A prime lens has a fixed focal length. It does not zoom. You cannot change the magnification without moving your feet. That limitation is also its strength. Prime lenses are often sharper, faster, and lighter than zoom lenses at the same price. They have fewer optical elements, which means fewer compromises. A 50mm f/1.8 prime is one of the cheapest and best lenses you can buy. It is sharp, fast, and small. It is often the first lens a photographer falls in love with.

Prime lenses force you to move. You cannot stand in one place and zoom in and out. You have to walk closer or step back. That movement changes perspective, which changes the image. Prime lenses also tend to be faster, with wider maximum apertures. A fast prime is essential for low-light photography and for shallow depth of field. The trade-off is flexibility. A zoom lens can cover a range of focal lengths. A prime covers one. Photographers who shoot events or sports often prefer zooms. Photographers who shoot portraits or street often prefer primes. Both are tools. The choice depends on how you shoot.

Prime lens advantages

• Sharpness. Fewer optical compromises.
• Speed. Wider maximum apertures, better in low light.
• Size. Smaller and lighter than zooms.
• Price. Often cheaper than equivalent zooms.
• Discipline. Forces you to move and compose.

A prime lens is not better than a zoom lens. It is different. The best lens is the one that suits the way you see.