As many of you are probably aware, there is a new full frame lens to APSC mount adapter called the "Lens Turbo." This was released after the much anticipated Metabones Speed Booster. The main advantages of the Lens Turbo are that it costs under $200 and that it comes in a native K mount. I bought one one ebay and took a few test shots. Below are links to the three shots I took. They are available at full size on flickr. Only post processing was a bit of exposure adjustment, white balance fixing, and watermarking. All shots were taken with a Rokinon 85mm lens at F/1.4.
The first shot is the baseline shot with a standard PK to E-mount adapter. This is a dumb adapter with no glass. It only serves to adapt to the proper flange depth.
Original
The second shot shows the affect on depth of field and field of view when adding the Lens Turbo. For reference, the cards are spaced about 1 inch between them relative to the camera.
Lens Turbo
The final shot is also using the Lens Turbo, but this time the camera is closer to give a similar composition to the first shot.
Lens Turbo Recomposed
My observations:
The Lens Turbo maintains the central sharpness quite well. It will allow you to compose your shot from a closer distance and get a shallower depth of field. So it does what it's intended to.
Using the Lens Turbo will gather more overall light to the sensor.
Adding Lens Turbo caused camera to meter as +0.3EV vs the regular adapter in a similarly composed shot. This of course depends on how much your lens vignettes. But if you were hoping to use this specifically for it's light gathering ability, you will be let down. In other less rigorous testing, I have seen it register as +2/3 EV when adding the lens turbo. But never a full stop.
The same lens has a closer minimum focus distance with the Lens Turbo vs regular adapter.
I focused the lens with the Lens Turbo, then switched to the regular adapter. The image was then back-focused. So with the lens set to the same focus distance, the Lens Turbo actually makes it focus closer than the markings. So you should be able to focus at closer than the minimum focusing distance without the Lens Turbo.
Adding the Lens Turbo causes a shift in the distribution of focus zone in terms of in front vs behind the plane of sharpest focus.
When the Lens Turbo is used, more of the in-focus range is in front of plane of sharpest focus. For my tests, without the Lens Turbo I would estimate that the focus distribution is close to 50/50 in back of versus in front of the plane of sharpest focus. But When using the Lens Turbo, there is a noticable shift of this ratio where there is distinctly more of the acceptable focus range in front of the plane of sharpest focus versus behind it.