A teleconverter for panasonic 14-140 vii and GX7

I have been playing around with a converters lately, and one of them that I was looking for was for the Panasonic 14-140mm MKII. Through trial and errors I found out that the 14-140mm works best with a teleconverter that has a bigger rear glass diameter than the 58m filter size of the lens. The size that produced the least errors that I could find readily available has a 72mm thread for the 14-140mm zoom. So I had to use a 58mm to 72mm step up lens adapter. The actual teleconverter is a generic one, but seems to be sold under a few different names. It is listed on eBay at http://www.ebay.co.uk/itm/72MM-2-2X-Magnification-Telephoto-Lens-for-Canon-30D-40D-550D-7D-DSLR-Cameras-DV-/272263835151?hash=item3f64306e0f:g:0H8AAOSwLnBXUpyK

The reason I settled on this one is because it has metal threads, instead of plastic. It is also multi coated, can take filters and a lens hood, and doesn't cost a fortune to try out. At £18.99 it is practically a steal! I tried out some far more expensive converters that were useless on the 14-140mm zoom, but were highly rated more than a decades ago.

This teleconverter produces vignetting up to about 40mm. Between 40 to 140mm there is none that I could detect in an of my images. Chromatic aberration is hard to detect at the 40mm end, and barely visible at the 140mm end. And most, if not all, of that can be removed in Acdsee 10 pro, Photoshop CC, and LIghtroom.

The combination is not as sharp as my Pana 45-175mm with Pana LT-55 teleconverter, but it is still sharp and detailed enough to rival my 100-300mm zoom. The fact that I can use Dual IS  on the GX8 with this combination has been an added bonus. I managed to get some usable hand held test shots at 1/15s at the maximum zoom length.
The sharpest area is obviously the centre section of the lens. And I would be using this converter  mainly for birding etc where the action is normally away from the edges.
It's probably the best bargain buy of the year for me. The results exceeded all my expectations.
And now I have to offload all those Sony, Canon, Olympus, and Nikon teleconverters I also bought to try out. They were mainly designed in the late nineties and early 2000 for video cameras and small sensor digital cameras. And that showed up in my trials. Far too much CA and vignetting in all the ones I tried.