Most lens aberrations grow disproportionatetely when the aperture is doubled. When designers were still struggling to get decent performance out of an 1:2/50mm design, it seemed a bit rash to introduce a 1.5 lens.

Why Leitz have opted for the Schneider lens and did not wait for the Berek solution that was being created in the same period, is a mystery, but it might be that the introduction of the Zeiss Contax RF with a good 1.5 lens, was seen as a commercial challenge.

The performance of the lens at full aperture is however barely acceptable for the intended use. Finer detail in the centre area (about 5 mm image height) is recorded with good visibility, but the very low contrast and strong presence of coma, especially in high contrast situations reduce the useful recording capabilities.