Sunday, 26 January 2014

Put APS-C sensors in Micro Four Thirds cameras

By far the most common sensor size for system cameras is APS-C. As the name suggests, the size is derived from the Advanced Photo Systems, a still image film format introduced in 1996. Almost all mirrorless camera systems use APS-C, with the exception of Nikon 1, Pentax Q, and Micro Four Thirds. There is also the Sony A7 with a full frame sensor, but it still has a very small volume.

On top of this, all consumer DSLR cameras use the APS-C format. Again, there are some exceptions: Some full frame cameras that sell in smaller volumes.

While never officially confirmed, there is a strong belief that all recent Olympus M4/3 cameras use sensors from Sony. They are: E-M5, E-PM2, E-PL5,E-P5, and E-M1. In addition, the Panasonic GH3 is said to use the same sensor.

The imaging sensor is one of the most expensive items in a digital camera. And the cost is strongly correlated with the sensor size. Hence, some have speculated that the choice to use a sub-APS-C sensor size in Four Thirds and Micro Four Thirds cameras is more related to economy than an evaluation of what the optimal size is: With a sensor that is approx 40% smaller, Micro Four Thirds cameras can be sold at a larger margin, compared with APS-C cameras.

However, there is more to the cost of production: There is also economics of scale. As Sony is producing a massive number of APS-C sensors, I suggest to use this sensor size also in Micro Four Thirds. That would probably cost pretty much the same as a 4/3 size sensor, given that they don't need to support one more sensor size.



Most Micro Four Thirds lenses don't have an image circle large enough for APS-C. Here is one illustration, taken with the Sony NEX-3N using a a M4/3 to E-mount adapter and the Lumix G 14-42mm f/3.5-5.6 at 18mm f/10:


Using a Micro Four Thirds lens on a Sony NEX camera is possible, since the Sony E-mount has a shorter register distance than M4/3. The difference is about 2mm, so a thin adapter is possible. However, the adapter does not transmit electric signals, and there is no control over aperture and focus at all.

As you can see from the example image, the lens covers little more than the Four Thirds sensor. Also note that there is some barrel distortion. This is because there is no geometric distortion correction done when using the lens on a non-Micro Four Thirds camera.

But as most Micro Four Thirds lenses cannot render the whole APS-C sensor, why do I suggest to use them in Micro Four Thirds cameras? The reason is to achieve a multi aspect sensor.

The Panasonic GH1 and GH2 came with the oversized multi aspect sensor. However, when the GH3 was released without the feature, it did create some disappointment. The reason for dropping this feature from the GH line of cameras was probably cost: It didn't make sense to produce yet one more sensor size for the sake of one single low volume camera model.

Using an APS-C sensor and cropping it for the Four Thirds image circle, though, they could easily achieve the multi aspect sensor feature. This would be done by using the lens image circle more efficiently in the 3:2, 16:9 and 1:1 formats, as illustrated:


This would achieve using the image circle more efficiently, getting the same diagonal field of view in all the modes 1:1, 4:3, 3:2 and 16:9, and getting more megapixels in all modes. Except for 4:3, which remains the same, of course. In this setup, the APS-C sensor would always be cropped, and the extreme right and left parts of the sensor would never be used.

Regarding the number of megapixels, the APS-C sensors come in many variants. Most Sony NEX cameras have 16MP, and cropping a Four Thirds sensor size from this one would yield 10MP, probably too little for today's market. However, using an APS-C sensor with 24MP, for example the one used in Sony SLT 65, would give 15MP in 4/3 crop mode, which I think is an ok image size. The added benefit of getting better resolution in non-native aspect ratios would certainly make up for it.

When making the example image above, I went through a lot of Micro Four Thirds lenses trying to find the one with the smallest image circle. And I was surprised to find that many had an image circle filling out almost all of the APS-C sensor in the Sony NEX-3N. Here is the Olympus 45mm f/1.8:



And the Lumix G 20mm f/1.7:



As you see, these images are just a little bit dark in the corners. After adjusting for geometric distortion correction, the image from the Lumix G 20mm lens would become almost free of vignetting. So, if you had a Micro Four Thirds camera with an APS-C sensor, many of your lenses could be usable at a wider crop.

However, my suggestion is to use APS-C sensors mainly to enable the multi aspect ratios, not to use a larger image circle than 4:3. However, that could be an added bonus. If a M4/3 camera with an APS-C sensor would be able to give you a 30% wider horizontal field of view with lenses like the Lumix G 14mm f/2.5, wouldn't a lot of people be interested, even if it costs more? I think so.

Putting APS-C sensors in Micro Four Thirds sensors would allow the manufacturers to consolidate the number of sensor sizes. This is good for keeping the costs down. And as Olympus and Sony are now cooperating, why keep producing both Four Thirds and APS-C sensors?

