Retrofocus

How it works

A simple 24mm lens would need its rear element about 24mm from the film, which is inside the space a reflex mirror needs to swing. The negative front group pushes the required clearance back, at the cost of size, weight, and element count.

This is why vintage SLR wide angles are physically larger than rangefinder lenses of the same focal length, and why they were harder to correct for distortion and edge sharpness.

Zeiss used the Distagon name in the West and Flektogon in Jena. Both appear in this catalog and both are retrofocus designs.

Why it matters when buying

Retrofocus wides adapt to mirrorless without any optical compromise, because the adapter only adds the flange distance the design already expected. They are among the safest vintage wides to adapt.