A focal reducer is a little piece of magic between two lens mounts. When I had my Fuji X-E1, I used Lens Turbo exclusively with K-Mount glass (it was a travesty that I never got use the Fujinon XF 16-55 f/2.8 on it; it just had to suffice with the vintage Takumars I had). The focal reducer took the vintage lenses and gave me almost full frame coverage, with increased sharpness, and an extra stop of light. That combination provided some of my favorite shots to date.
Since I needed more from my camera and I ended up selling the X-E1 and Lens Turbo and replaced it with a Nikon D3300. In my desire to have that bokeh-rific look that the focal reducer gave me, I found an option to mount a Nikon lens to the EOS-M. Here are some sample shots of the Nikon DX 18-55mm (the only lens I had at the time) mounted to my EOS-M.
Kit lenses typically get a bad rep; complaints range from the plastic bodies, flimsy lens mounts, and poor optics (probably the biggest complaint is that aperture range just doesn’t give enough bokeh). Photographers crave shallow depth of field and use that to justify buying bigger and better lenses. With the focal reducer, I can turn my kit lens into an equivalent 20-63mm f/2.4-4 lens without spending a ton of money.
Since crop lenses (DX or EF-S) usually produce an image circle slightly larger than the sensor size, using a focal reducer with a crop lens can still help you obtain that extra stop of light with only slight vignetting at certain focal lengths (for that full frame look without a full frame lens).
Focal reducers do not give you a 1:1 ratio like the Sony A7 II‘s full frame, it’s more like a 1:0.72 ratio. This results in a slightly longer than full frame look. APS-C users will have almost full frame coverage with a crop factor of 1.08 (or 1.152 for Canon). Micro 4/3 users, on the other hand, will have slightly larger than APS-C coverage at 1.44x crop due to their original 2x crop factor. This short teleconverter aspect of focal reducers can make mounting crop lenses to mirrorless cameras usable.
Since purchasing the focal reducer, I have used the Nikon glass more with the the EOS-M than the original camera I bought it for. I love the crazy shallow depth of field that the 18-55mm provides and the increased sharpness and speed of the kit lens has made it a main contender in my work.
If you are interested, you can find a focal reducer for your mirrorless camera here. Have any questions about the set-up or comments? Please leave them below.