Oldelft was founded in 1939 as Van Leer NV's Optical Industry by Oscar van Leer. The company was originally located at the Oude Delft in Delft as an optical and fine mechanical plant .
Soon after the occupation of the Netherlands by the Nazi regime, the companies that Van Leer's possessed, were taken, because they were of Jewish descent. The company was given the name NV Optische Industrie "De Oude Delft". The activities were expanded and were both medical, defense and industrial products developed.
In 1970, Delft Electronic Products (DEP) was established and a plant in Roden was brought into production. There were and are intensifiers developed and manufactured.
In 1985 the company name changed to Oldelft Group, IPO followed in 1989 and in 1990 merged Oldelft with Enraf-Nonius to Delft Instruments.
N.V. optische industrie "DE OUDE DELFT" in Delft Holland, ("Oldelft" ), developed a range of small mirror spotting telescopes.
They started in 1941 and ceased production in 1953. Most were sold from 1946 unto 1950.
The productioncode was: SLK, what stands for (S)Sterker=Stronger,(L) Lichter= Lighter, (K) Kleiner= Smaller.
In production were:
the SLK 12 x 35, as a monocular, but also as a binocular (1948)
Other types of SLK monoculars were:
SLK 12 x 40, SLK 14 x 40, SLK 20 x 50, SLK 22x 60, SLK 24 x 60, and the Variotel SLK 6 x 16/ 24 x 60 ( the "Gummilens")
The total production of these small mirror telescopes is an estimated one thousand.