I have read that in many cases a Tessar lens has greater contrast due to having less air to glass surfaces than a symmetrical lens. However when perusing throug h the Schneider website, I have noticed the opposite; that the Xenars have less contrast (from the MTF curves) especially at the edges of the field than the Sym mars. Does anyone want to comment as to why this is so? With modern coatings of equal quality, shouldn't the Tessar design have more contrast?