A vintage lens is the cheapest way to change how your photographs feel. Older glass renders differently, with softer roll-off, warmer color, and the kind of flare that modern coatings were designed to get rid of. Most people who buy one are buying it for exactly that.
Mount and adapter
Almost any old lens will work on a modern mirrorless body with the right adapter, which is a plain metal ring with no glass in it and no electronics. Match the lens mount (M42, Nikon F, Canon FD, Leica M and so on) to your camera and you’re ready to shoot. Focusing is manual. For a lot of people that turns out to be half the fun.
What to check
Hold the lens up to a light and look through it, not at it. You’re looking for three things. Haze is a soft fog on the inner glass that steals contrast. Fungus shows up as fine, web-like threads, and it will etch the coatings if it’s left alone. Separation is a rainbow shimmer at the edge where cemented elements have started to part. Then work the aperture ring. The blades should snap cleanly and look dry. Oil on the blades is common and fixable, but you want to know about it before you pay. Last, turn the focus ring. It should feel smooth and even the whole way round, not gritty and not loose.
How we vet glass
Every lens we list gets checked against the light and worked through its full range before it goes up. If there’s haze, fungus, oil, or stiffness, it’s in the description. Buy the lens for how it draws, and read the condition notes before you fall for the box.