Here’s a fun (though not scientific) test. One of these photos was taken with the Pentax 55mm F/1.8 c. 1976, the other the Leica Summicron 50mm F/2, c. 1969. Both taken using Leica SL2, 1600 ISO, F/5.6, at 1./50th on a tripod. Guesses which is which, A or B?
On eBay, an excellent version of the Pentax lens costs less than £60, and the Summicron north of £1000.
Click on the image to see it larger.