Focal Reducers are the pinacle of vintage lens adapters and can set you back several hundred dollars for the purchase. Before we beging down this journey, these are mainly reserved for crop and MFT sensors on mirrorless cameras. While these seems like a very narrow audience, we find a vast majority of like minded shooters are indeed, smaller than full frame photographers.
Using a cropped sensor camera on a full frame lens allows you to use the center of the glass, the majority of people say the “sweet spot” of the lens. While this is very true and practical for sharpeness and contrast… What if you are missing wide angles or the edge bokeh characteristics of a certain lens? Then the focal reducer is for you and a much needed part of your kit.
A focal reducer is a lens adapter that is using a glass element to compress the light rays to best fit a smaller than full frame sensor, thus reducing the overall crop factor of the focal length. You are going to get all the viewing angle back but you going to get most of it back. Along the benefits of using a focal reducer is the increase of transmitted light. Because the light is being compressed, mathematicaly you can expect almost a 1 stop gain is visible, usable light. So if you are using a f1.8 aperture lens, the sensor will have aproximantly a light transimission of f1.4. This will help with manual focusing in low ambient light and keep those shutter speeds high to mitigate camera shake.
We highly recommend the Kipon Focal Reducers with the newly designed BavEyes glass element. Many of their models are in the second version, so be sure to seek those out when considering your purchase.
To work out the effective focal length of the lens, you have to do a little math. Don’t worry, it’s not complicated. The result might surprise you and you can use the majority of the beautiful character of these vintage lenses and not just the center. It will help see the swirly bokeh some lenses create, specialy toward the edged of the frame.
Main Lens Focal Length x Camera Crop Factor x Focal Reducer Factor = Effective Focal Length
Let’s use an average Pentax Super-Takumar 50mm f1.4 on a Fujifilm X-Pro3 with a Kipon Focal Reducer:
50 x 1.5 x 0.7 = 52.5mm
Here is the formula for the Mamiya-Sekor 21mm f4 on same setup:
21 x 1.5 x 0.7 = 22.05mm
And one more with the Carenar 35mm f2.8:
35 x 1.5 x 0.7 = 36.75mm
There is very little loss of the angle of view with a focal reducer and you get about an extra stop in usable light. Since these adapters do have a glass element, it’s important to spend a little more on quality lenses and construction. There are other brands at half the price that are usable that may fit your budget better, either way, using a focal reducer can get your wide angles back.
One last note, since vintage lenses are manual focus, we advise you not spending the extra money for the electronic pinned models since they will not be used.