Konica made several three versions of its 35-70mm zoom in AR mount. The first was a one touch fixed f/3/.5. It is a decent performer but not the most mechanically stable. The second was two touch fixed f/4. This one is also a good performer and is much more sturdy. The third one is also a two touch but has a variable aperture of f/3.5-4.5. It has a plastic aspherical rear element. The instruction book warns against cleaning the rear element improperly. The lens is so light is doesn't feel real. The performance is good. The problem is focusing it in low light. The microprism or split image focusing aids black out. I can only use it because I have an FT-1 body with a Nikon E screen inside. The Canon 35-105/3.5-4.5 New FD also uses an aspheric element but that one is made of glass, not plastic. The design and speed allow the lens to be be much smaller and lighter than the earlier fixed f/3.5 version. It is a good performer but does not handle flare situations well. For the time being plastic elements can be part of high quality lens designs but can't replace all glass elements.