How Much Bokeh Do You Lose When Leaving Full Frame

· 29.December.2016

I remember my first photography mentor explaining to me the “necessity” of a full frame sensor. I was promised sharper images, less noise, and smeary backgrounds that would help isolate subjects. I rather blindly made the leap, quickly falling in love with the expanded capabilities. I spent 5 years accustomed to the benefits, and internally scoffed at the idea of using a lowly APS-C body for any work. Then there was a rumble in the photography industry, one that had no clunky mirrors. Sale forums were quickly becoming littered with listings of complete sets of gear. Somewhere in the comments  was the recurring explanation, “I switched to Fuji”.

I began researching, and found the same list of benefits that had others jumping ship. Lighter weight, smaller lenses, quiet shutters and, oh…a cropped sensor. I hesitated for a while, but it only took one BBQ lunch with Fuji fanatic Jeffrey Lewis Bennett (JLBwedding.com) before I too had a full Fujifilm lineup on the way. Even after using the X-T2 system for months, I still often find myself wondering what an image would look like had I used a full frame camera instead. While the sharpness and noise difference is negligible (read: non-existent), I know for certain that I would have more bokehlicious backgrounds. So what type of bokeh changes can we expect when switching from full frame to the APS-C sensor of the Fuji.

The Difference On Paper

A full frame sensor is 24x36mm, whereas the APS-C sensor is roughly 16x24mm. This translates to the crop sensor having 43% of the area of its bigger brother. This not only affects the Depth of Field, but the focal length of APS-C being a 1.5x it’s 35mm equivalent.

This sensor size difference (when all other things are equal) is what will dictate the amount of area in focus, as well as the size of the bokeh in the out of focus area. Lets consider using a Fuji body with the 56mm f/1.2 lens, and a full-frame Canon with the equivalent focal length 85mm f/1.2 L lens. If we use both lenses at f/1.2, shooting a stationary subject 10 feet away, from the same camera position, the only significant difference will be the depth of field.

As you can see in the example above (using http://www.dofmaster.com/dofjs.html), the Fuji + 56mm at 1.2 has a total depth of field of .45 ft, while the Canon + 85mm has a total depth of field of .29 ft. This means the Canon will drift out of focus much quicker, and everything outside the depth of field will have a softer focus, culminating in larger bokeh.

Comparing the Fuji 56mm again at 1.2, to the Nikon 85mm at f/1.8, we see that we have an almost identical depth of field (.45 ft to .44). This is about what you can expect to be the general equivalent apertures between full frame and APS-C sensors. F/1.2 is a bit of an outlier, because it lies on the less common ½ stop scale, whereas we are typically speaking in ⅓ stop measurements (1.4, 1.6, 1.8, 2 and so on). In order to create similar depth of field and bokeh, an APS-C body will need to be set at 1 full stop wider aperture than it’s full frame equivalent. This means to emulate an 85mm at f/2.8 on full frame, a crop body user would shoot at 56mm f/2.

The Difference in Photos

While there is plenty of math to explain the difference, I wondered what type of difference I would see on my images. First I wanted to look at a standard image, so I had my wife pose for a quick image, using the Nikon 50mm @ 1.4 and the Fuji 35mm (52mm equivalent) @ 1.4. Camera position and subject position stayed identical, there is a small difference from the slightly longer focal length of the Fuji lens.

Nikon D750 + 50mm @ 1.4

Fujifilm X-T2 + 35mm @F/1.4

I have to say, the difference here is very faint. While there is an overall softness to the background of the full frame image, the actual size difference in the bokeh is minimal. On top of that, the softness using the Nikon 50mm extends to the subject as well, and overall the Fuji file looks more appealing. This represents the balancing act between achieving a bokeh-filled background while retaining a sharp subject.

While that image is more representative of something I’d like to achieve with a narrow depth of field, I still wanted to see what a less busy image would show for bokeh differences. The following examples illustrate the Fuji 56mm f/1.2 and the Canon 85mm f/1.2 both at their maximum apertures. Again, both cameras were the same distance from the subject and everything else remained equal. In the second image, the bokeh size from the fuji file was outlined in red and compared to the Canon file to illustrate the size difference.

In these examples we start to see a more sizeable difference. While this isn’t scientific, I calculated the Canon bokeh to be about 30% larger in diameter than the Fuji using the brush tool size to estimate.

Final thoughts

The difference in depth of field does not prove to be significant until you reach higher focal lengths. The APS-C sensor and lenses of the Fuji system still leave plenty of room for achieving excellent bokeh. While full frame will always win the bokeh battle, you can still use other methods to increase the bokeh in your images on the Fuji system. Minimizing camera-to-subject distance and maximizing subject-to-background distance will help you achieve buttery backgrounds. Remember, bokeh only adds to an image when you start off with a tack-sharp subject. The longer total depth of field distance (in focus area) of the Fuji system is a huge advantage over full frame. Many times while working I would have to stop down my wide aperture primes for full frame, because the depth of the focus plane was so incredibly slim, my keeper rate would be very low. I found it fitting that I experienced this during the comparison test as well.  It’s important to not let the idea of a smaller sensor restrict your perceived capabilities as a photographer.

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