Did an Ebay search for wide converters with 62mm thread as my Canon WD-58 and step ring caused vignetting. I came across an Olympus WCON-08B with a modest .8x conversion factor, in good condition for just £30.00. Have to say it works fantastically well, with little edge distortion, and it looks good on the camera. Adds a bit of weight of course however it feels like quality glass and seems to be multicoated. I think it was designed for stills but performs admirably probably helped by being designed for a larger sensor.
Only problems was seeing the mic wind gag due to the increase angle of view, cured by re-routing the mic cable in the cable clips and applying a little tension to raise the front a tad.