Since mirrorless cameras are a quite new product (Wikipedia says 2008), what's behind the choice of the 4:3 format (for those that use it)?

My first guess would be that 4/3 pictures are made to fit 4:3 screens, but it seems that, also with the diffusion of HDTV, the screens have been steering to 16:9 formats and wider. So why this contrast between picture formats and screens evolution?

Interesting: It seems that aspect ratio choice of photo/video devices, at least for high-end products, has been trying to stay close to the golden ratio so the 3:2 format would have been a sensible choice in that sense.

  • Your assumption is simply wrong. Three brands produce 4:3 aspect-ratio and 3 brands produce 3:2 mirrorless cameras, one brand used to have both. The first mirrorless where co-designed by Olympus and Panasonic and it is no secret that Olympus liked 4:3 images with a 2X crop, they have been doing that since the film days. – Itai Jun 5 '13 at 16:26
  • @Itai sorry, I realized that, and I tried to make it less of an assumption. But the fact that the first manufacturers made that choice remains, isn't it? – clabacchio Jun 5 '13 at 19:17

The Four Thirds standard for digital SLRs was designed by Olympus and Kodak to be the first system specifically made for digital, with high standards for telecentric lenses and other design choices for a modern era, rather than adapting a film lens mount. At the time, full-frame sensors were really out of reach in terms of cost, and the smaller sensor promised a reasonably-priced and compact system. And yes, the aspect ratio was chosen to match computer monitors and the TV screens of the time — 16:9 HDTV was not yet widespread.

Fast forward a few years. Panasonic buys in, Kodak drops out. Four thirds DSLRs are the innovators of Live View, but fail to really make a dent in the market. And at the higher end, the cameras and lenses aren't as small as hoped. So; time for something new, and the Micro Four Thirds standard is invented for mirorless, capitalizing on the sucess of Live View and carrying forward the ideas and sensor technology with refinements from lessons learned. They could have changed the sensor format at that point, but that would have made it much more expensive to retool and redesign everything.

And, in any case, those Micro Four Thirds cameras have been a big success.

But not all mirrorless cameras are Four Thirds. For example, the Samsung NX and Sony NEX (unrelated despite similar names) are APS-C, and Nikon 1 uses a smaller-than-the-four-thirds-standard 1" sensor.

  • So basically screen sizes didn't play any role in the choice of the aspect ratio... – clabacchio Jun 5 '13 at 13:02
  • I think they did in the original decision, but not in the ongoing one. Some Panasonic Micro Four Thirds cameras actually have larger sensors from which you can choose a 4:3 or 16:9 crop (along with other possibilities). – mattdm Jun 5 '13 at 13:11

I'm not sure if you are asking about the micro four thirds standard or the 4:3 aspect ratio, so I'll answer both:

  • Why do mirrorless cameras use micro four thirds?

They don't, only Panasonic and Olympus build micro four thirds cameras, there are a lot of other companies making mirrorless cameras (for example: Sony, Fujifilm, Samsung, etc.) that have other mounts.

  • Why do mirrorless cameras use 4:3 aspect ratio?

Thomas Edison's lab chose this aspect ratio for silent film, really, nobody knows why but probably because it makes a pleasing image, it's almost square and it's easy to work with.

The SLR/film 3:2 ratio does not come from the golden ratio, when the first roll film camera was made the only roll film available was movie film (4:3) they put the film sideways and used two movie frames for each still frame - two 4:3 frames on top of each other is 4:6 = 2:3

The "standard" aspect ratio closest to the golden ratio was 5:8, it was very unpopular because those proportions simply don't look good (yes, the golden ratio is not automatically the best ratio for everything, who would have guessed)

For everything about aspect ratios read the first answer to this question

  • and by now there are so many cheap sensors in the format that it would be foolish to use another and cause your company a massive investment, and your customers enormous frustration getting prints on a paper format that their printshop does not carry. – jwenting Jun 5 '13 at 11:48
  • @jwenting - I got into digital p&s photography pretty early, I remember the enormous frustration getting prints at 4:3 (and now that the standard default sizes shifted to 4:3 I've switched to a 3:2 DSLR) – Nir Jun 5 '13 at 12:04
  • oh yes, having to remember to always frame your shots so they'd leave some dead space at the edges that wouldn't hurt if the printer projected it outside the paper... – jwenting Jun 5 '13 at 12:16

The reason is historical. Before Micro Four-Thirds, there was Four-Thirds which defined a 4:3 aspect-ratio sensor. The reason is simply that Olympus research concluded that 4:3 aspect-ratio was most pleasing. They even had 4:3 half-frame (2X crop) film cameras.

When Olympus and Panasonic decided to go mirrrorless, it was advantageous to bootstrap the system by making it compatible with Four-Thirds but just changing the flange distance. This lets their cameras accept lenses via an adapter.

When Sony followed suit with their mirrorless, they kept the same 3:2 aspect-ratio as their SLT cameras which inherited the 3:2 aspect-ratio from their DSLR which they acquired from Konica-Minolta, who used - you guessed it - a 3:2 aspect-ratio.

Currently, there are 7 mirrorless manufacturers, 4 use 3:2 and 3 use 4:3 aspect-ratio. Almost every maker who had a legacy mount uses the same aspect-ratio in their mirrorless as they do in their DSLRs. The exception is Pentax which uses 4:3 for its Q-mount and 3:2 for its discontinued K-mount mirrorless. Fuji with no legacy of its own camera lenses, decided to go 3:2 which is used by all 1.5X crop cameras.

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