Leica Summicron 50mm f/2 I (Collapsible)

The Leica Summicron 50mm f/2 Version 1, widely known as the "Collapsible Summicron," is a landmark rangefinder lens produced by Ernst Leitz Wetzlar from 1953 to 1960. As the successor to the Summitar, it was the first optic to carry the "Summicron" designation, a name that became synonymous with the f/2 aperture optics in the Leica system. The lens is celebrated for its dense mechanical construction and its ability to retract into the camera body, making a full-frame Leica setup pocketable.

Optical Design and Rendering

The Version 1 utilizes a classic double-Gauss optical design comprising seven elements in six groups. A major evolution from the preceding Summitar was the introduction of an air-spaced front element, which significantly improved the correction of coma and astigmatism while increasing overall resolving power.

The rendering is distinctively vintage. At the maximum aperture of f/2, the lens exhibits moderate spherical aberration, creating a soft "glow" around high-contrast edges that is highly prized for portraiture. When stopped down to f/4, the resolution increases drastically, delivering sharpness that rivals many modern optics. The aperture diaphragm consists of 10 blades, producing a nearly circular opening for smooth out-of-focus backgrounds.

Radioactive Thorium Elements

A defining characteristic of early production units (typically those with serial numbers below 1.1 million) is the use of radioactive thorium oxide in the glass elements. Leitz utilized thorium to achieve a high refractive index with low dispersion.

Over decades, the radiation causes the glass to amber or yellow.

• Black & White Photography: This yellowing acts as a natural high-quality contrast filter, darkening blue skies and separating tones.
• Color Photography: It imparts a strong, warm vintage cast (which can be reversed by prolonged exposure to UV light).

Mechanical Construction

The lens barrel is machined from heavy brass with a satin chrome finish (rare screw mount and fixed versions exist), giving it a dense, premium tactile feel. The focus ring features a spring-loaded infinity lock—a quirk of the era.

Digital Camera Warning: While the collapsible design is safe for film bodies (M3, M6, etc.), extreme caution is required on digital Leicas (M9, M10, M11, SL). The sensor stack on digital cameras is thicker than film; fully collapsing the lens can cause the rear element to strike the sensor or shutter. Many users employ a rubber O-ring on the barrel to limit the collapse depth for safe digital use.

Comparison to Related Lenses

Thypoch Eureka 50mm f/2

Released in 2024, the Thypoch Eureka is a modern tribute to this specific lens. While it mimics the collapsible mechanism and aesthetic:

• Weight: The Eureka is aluminum and significantly lighter than the brass Summicron.
• Optics: The Eureka uses modern glass and coatings, offering higher contrast and flare resistance but lacking the "glow" and radioactive character of the original.
• Focus: The Eureka focuses down to ~0.9m, whereas the Summicron V1 is limited to 1m.

Summicron Rigid (V2) and Dual Range (DR)

The "Rigid" and "Dual Range" Summicrons followed the V1. They utilize a nearly identical optical formula but housed in non-collapsible, rigid barrels.

• The Rigid is preferred by users who dislike the wobbly feel of a 50-year-old collapsible mechanism.
• The Dual Range (DR) features a specialized cam for close-focusing work but is often incompatible with modern digital bodies due to mounting restrictions.

Summicron V3, V4, and V5

Later generations marked a departure from the classic look.

• V3 (1969): Introduced a simplified 6-element design with higher contrast.
• V4/V5: Known for high micro-contrast and clinical sharpness. They are technically "better" lenses but lack the specific spherical aberrations that give the V1 its romantic, atmospheric signature.