Very rare Summitar * prototype of the later Summicron with thorium-oxide element in correct mount (diaphragm to ƒ/22), a small series of these lenses were produced for testing purposes in 1950, 3 years before the Summicron came on the market.
The introduction of the Summicron lens in 1953 can be considered one of the most important steps in the development of Leica lenses. By using high-refractive optical glass “LaK9“ – an invention from the Leitz glass laboratory – a high-performance lens with high aperture – could be realized without the need for radioactive elements. During early experiments for such a lens with a new optical formula from 1950, thorium oxyde-free Lanthanium crown glass was not yet available.
In total, 88 examples of the then so-called “Summitar *” were made, which are considered immediate precursors of the Summicron. The use of an asterisk “*” in the name (not after the serial number) of these lenses was probably chosen in order to identify them as containing a radioactive element. The diaphragm stops down to f/22.