Not quite camera lenses - but my outdoor shop (Lauche & Maas) has the habit of writing nice little essays to explain why the three-star item costs thrice as much as the one-star item, but gives so much better value, and they explain why a good telescope costs several hundred Euros instead of 20 with sharpness and low-light: looking at a fence-post in twilight, a good lens will show a sharp line and lots of light, the cheap glass will show a blurry line in low light.