A 35mm or 50mm prime lens
Get a 35mm or 50mm prime lens to go with that new interchangeable lens camera. A prime lens is a fixed focal length lens with a fast aperture, normally an f/1.8.
If you’re used to zooming, using a prime lens sounds like a limitation, but it’s a limitation that will help you improve your photography by teaching you how to see the way a lens sees. Consider that legendary photographers like Henri Cartier-Bresson were known for shooting exclusively with prime lenses.
We suggest going with a 35mm or 50mm as these are focal lengths that more closely approximate what the human eye sees, and are easier to start with than a wide 24mm or a telephoto 85mm.