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Theia Technologies is an award-winning American optics design and manufacturing company known for quality and innovation. Theia provides high performance lenses for a wide range of applications including machine vision, factory automation, video surveillance and intelligent traffic systems. Theia’s patented Linear Optical Technology® provides ultra-wide angle lenses without barrel distortion using all-optical distortion correction. Theia’s family of high-resolution telephoto lenses are perfect f

Content Filed Under:

Industry:
Security/Surveillance Security/Surveillance

Application:
Surveillance Surveillance

Lens Resolution with Linear Optical Technology™

POSTED 09/13/2019

| By: Mark Peterson, VP Advanced Technology

Rectilinear lenses, like those made for the security industry by Theia Technologies, keep straight lines in the real world straight on the image sensor. This creates an effect called 3D stretching or lean-over in which objects at the image edge seem to be stretched because they are being “flattened” onto a plane along the tangent angle from the lens. The wider the field of view (for rectilinear lenses), the more noticeable this effect. There is an additional benefit in increased resolution at the edges of the image because of 3D stretching.

Objects in a plane

With a rectilinear lens, for objects all in the same plane perpendicular to the camera, the resolution is the same at the center and edge, even though the objects at the edges are much farther away from the camera. This is shown in the diagram below.

For example, if you need 20 pixels per foot and are using a 5MPix camera, the camera would be 37 feet away from an object in the center of the image (using the SY110 lens). As the object moves in a straight line as shown by the “object plane” in the diagram above, the resolution will remain 20 pixels per foot even though the object is getting farther from the camera. This is shown in the composite image below as well. The resolution of all other wide angle lenses will decrease as the object moves along this line.

Objects in a circle

With a rectilinear lens, resolution of objects in a circle with the camera at the center is a little more complicated. Resolution at the edge of the image as a function of straight-line distance is greater than the resolution at the center of the image at the same straight-line distance. This is shown in the diagram below.

For example, if you need 20 pixels per foot at the image center and are using a 5MPix camera with the SY110 lens, the camera should be 37 feet away. As the object moves in an arc maintaining the 37 feet to the camera, the resolution will increase towards the edge (i.e. the object will cover more pixels in the image, thus appearing to stretch) reaching a maximum of 35 pixels per foot.

Theia Lenses Resolution Performance

Resolution calculation

This formula is used to calculate the image resolution in pixels per foot for a given camera resolution and camera distance. These formulas calculate the horizontal field of view, the lens focal length, and the resolution at the image center as reflected in the above graphs.

Equation Example

Image width is 80 feet

Distance to subject is 23 feet

5Mpix chip width

#pixels for 5 Mpix chip

Result for 5Mpix camera and SY110 lens:

120° wide at 23 feet = 32 pix/foot for a 1.66mm focal length

Resolution will be in pixels per foot if you specify the distance to the image in feet (in pixels per meter if you use a distance in meters).

Lens SY110

Camera 1.3MPix 2MPix* 3MPix* 5MPix

Chip size 1/3” 1/2” 1/2” 1/2.5”

Chip_width 4.8mm 6.4mm 6.4mm 5.76mm