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Everything You Should Know about Micro Four Thirds Mirrorless Cameras

By Loyd Case

Of all the mirrorless cameras in the market, one standard stands out as having the most substantial lens ecosystem: Micro Four Thirds. Since both Panasonic and Olympus support Micro Four Thirds, there’s a wide array of lenses available. But what is Micro Four Thirds, and where does it fit into the larger mirrorless camera market?

While DSLRs get the lion’s share of the sales for interchangeable lens cameras, mirrorless cameras often get more attention. Maybe it’s their petite size, like the recently shipping Panasonic GM1. Maybe it’s the ability to cram a 36 megapixel full frame sensor into a relatively compact body, as with Sony’s new Alpha 7 series. Pro photographers often use Fuji X-series mirrorless cameras as backups to their normal DSLR rigs. Whether its size, technology or marketing, mirrorless cameras are the hot trend in photography.

DSLRs are bulky, because they require substantial interior space for the flipping mirror and the pentaprism or pentamirror. It’s true that companies have been putting DSLRs on a diet, like Canon’s EOS SL1, but the SL1 is a fairly stripped down, entry level camera. Enthusiast or pro DSLRs tend to be more bulky, like the EOS 6D that Norm’s been using lately. I’ve carried Nikon DSLRs for years, most recently the Nikon D600 full frame DSLR. But I yearned for something more compact and lighter. But I’d become attached to the rich ecosystem of lens possibilities with Nikon’s F-mount.

Shooting with a full frame Nikon DSLR gave me nearly unlimited lens possibilities.

Of all the mirrorless cameras in the market, one standard stands out as having the most substantial lens ecosystem: Micro Four Thirds. Since both Panasonic and Olympus support Micro Four Thirds, there’s a wide array of lenses available. But what is Micro Four Thirds, and where does it fit into the larger mirrorless camera market?

Four Thirds begets Micro Four Thirds

Relative sensor sizes compared to 35mm “full frame” (the blue rectangle.) Four thirds offers a roughly 2x crop factor. (Credit: Wikimedia Commons)

The original Four Thirds, launched in 2001, created a standard sensor size and aspect ratio. The sensor size is roughly half the area of a typical full-frame DSLR sensor. The aspect ratio of 4:3 (hence “Four Thirds” is similar to some types of medium format cameras and makes printing on standard 8 x 10 photo paper easier. Four Thirds was designed from the ground up to be a purely digital standard.

When Four Thirds launched, a number of companies joined the bandwagon. Olympus and Kodak were the key developers of the standard, but Panasonic and Leica also shipped Four Thirds bodies. These were DSLRs, complete with flipping mirrors and pentaprisms. At the time Four Thirds launched, Olympus viewed the standard as the next generation of professional cameras. Consequently, they developed a rich set of lenses which are still available, some of which are equal to or better than the best Nikon or Canon lenses. Since the sensor offered a 2x crop factor, lenses could be more compact and lighter.

In reality, Four Thirds never really took hold among pro photographers. The biggest guns in the professional camera field, Canon and Nikon, stuck with DSLRs, and relatively few pros picked up on the new standard. Sensor technology was an impediment: a decade ago, small sensors meant poor low-light performance. Olympus made up for this by offering a number of f/2.0 and faster lenses, but these were expensive, and building f/2.0 capable zoom lenses meant that they weren’t as small as they could have been.

In 2008, Panasonic and Olympus developed a new standard, Micro Four Thirds, often abbreviated to Micro 4/3. The sensor size and aspect ratio is the same, but the standard was designed for mirrorless bodies. This allowed the two companies to shrink the bodies even more, but did change the distance from the inner lens surface to the sensor (the flange distance) from the original Four Thirds standard. Micro 4/3 cameras can still use older Four Thirds lenses, but an adapter is needed to extend the length from rear element to the sensor.

Micro Four Thirds enables more compact form factors, like this Olympus E-PM2 aka the Pen Mini.

The first generation of mirrorless cameras offered contrast detection autofocus. Contrast detection can be fast and accurate as long as the subject isn’t moving. Contrast detection measures the contrast (intensity differences) between adjacent pixels; best focus is achieved when the maximum intensity difference is measured. However, there are problems tracking fast moving subjects. To quote Wikipedia:

This creates significant challenges when tracking moving subjects, since a loss of contrast gives no indication of the direction of motion towards or away from the camera.“

When shooting with DSLRs using the viewfinder, a technology called phase detection autofocus is used. The AF detectors are actually a number of small sensors built into the camera body (usually the bottom), and haven’t traditionally been part of the sensor itself. The light beam is split by the partially transparent mirror, and directed towards the AF sensors. Algorithms compare the images at the different AF sensors, and when they match, the image is considered to be in focus. This is similar to how focusing in rangefinders work, which is why phase detection works well when tracking moving objects. The problem with phase detection as implemented using separate sensors is that lenses often need to be calibrated to achieve perfect focus, since the AF sensors are separate from the main camera sensor.

