Full-Frame vs. APS-C vs. Micro Four Thirds: Depth of Field Considerations

One of the first decisions the consumer is faced with when picking a mirrorless interchangeable lens camera (MILC) system is that of sensor size, and the decision typically boils down to full-frame vs. APSC vs. Micro Four Thirds.

While you can get excellent results with all three systems, it is important to take into account a few considerations before diving in and making an investment in a particular ecosystem of bodies and lenses.

When choosing a MILC system, don’t get too caught up on raw specs right away, but consider these two things first:

  1. What are your minimum depth of field needs, and does the system provide lenses to meet them?
  2. What maximum telephoto reach will you ever need, and are you willing to pay for it? This second consideration may be less important for some (myself included).

While crop sensor (APS-C and Micro Four Thirds) cameras look appealing for their size and weight advantages, the difference may not be so great when considering depth of field requirements.

Narrow depth of field: The Great Equalizer

Sony α7 III with Zeiss Batis 85mm f/1.8 lens; Fujifilm X-T2 with Fujinon XF 56mm f/1.2 R lens; Olympus O-MD E-M1 Mark II with Olympus M.Zuiko Digital ED 45mm f/1.2 PRO lens. Thanks to CameraSize.com for comparison images.

The image above is an example of what it might take to build a good lens/body combo for portraits requiring narrow depth of field in all three systems: full-frame, APS-C, and Micro Four Thirds, respectively.

Using the excellent DoF calculator at PhotoPills, we can get the minimum depth of field achievable for each lens/body combo at its fastest aperture, shooting a subject at a distance of 2 meters:

Full Frame
Zeiss Batis 85mm f/1.8
Fujinon XF 56mm f/1.2 R
Micro Four Thirds
M.Zuiko Digital ED 45mm f/1.2
DoF near limit 197.21 cm 197.09 cm 196.61 cm
DoF far limit 202.87 cm 202.99 cm 203.5 cm
Depth of field 5.67 cm 5.9 cm 6.89 cm
DoF in front 2.79 cm (49.29%) 2.91 cm (49.26%) 3.39 cm (49.14%)
DoF behind 2.87 cm (50.71%) 2.99 cm (50.74%) 3.5 cm (50.86%)

Here is the visual breakdown:

Field of view of 3 systems at 2 meters between camera and subject

As you can see, there is almost no DoF difference between the full-frame and APS-C system, and the Micro Four Thirds system ends up with a slightly wider depth of field. The Fujifilm APS-C system ends up beating MFT for narrow depth of field in a smaller overall form factor.

Given equivalent depth of field requirements, the physical size of bodies with lenses attached ends up being roughly the same. Smaller sensors need to compromise for intrinsically higher depth of field properties with bigger and faster glass.

Small sensor superiority (sometimes)

There are cases where small sensors, such as Micro Four Thirds and even smaller 1″ sensors have a definite advantage:

  • Macro photography, where maximizing depth of field is desirable to reduce the need for focus stacking.
  • Small, light cameras for travel and street photography, where narrow depth of field is not wanted and getting most of the picture in focus is the goal.
  • Situations where extreme telephoto reach is wanted in a small, light package (birding, deep-sky astrophotography, all-in-one superzoom systems, etc.)

What’s your end game system?

Do you need extremely narrow depth of field portraits, and crazy telephoto reach? Are you willing to pay for it? Here’s where the cost/value proposition of full frame starts to break down in a big way.

Canon EF 600mm f/4L IS II USM lens adapted to Sony α7 III body; focal-length equivalent Olympus M.Zuiko Digital ED 300mm f/4 IS PRO lens

The 600mm f/4 Canon lens above costs north of $11,000 and weighs in at about 8.6 pounds. The equivalent Olympus 300mm f/4 lens costs around $2,500 and weighs just over 3 pounds. In an extreme case like this, the size advantage of the Micro Four Thirds system starts to appear.

Keep in mind that an f/4 aperture on MFT is equivalent to f/8 on full frame, so if you need the most available light to hit your sensor at this range, MFT may not be the right choice. But for birding and other brightly-lit daytime activities, the smaller sensor should do just fine.

The APS-C middle ground

Personally, I had been using a Micro Four Thirds body (Olympus OM-D E-M5 Mark II) for about a year, and while I found it worked brilliantly about 95% of the time, I started to run up against limitations in certain shooting situations.

For example, shooting my son’s basketball game in a somewhat dimly-lit gym with the E-M5 II, I found myself wanting better low light performance and PDAF. Shooting landscapes at sunset, I felt I wasn’t able to push the shadow detail in RAW quite as much as I could with my old APS-C Nikon D7100 (this may or may not be a figment of my imagination, as the actual dynamic range values are really close).

I realize that upgrading to a new flagship MFT body would give me improved continuous autofocus, and likely better dynamic range and high ISO capabilities, but it made me question whether it was worth sticking with Micro Four Thirds as a system. While sensors continue to improve, the laws of physics dictate that MFT sensors will generally lag behind APS-C and full-frame in the latest capabilities.

These differences will not matter for most people in most shooting situations. In fact, sensor abilities alone would not be a deciding factor if I saw that MFT had a significant size advantage over APS-C—but given the focal lengths I typically shoot, the form factor differences between systems are minor.

I’m an amateur/hobbyist photographer who generally shoots family, travel, landscapes, and astrophotography, with occasional paid side gigs in product photography and real estate. An aperture of f/1.2 on APS-C provides the narrowest depth of field I would ever want, and I don’t foresee myself needing a 600mm equivalent lens for anything.

mirrorless APS-C systems: Sony, Canon, Fujifilm

Which mirrorless APS-C system?

In the mirrorless APS-C world, Sony, Fujifilm, and Canon all offer competitive systems, and as a former Nikon DSLR shooter, I’m excited to see what Nikon is working on in the mirrorless realm. Sony dominates the lineup in terms of raw specs (and will continue to do so for the foreseeable future), and Canon has been producing a new and popular mirrorless system.

However, I have decided to build a system around Fujifilm. While it feels that other companies treat their APS-C systems as beginner systems, Fujifilm is the only manufacturer that has gone all-in on APS-C, eschewing full-frame entirely and producing a series of professional-level lenses perfectly matched to their APS-C bodies and sensors.

Anyway, these comparisons aren’t meant to digress into Fujifilm fanboyism. You really can’t pick a bad mirrorless camera these days—it all comes back to your anticipated needs. Just remember to keep in mind the extremes you anticipate needing in depth of field and telephoto reach, and this will help you to pick a system that works best for you.

Which sensor size do you prefer most? Please leave a comment below.

Featured header photo by rawpixel.com on Unsplash.

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