Just bought a Fujian CCTV 35mm lens - is there a problem with it?

Hello everyone, I've lurked the dark corners of the forums for a while and recently joined after I bought my NEX-F3. Enjoying it immensely so far, and I bought the Fujian 35mm 1.7 lens as a cheap way into manual lenses and a stopgap portrait lens.

This is where I'm having a problem: a pinkish ring appears in some photos in the middle of the picture. When I stop down it's not as bad and the effect isn't always strong, but I'm wondering if this an issue common to this model, if my particular lens is faulty or if there's anything I can do to stop this.

Here are some examples: