Distortion: why is it important?

Distortion is a phenomenon inherent in real-world lenses that can significantly impact image quality and measurement accuracy. There are two different types of distortion.

With barrel distortion, image magnification decreases away from the optical axis, causing a wrapped-around effect. In contrast, pincushion distortion results in increased magnification away from the axis, bending lines inward like the edges of a pincushion.

Distortion correction is crucial, especially for telecentric lenses used in precise measurement applications. Residual distortion can affect measurement accuracy, calculated as the percentage difference between the real and expected image height.

If we define the radial distances from the image center as:

- Ra = actual Radius
- Re = expected Radius

The distortion is calculated as a function of Ra

Here, a, b, and c represent constant values defining the behavior of the distortion curve. Typically, "a" is zero since distortion is usually zero at the image center. In some cases, a third-order polynomial may be necessary for a perfect fit of the curve.

Apart from radial distortion, there is also Trapezoidal distortion, which is often referred to as "thin prism" or "keystone" and results from optical and mechanical component misalignments. This causes parallel lines in object space to converge or diverge in image space.

Telecentric lenses, like those from Opto Engineering, are optimized for green light since they lie in the center of the visible spectrum. Green light offers better resolution and achromatization, making it ideal for achieving accurate measurements.

In conclusion, understanding and correcting for distortion while utilizing green light ensures optimal performance and accuracy in telecentric lens applications.