Glossary
Haze, fungus, and separation
Haze, fungus, and separation are the three internal faults that determine whether a vintage lens is worth buying: a fine mist on the glass, a branching biological growth, and a failure of the cement between bonded elements.
Also called lens fungus, lens haze, balsam separation, lens condition
How it works
Haze is a light film, often from decades-old lubricant evaporating onto an inner surface. It lowers contrast and raises flare. A competent service usually removes it completely, so a hazy lens at a discount can be a good buy if you plan to have it cleaned.
Fungus looks like fine white branches or a spider web. It feeds on coatings and can permanently etch the glass. Light, early fungus cleans up; established fungus leaves scarring behind even after removal, and it can spread to other lenses stored nearby.
Separation appears as an irregular oily or rainbow-edged patch, usually starting at the edge of an element. It is the balsam or synthetic cement between two bonded elements letting go. It is effectively unrepairable at sane cost and it worsens over time.
Why it matters when buying
Shine a bright light through the lens from the back and look through the front. Haze is negotiable, light fungus is a risk you can price, and separation is the one to walk away from. Store lenses dry and in the light, not sealed in a damp bag.