Glossary
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
How it works
The design places two nearly mirror-image halves around the aperture, which cancels several aberrations automatically and makes it possible to reach f/2 and faster with good correction across the frame.
Zeiss commercialized it as the Planar, and the fast variant became the Biotar. Nearly every 50mm and 58mm lens in this catalog is a descendant, including the Helios 44 series, the Takumars, the Rokkors, and the Canon FD fifties.
Very fast Double Gauss lenses trade correction for speed. Wide open they show a soft glow from residual spherical aberration and swirl from mechanical vignetting; by two stops down they are typically sharp and contrasty.
Why it matters when buying
If a listing calls a lens six elements in four groups and it opens to f/2 or faster, expect the familiar behavior: dreamy wide open, sharp by f/4, pleasant transition in between.
Lenses that show it
Asahi Pentax
Super-Multi-Coated Takumar 50mm f/1.4
50mmf/1.4M42
- Used value
- $70 to $240
- Made
- 1971-1975
Asahi Pentax
Super-Takumar 50mm f/1.4
50mmf/1.4M42
- Used value
- $80 to $400
- Made
- 1964-1971
Asahi Pentax
Super-Takumar 55mm f/1.8
55mmf/1.8M42
- Used value
- $35 to $130
- Made
- 1958-1971
Canon
FD 50mm f/1.4 S.S.C.
50mmf/1.4Canon FD
- Used value
- $55 to $200
- Made
- 1971-1990s
Canon
FD 55mm f/1.2 S.S.C.
55mmf/1.2Canon FD
- Used value
- $180 to $600
- Made
- 1973-1979
Canon
FD 85mm f/1.8 S.S.C.
85mmf/1.8Canon FD
- Used value
- $100 to $340
- Made
- 1974-1990s