One of the more fascinating pieces of photography equipment to emerge are the Metabones 'Speed Booster' adapters that actually refocus an image from full frame to APS-C or mirrorless size sensors. This gains 1 stop of aperture and promises a sharper image. In actual fact they are like turning a teleconverter back to front, which make sense as you lose 1 stop of aperture on a 1.5x teleconverter.
So I decided to do my own test. I reasoned that a Nikon TC-14a 1.4x teleconverter would be sufficient to replicate the effect, as reversed, the math is exactly the same as the Speed Booster adapter. (1/1.4 =0.714) I also tried it with the 1.6x TC-16a, as shown in the photo below.
Firstly I got the Sony NEX 5n, held the teleconverter backwards to it and then put in front a Nikkor 45mm f2.8 GN pancake lens. I quickly found I needed to add some length to the set up to gain correct focus, so I added in a Nikon PK-12 extension ring. Even though it was a little tricky to hand hold, to my surprise it worked! The shutter speed was higher than I predicted (suggesting a faster aperture) and the sharpness was good. Very cool! The photo of the New Years card is how it came out the camera, with the lens set at f2.8.
The extension ring added a little too much base length, as it now won't focus on infinity, but allowed closer focus than usual. As I was hand holding 3 separate components, I am sure the moved around a bit, and were not aligned properly, creating some shift in the picture like a shift lens does.
The $599 price tag is quite expensive, but I suspect Metabones will do quite well initially as there are no other adapters like it. I am sure though that copies will come out and the price will come down.