range of 0.04mm, which the secondary spectrum is relatively small and can be meeting the needs of practical application.

Fisheye Lenses
Figure 9. Lateral Color

As show in the above image, the lateral color is within airy radius, and the chromatic aberration dispersion spot is within a pixel range. The lateral color value is relatively small in 0.9 FOV. To ensure the image quality in the central region, the lateral color should maintain at small value from 0.9 FOV to the whole FOV.

Challenges the customer was able to solve

  • Control of F-θ distortion: The lens controls F-θ distortion to less than 2%, providing a spot RMS radius smaller than the pixel size within 95% of the field of view, allowing accurate target location information to be obtained from the image.
  • Correction of distortion: Distortion is properly corrected, eliminating the need to improve image uniformity. Especially in the case of fisheye lenses, distortion and aperture aberrations are handled to maintain high image quality relative to the image plane.
  • Chromatic aberration control: The lens controls chromatic aberration to within 0.04 mm, keeping the chromatic aberration dispersion spot within the pixel range. This ensures that chromatic aberration is never an issue and produces high quality images.

Avantier’s ability to provide lenses with this kind of performance allows customers in scientific research, military, and consumer applications to acquire high-quality images and use accurate positional information, thereby achieving success in many applications. Customers trust this product and are satisfied with our superior design capabilities and high quality products.

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Custom Fisheye Lenses at Avantier 

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Custom Fisheye Lenses at Avantier

Fisheye lenses are ultra wide angle lenses that produce a hemispherical or wide panoramic image. Images produced by fisheye lenses are highly distorted, and have a characteristic non-rectangular look with a marked absence of the straight lines of perspective  in more traditional imaging. 

At Avantier, we produce many types of custom fisheye lenses for a wide range of imaging applications.

Types of Fisheye Lenses

Fisheye lenses may be circular, full-frame (diagonal), or cropped circle (portrait).  

Circular fisheye lenses have a 180 degree angle of view. They project a hemisphere onto a circle within a frame or sensor area. The corners of an image taken with a circular fisheye lens will be completely black. 

Full frame fisheye lenses are sometimes called diagonal or rectangular fisheye lenses, and  for these lenses the image circle is circumscribed around the sensor area. The angle of view of these fisheye lenses is 180 from one corner to another. Horizontal and vertical angles of view of these lenses will be less than 180; the exact angles will depend on the lens. For example, an equisolid angle 15 mm full frame camera will have a diagonal angle of view of 180, a horizontal angle of view of 147, and a vertical angle of view of 94. 

Cropped circle fisheye lenses are, in a sense, halfway between circular fisheye lenses and full frame fisheye lenses. Here the image is optimized for the width of the format cameras, and the images will appear to be cropped at the top and bottom. This type of lens is also called a portrait fisheye lens. 

Fisheye Lenses
Fisheye Lenses
Fisheye Lenses

Fisheye Lenses

Understanding  Fisheye Lenses

While rectilinear lenses can be characterized by focal length and aperture, a fisheye lens has far more independent parameters. These include angle of view, image diameter, projection type,  mapping function and sensor.  If a fisheye lens is designed for a camera with a small sensor, it will typically have shorter focal lengths in order to maintain the extremely wide field of view of a true fisheye.

All fisheye lenses are affected by barrel distortion, which causes items in the center of the image to appear to bulge outwards. Straight lines will appear to curve. This visual distortion is expected when using fisheye lenses and is not typically considered a problem.

A fisheye lens has a large depth of field, enabling sharp focus both in the forefront and background of an image shot. This is a feature that can be used to great advantage but does eliminate the possibility of portrait-style imaging.

Applications of Fisheye Lenses

Fisheye lenses are primarily used in photography, and can produce  wide background shots and to create immersive imagery. They are also used  by scientists to capture cloud cover and document light pollution, to calculate plant canopy indices, and to evaluate near-ground solar radiation.  They can also be used in projection; planetariums, for instance,  use these lenses to project images of the night sky onto a dome.

Specifications – Fisheye Lenses

Focal Length

0.84-2.2mm

Back Focal Length

2.52-5.49mm

Aperture

>F1.4

Image Format

1/4″-1/2.3″

Resolution

>5MP

FOV

>102.5°×82.2°×61.7°

Custom Fisheye Lenses at Avantier

Avantier Inc. manufactures high quality custom fisheye lenses for imaging and projection applications. Our engineers and optical designers are available to walk you through the entire design process, and we can provide you with the precise lens you need. Whether you’re looking for a Nikon f mount look-alike to shoot circular images or an extremely wide angle lens for astronomical research, we have you covered. Contact us now to place your custom order or schedule an initial consultation.

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