From the lens side, CRA is the angle of the chief ray as it leaves the glass toward the corner of the sensor. Wide, short M12 lenses often exit steeply. Telecentric inspection lenses exit almost parallel. The sensor microlenses are built for one of those habits, not both.
In one sentence. Maximum CRA on the lens page is the steepest corner ray the glass will send. Pair it with the sensor, not with a hope.
The usual mismatch
A 1.8 mm M12 on a small BSI chip is the classic. The view is wide, the CRA is high, the corners are dark or pink, and someone adds a digital shading correction that turns noise into a flat stain. Correction can hide a little. It cannot invent photons that missed the well.
How to pair it
Same rule as the sensor CRA note, seen from the other aisle. Filter lenses by image circle first, then look at Maximum CRA. If you are on a modern small-pixel part, prefer glass that was designed for that family. If the number is missing, budget a bench test. Do not discover it on a customer line.