Sigma 18-50mm F2.8 DC DN Contemporary Zoom Lens (for E Mount)

I picked this because it packs a constant f/2.8 aperture into a genuinely small, light zoom — you get wide, standard, and short-portrait coverage in one lens instead of juggling primes. Before you buy, double-check that your camera is a Sony APS-C E-mount body, since this lens is not made for full-frame cameras, and note that it has no built-in stabilization, so your body's stabilization or steady shutter speeds will matter in low light.