Collapsible Lens

The Summitar 50 f/2 is the predecessor of the Summicron 50mm f/2. This lens uses new glass and a new design, which brings its optical level up to a higher level than its predecessor. At the same time, it also has the same compact structure and light weight as its predecessor lens. But what really sets this lens apart is that its glass is radioactive.

Radioactive Yellow Glass

The main source of radioactivity in lenses is the use of thorium oxide as the glass component in the lens elements. Thorium oxide glass provides a high refractive index and low dispersion, which helps lens designers minimize chromatic aberration and reduce curvature. However, the presence of thorium in the glass can cause the lens elements to yellow over time.

Is Radiation?

If you use these lenses correctly, there’s no risk to your health from the thorium in the Leica Summicron 5cm lenses. I’ve got five of these lenses and I’ve measured their radiation levels one by one. The radiation levels are higher in the early stages than they are in the later stages. However, prolonged exposure to this radiation can damage the eyes and cause cataracts and other vision problems. The main source of radiation is within ten centimeters directly in front of the lens. The radiation value behind the lens is pretty much nothing.

Radioactive yellow glass serial number:
NR 920×××
NR 921×××
NR 922×××
NR 993×××
NR 994×××
NR 995×××
No. 1009×××
Nr102××××
No. 104××××

Clarity

When you stop the lens down to f/2, it delivers excellent subject separation, background blur, and low-light performance without sacrificing too much sharpness. However, if you stop the aperture down to f/4, it’s really sharp and captures all the detail you could ask for. It’s a lot better than the Summitar.