Like everyone else, the old Vivitar had several levels of lenses. The older S1 lenses (NOT the current lenses) were designed to compete with the better OEM lenses and did. Today, Vivitar seems to be producing average consumer lenses at average consumer prices.
Originally Posted by jvarsoke
The 70-150 seemed to be a love-hate lens. Way back when, Modern Photo gave it a good review and I have a friend who has one and loves it, but he gets great, sharp results. The one sample I tried was terrible and I couldn't get sharp results no matter what I tried.
BTW, you might want to check out http://medfmt.8k.com/third/index.html for more third-party lens info and discussions. The Cult Classic and Third Party Mfgrs are particularly interesting.