Review on Zeiss Normal Planar Manual Cameras by Janis Gailitis ᠌

Zeiss indicates aperture differently than other manufacturers: not in classic f-stops, but t-stops, as indicated by T * in the marking. This is a more "true" way to measure the light transmission of an optical system, because also takes into account the dimming that the lenses themselves give (they do not transmit 100% of light, but reflect and absorb it). Other manufacturers do not take these parameters into account (this is such a marketing ploy). For those who are interested in more about T-stops, here is an article: