For the data sampled in digital systems two conditions hold:

- The Signal must have a finite bandwidth: above a cutoff frequency all frequency components must be zero..
- The sampling frequency must be minimum twice the cutoff frequency of the signal.

These rules are called Shannon sampling theorem , or Nyquist Shannon Sampling Theorem.

See https://www.optowiki.info/faq/why-can-color-cameras-use-lower-resolution-lenses-than-monochrome-cameras/

This effect is called aliasing and results from mirroring of frequencies above into the frequencies below the cutoff limit..

In Optics the Nyquist-Frequency equals onle line per pixel = half a line pair per pixel.

At the Nyquist-Frequency the MTF reaches Zero. We don’t have contrast then.

The cutoff frequency depends on the FNumber and the wavelength.

One can resolve 70% of the Nyquist frequency = 0.7*Nyquist frequency = Nyquist frequency / 1.41

If you even want a chance to reach 50% contrast, you should even divide by 2.

This contrast is then reachend over a range of 4 pixels.

Lets say we have a sensor with 2.2um pixel pitch.Then the Nyquist frequency is 1/2 line pairs per Pixel.

On 1mm = 1000um fit 1000/2.2u = 454pixel.

So the Nyquist frequency = 0.5lp / pixel = (454/2) lp/mm = 227lp/mm.

there we have 0% Contrast.

To have a chance for 50% Contrast haben, we have to divide this value by 2 and get (227/2) lp/mm = 113.5 lp/mm.