Newer sensor technology builds phase detection sites onto the sensor itself, which substantially improves tracking AF. The spanking new Olympus OM-D EM-1 has 37 phase detection sites (non-cross type), designed to work when older Four Thirds lenses are attached (via an adapter) or when using tracking (continuous) AF. However, these on-sensor sites are not cross-type.

The spiffy new Olympus OM-D EM-1 offers both contrast and phase detection autofocus, a rarity in the mirrorless world.

The Micro Four Thirds Lens Ecosystem

Micro Four Thirds was first envisioned as a way to build compact cameras that would rival high end point-and-shoot or low end DSLRs. As Olympus and Panasonic moved forward, higher end u4/3rds bodies began appearing, including Panasonic’s Lumix GH3 and the Olympus OM-D EM-5. Even retro-rangefinder style bodies had high end options, like the new Olympus E-P5 and Pansonic’s spiffy looking Lumix GX7.

On-sensor phase detection with the EM-1 makes older Olympus M.Zuiko lenses designed for the Four Thirds SLR line more accessible.

The problem for higher end photographers is that high end lenses were slow to emerge. Eventually, lenses like the Panasonic Leica 25mm f/1.4 came out. But while optical quality was good, other features requested by professional photographers, like weather sealing, was absent. Pro grade lenses on u4/3rds are finally starting to ship in serious numbers, however. Panasonic’s 12-35 f/2.8 zoom and the new Olympus 12-40 f/2.8 are both optically sharp, weather sealed and yet still compact and lighter than the full frame equivalents.

On-sensor phase detection with the EM-1 makes older Olympus M.Zuiko lenses designed for the Four Thirds SLR line more accessible. While you could always slap an adapter on an Olympus body to get the correct flange distance, contrast detection AF using lenses optimized for phase detection AF was slow and unsuitable for fast action. Autofocus is much crisper with the older Four Thirds lenses attached to the EM-1 via an Olympus MMF-3 adapter. The downside: the MMF-3 itself isn’t weather-sealed (though it’s “splash resistant”), unlike the EM-1 body and many of the high end M.Zuiko lenses.

The MMF-3 allows older Four Thirds SLR lenses to be used with u4/3rds bodies.

Now that Olympus has dropped its Four Thirds SLR line, the company is moving forward with additional pro grade lenses. The 12-40mm f/2.8 is the first in the line. Olympus announced a 40-150 f/2.8 simultaneously with the OM-D EM-1 launch, and that f/2.8 superzoom will ship in 2014.

Panasonic’s been a bit more aggressive with higher end lenses. In addition to the earlier mentioned 12-35 f/2.8, Panasonic also has the 35-100mm f/2.8 and the ultra-wide 7-14mm f/4. Coming next year is the fast Panasonic Leica DG Nocticron f/1.2 42.5mm lens. In addition, third party lenses are becoming more available from companies like Sigma, Rokinon/Samyang, Bower and others.

Shooting with Micro Four Thirds

I’ve used a number of Micro Four Thirds cameras, including the Olympus PEN E-PL5, Panasonic G5 and most recently, the Olympus OM-D EM-1.

Choosing the OM-D EM-1 was almost a no-brainer, once I figured out the tradeoffs I was willing to accept. In fact, the OM-D EM-1 is now my primary photographic tool of choice. I’m not alone; The Wirecutter calls the EM-1 the “best mirrorless camera over $1,000.” Digital Photography Review gave the OM-D EM-1 as one their “gear of the year” awards.

Coming from a full-frame Nikon D600 to the EM-1 did require some adjustments to how I shoot. It’s worth looking at what you give up when moving to a smaller format.

Shallower Depth of Field

This is perhaps the biggest deal. Full frame and APC-size sensors allow you to manipulate depth of field (DoF) in a more substantial way than u4/3rds, particularly when coupled with a wide aperture lens. Here are a couple of shots, one with a Nikon D600 using the 50mm f/1.4G shot at f/2.8 and the other using the OM-D EM-1 with a 14-54mm f/2.8-3.5 at f/2.9. Both were shot roughly 18-inches away from the figurine, the minimum focusing distance of Nikon’s f/1.4G lens.

