Vintage Lens Glossary: Terms Explained

Swirly bokeh

Swirly bokeh is the effect where out-of-focus highlights toward the edges of the frame stretch and rotate around the subject, forming a swirl.

Also called swirl bokeh, rotational bokeh, cat's eye bokeh

Bubble bokeh

Bubble bokeh is the effect where out-of-focus highlights render as discs with a bright, sharply defined outer ring, resembling soap bubbles.

Also called soap bubble bokeh

Double Gauss

A Double Gauss is a near-symmetrical lens design of six or seven elements in four to five groups, and it is the formula behind almost every fast standard lens of the twentieth century.

Also called Planar type, Biotar type

Sonnar

A Sonnar is a lens design that packs its elements into thick cemented groups, minimizing air-to-glass surfaces to gain contrast in the era before anti-reflective coatings.

Also called Sonnar formula

Retrofocus

A retrofocus lens puts a negative group in front of the main assembly so its optical center sits farther forward than its focal length, letting a wide angle clear an SLR mirror box.

Also called inverted telephoto, Distagon type, Flektogon type

Thoriated glass

Thoriated glass is optical glass containing thorium dioxide, used from the 1940s to the 1970s for its high refractive index, which is mildly radioactive and tends to yellow with age.

Also called radioactive lens, hot lens, yellowed lens

Flange focal distance

Flange focal distance is the gap between a camera's lens mounting flange and its sensor or film plane, and the difference between two mounts is exactly the thickness an adapter must add.

Also called register, flange distance, flange back distance

Infinity focus

Infinity focus means a lens can still bring very distant subjects to a sharp focus, which requires the lens to sit no farther from the sensor than its design distance.

Also called reaching infinity, infinity hard stop

Preset aperture

A preset aperture uses two rings: one sets a limit, the other opens and closes freely up to that limit, so a photographer can focus wide open and stop down to a chosen value without looking.

Also called preset lens, two-ring aperture

Crop factor

Crop factor is the ratio between a full-frame sensor's diagonal and a smaller sensor's, and multiplying a lens's focal length by it gives the field of view that lens will show on the smaller sensor.

Also called focal length multiplier, equivalent focal length

Zebra lens

A zebra lens is a Carl Zeiss Jena or Meyer-Optik lens from roughly the 1960s whose focus and aperture rings carry alternating bands of polished aluminium and black, a styling cue collectors use to date it.

Also called zebra stripe lens, zebra barrel

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

Lens coating

A lens coating is a microscopically thin layer applied to a glass surface to cut reflection, and multicoating stacks several such layers to raise transmission and suppress flare far more than a single layer can.

Also called multicoating, single coating, anti-reflective coating, T*, SMC, EBC

Aperture blades

Aperture blades are the overlapping leaves that form the opening inside a lens, and their number and condition determine the shape of out-of-focus highlights and whether the aperture works at all.

Also called diaphragm blades, blade count, oily blades

The vocabulary of old glass.