The Fotodiox focal reducer is notoriously smeary at wide lens apertures, to the point of massive pre-buyer outrage, many refunds and the hasty rebadging of the first version as a "soft focus special effect" adapter. It's very possible your Nikon is better wide open than you think.
Now, I was well aware of the argy-bargy after the release of their first focal reducer/speed booster, the "Light Canon", easily identified by it's distinctive blue aperture ring. The one I bought was their identically-purposed "Excell +1", which has a red aperture ring and was meant to be an apology for the universally hated Light Cannon. In fact, when I bought the Excell +1, they sent me a copy of the blue-ringed adapter for free, having rebadged it as a "soft focus adapter". I guess the hope was that it could find a place in our hearts as a "special effect" tool. Well, I can tell you that both the red and blue versions of their Nikon-to-Canon-FD adapters can be safely rebadged as a "cataract effect" and they can find a place in a nice comfy dumpster.
|One more thin adapter was needed in order to use the good Metabones adapter on the Nikon lens. This chart should help you visualize the strategy.|
A new adapter arrived - a Nikon to Canon FD adapter. Using this, you can mount the Nikkor lens to the properly good (and way more expensive) Metabones focal reducer/speed booster/adapter-converter. Lens adapters are not like the plugs in your house. With electrical cords, plugging too many adapters into each other is a recipe for a charred, smokey Christmas. With camera lenses, as long as the light gets where it needs to be, and in proper focus, the camera doesn't care what kooky mechanism you cobbled together to make it happen.
So, put Nikon lens on Nikon-to-Canon adapter, and put Canon adapter on camera. Power on camera. I pointed the camera at a couple of random lenses on the coffee table and took some test shots. In all the pictures, the camera was sitting on the coffee table, so camera shake shouldn't be a factor. I took two shots with each adapter: one at f/2.8 and one at f/1.4, to show how the aperture effects the softness of the focus. Pay no attention to any of the writing on the lenses in the test shots. They're just there to provide some fine detail.
Wowzers. The red Fotodiox "apology adapter" is still garbage. My advice is to avoid Fotodiox's "active" adapters. Fotodiox does make lens adapters that don't have any corrective optics in them, and they may be fine. I have no idea. However, recall that I had to spend an evening carefully sanding the mounting flanges on the red Fotodiox adapter just to get it to mount to my E-M5 without fear of breaking the camera's lens mount. So, it seems that Fotodiox has difficulty in manufacturing a couple of mounting flanges that don't pose a threat to your camera. Telecinese was right. The Excell +1 really is a hopeless piece of junk.
The cheapo M42-Micro Four Thirds speed booster I bought on Ebay is still miles better than the Fotodiox. So, minor victory there. The real good news is that the 1966 Nikkor lens turned out to be way better than it originally seemed, no thanks to Fotodiox.