>>4485444Fringng? Lack of optical correction which allows aberrations.
What are aberrations? Normally different wavelengths of light bending at different values which means red and purple hit the sensor in slightly different areas and so on.
Vintange lenses will normally exhibit some strong fringing since they didnt quite get there yet in terms of optical engineering, but it's also why modern superzooms or teles or even your wide aperture normals are like twice the size of vintage stuff: extra elements and better engineering that requires larger glass surfaces will aid in reducing aberrations at the cost of, well, cost and size.
Purple fringing seems to be the most common but I never looked into why, just that some photography software has inbuilt adjustments specifically for it.