Do More Expensive Lenses Provide Better Image Quality?
While camera and lens manufacturers work hard to make lenses with minimal aberrations, the reality is that there's a market for inexpensive and midrange lenses as well as the top-of-the-line lens ranges aimed at professionals and serious photographers. Less expensive lenses generally suffer from more aberrations than the more costly lenses. So does buying a more expensive lens always provide better image quality? Not every time.
When you pay more money for a lens, you're buying features such as build quality, weatherproofing, wider maximum apertures, and improved autofocus—as well as an improvement in image quality. These features are all important, but in practice you may not notice much difference in the final image quality. This is especially likely with prime lenses, where even the cheapest models can have excellent optical quality. You're more likely to see a difference in image quality with wide-angle, super-telephoto, and zoom lenses.
A good example is the Canon EF 85 mm f1.8 and EF 85 mm f1.2 L lenses. Despite a price difference of $1,700, the reviews I've read noted very little difference in image quality. Most of the extra cost goes toward improvements in autofocus, build quality, and the larger lens elements required to obtain a maximum aperture of f1.2. The lesson is to do your homework before making a new lens purchase—the DxO Mark camera lens database is a good place to start.