Photo with my old Nikon. Note the sharpness of the face versus how blurry the tail is at f/2.8.

The face of the lion is sharp, but the tail is quite out of focus. The focus point was set right on the right eye of the figurine.

Shot with my Olympus OM-D EM-1, at F/2.9. The tail is a bit sharper.

The tail is still out of focus, but not quite as desirably blurry as with the Nikon.

These shots were processed quickly in LIghtroom 5.3, so there are some differences in color, exposure and white balance; the lenses were quite different as well. The point here is the difference in DoF. Sensor size is only one aspect of depth of field; by creative use of lenses plus changing the distance from the subject, you can usually achieve the effect you want. All things equal, figure that DoF effects are roughly 2x different; that is, shooting a u4/3rds camera at f/2.8 achieves roughly the same DoF effect as shooting at f/5.6 on a full frame. The kicker is that phrase “all things equal.”

OM-D EM-1 using a 12-40 f/2.8 @ f/5.6, 1/100th. By using the zoom and adjusting the distance of the background, you can still achieve desired background defocusing as needed.

Low Light Performance

This is less of an issue than it used to be, as sensor technology has improved, but smaller, higher density sensors do exhibit higher signal to noise ratio. The OM-D EM-1’s signal-to-noise ratio (SNR) at different ISO settings still trails the best APC-size sensors by a bit. You need to keep that in mind when shooting at high ISOs, particularly with raw images. The in-camera noise reduction for JPEGs is startlingly good on the EM-1, however, so shooting with JPEG is a good option at high ISOs.

Shot with the OM-D EM-1 at ISO 4000 using the 14-150mm f/3.5-5.6 consumer zoom. Converted into JPEG in Lightroom 5.3, no noise reduction applied.

Continuous Autofocus Tracking

When shooting action photos, whether it’s birds in flight, fast cars moving around a track or volleyball players lining up a kill, you need good continuous AF tracking. Most Nikons and Canons have this in spades, particularly in the full-frame bodies. The smaller u4/3rds cameras that offered only contrast autofocus had pretty significant issues with AF tracking. The OM-D EM-1 enables its phase detection capabilities when you turn on continuous AF tracking. I haven’t had much chance to use continuous AF tracking, but seems substantially better than my past experiences with u4/3rds cameras, but still not quite up to par with Nikon’s. On the other hand, the EM-1 shoots at 6 fps with image preview and up to 10 fps without image preview, which helps.

Bulk and Weight

The OM-D EM-1 has almost all the features an enthusiast or pro photographer would want. It also weighs just 505 grams.

The OM-D EM-1 weighs 359g less than the D600 – more than 3/4 pound less.

That difference in bulk and weight translates to lenses as well. The 12-80mm f/2.8 Olympus u4/3 lens weighs 382 grams. Contrast that with the 900 grams of the Nikkor 24-70mm f/2.8 lens I lugged around with various camera bodies for years. That’s more than a pound of glass lost for equivalent performance.

That said, mass can sometimes be useful. I’ve had to concentrate more on steadying the EM-1 more; the EM-1’s light weight seems to magnify small hand movements. I’ve noticed this is less of an issue with a slightly heftier lens, like the M.Zuiko 14-54 f/2.8-3.5. The good news is that the built-in 5-axis in-body stabilization (IBIS) seems to work pretty well.

It’s About the Photographs

Enough about the tech. As with most tech gear, enthusiasts can wax eloquently about their favorite gear. What it all really comes down to is the photographs. In the end, a camera is just a tool to capture images. How you use that tool is your measure as a photographer, not the tool itself.

OM-D EM-1, Zuiko 35mm macro @ f/3.5, 1/400th, ISO 400

What is true is that I can carry the EM-1 without thinking about it nearly as much as lugging the full frame D600 and a big lens. The camera almost disappears when I sling it over my shoulder, but it’s readily available when I want it.

Street photography using OM-D EM-1 using an Olympus 14-150 f/3.5-5.6 zoom.

Photography also consists of tools other than cameras and lenses. Imaging software, like Lightroom and Aperture, are essential tools for today’s photographers.

OM-D EM-1, 14-150mm f/3.5-5.6, using Lightroom to convert to black and white.

In the end, photographs are about stories, not about cameras. Whether you’re carrying around a full frame DSLR, a u4/3rds rangefinder style camera or using a mobile phone, try to tell a story with your photography. Capture a moment. See the world through your lens, whatever form that takes.