<p>I have a Xenar 50mm f2.8 lens in Exakta mount. I noticed that the front element has a number of cleaning marks. The pictures I get are really soft wide open so I wish to have it replaced. I believe my lens was made before WW2 started so the exact same lens becomes hard to find. I am wondering if there are alternative Xenar lenses elements that I can use as a replacement, for example, the Retina-Xenar 50mm f2.8. Have the Xenar 50mm designed changed over the years?</p>