There used to be no contest in image quality between supertelephoto prime and zoom lenses. Zooms simply could not keep pace with primes, and if you wanted to create professional-level photos or work in demanding conditions, you had no choice but to shell out for a top-shelf prime. Supertelephoto zoom lenses have made tremendous progress in the last few years, however. So, do you still need to buy those ultra-expensive primes? This great video discusses the topic.