Prime vs. Zoom lenses

[fmw]

Fixed focal length lenses are way easier to design because the correction of aberrations is made on a static rather than a moving target. Given comparable design, manufacturing and materials, the prime lens will be simpler with fewer elements. That results in sharper corners, less distortion, higher contrast and better resolution. It will also be smaller and lighter and focus closer and usually be faster. A high quality fixed focal length lens from 20 or 30 years ago will still outperform any zoom lens, even today's, quite noticeably.

Yes there are differing qualities of lens design, manufacturing and materials so don't forget that I'm talking about comparable elements.

Yes, there are modern design and materials that weren't available years ago. Apochromatic optical glass and asymmetrical elements are a couple of examples. These have improved both zoom and fixed focal length lenses. However, the improvements aren't enough to make up the difference between a high quality fixed lens from a couple of decades ago and today's zooms despite the fact that both are better today than they were then.

Most fixed designs are at least 10 years old. The manufacturers don't spend much time on fixed lens designs any longer since few people buy them for digital and 35mm.