22 comments:

  1. You are trying to catch two birds with one stone: (1) "Using an APS-C sensor and cropping it for the Four Thirds image circle, though, they could easily achieve the multi aspect sensor feature." & (2) "Putting APS-C sensors in Micro Four Thirds sensors would allow the manufacturers to consolidate the number of sensor sizes. This is good for keeping the costs down."

    Are these two goals reconcilable? You yourself said m4/3 would need at least 24MP APS-C sensor to have enough resolution. Are 24MP APS-C sensors cheaper than 16MP m4/3 sensors?

    ReplyDelete
    Replies
    1. I don't know which are less expensive. But I am sure a lot of managers at Sony and Olympus would like to simplify their product portfolio.

      Delete
  2. You need to consider the extra power costs of that added and unused silicon.

    ReplyDelete
  3. This is actually a very well thought out idea, in my opinion. Especially given how well the M4/3 lenses seem to cover the APS-C sensor, it seems like a very neat solution indeed. You may well end up with higher rather than lower resolution images if you can use most of a 24MP APS-C sensor (a la NEX-7).

    ReplyDelete
  4. Would this have any low-light benefits? To me, that is the last major hurdle for M43 and my new GH3 is leagues above my GF1 at light sensitivity. Great article!

    ReplyDelete
    Replies
    1. I don't think you would see any low light benefits from this approach. Most crop sensors today are rather similar in low light performance.

      Delete
  5. Very nice thoughts. But how about the mount size? I don`t think the m43 mount size gave enough space for APS-C sensor.

    ReplyDelete
    Replies
    1. The picture taken with the Olympus 45mm lens on the Sony NEX-3N in the article above answers your question. The lens has an M4/3 mount, but still the image from the lens fills the whole APS-C sensor surface. So this is not a problem.

      Delete
    2. Thank you for your reply. I mean the sensor space in the camera body, just inside the mounting ring in the body. Because there are connector pins. And the edge of the 43 sensor is almost meet the body mounting ring. I hope you can understand what I mean. But I think the idea of using bigger sensor size to keep the FOV in every aspect ratio is great.

      Delete
    3. When I put the adapter on the Sony NEX camera, it becomes like an M4/3 camera, but with an APS-C sensor. Still, the Olympus 45mm lens fills out the entire sensor, so this shouldn't be a problem.

      I can see your point, that adding electrical contacts inside the mount is going to take up a bit more space. However, I don't think that should make any difference here.

      Delete
  6. I love m4/3 OM D because it handles like my thread mount Leica IIIG and gives me superb through the lens viewing like my Nikon F. I never thought i'd live to see the best of both worlds. So long as I have two OEMs competing to produce high quality lenses they can give me a more versatile sensor in my next body, particularly if it keeps both Panasonic and Olympus viable. I can see little downside to this possibility if it is workable from the manufacturer's viewpoint Again an excellent thought provoking article.

    ReplyDelete
  7. I had a similar idea which is that they should make the sensors circular so it doesn't matter which way you hold the camera. A circular image file would give great flexibility in terms of aspect ratio after you take the shot. I also think this is a bit more efficient in terms of the sensor area because when using an over-sized rectangular sensor there are some bits in the corners that will probably never get used (if they are used it will be distorted anyway). I like to crop after shooting and I think your suggestion or something similar would be a major selling point.

    ReplyDelete
    Replies
    1. I'm not sure, but I think producing a circular sensor would be more expensive than an oversized rectangular one. So if you had an APS-C sized sensor in a M4/3 camera, you would be able to rotate it a fair amount without losing any resolution, given that you are only after the contents inside the 4/3 image circle.

      I also crop and rotate images quite often, and I would certainly like to have a larger image to crop from.

      Delete
  8. I hope, no, I know that better sensors and image processors are coming. I expect to see a leap forward in image quality in one of two years. It would be nice to have better dynamic range and one of perhaps two stops better high ISO performance.

    ReplyDelete
    Replies
    1. My idea exactly. I have an E-M1 and three primes. That's enough for most of my photography needs. Great ergonomics and decent image quality. I happen to like the 4:3 aspect ratio very much. I never liked the old 3:2 standard. It's handy to have the option though. I say, use what you got and upgrade when you need to. I know too that a new sensor will come. I can only hope that olympus chooses better performance over more megapixels. My Sony a6000 doesn't give anything more than my E-M1. 24 megapixels is not a necessity.

      Delete
  9. I have sony a6000 (apsc sensor) and planning to buy Olympus M.Zuiko Digital ED 12-40mm f2.8 PRO, is that ok? what are the pros and cons? Any available adapter in the market? Thanks

    ReplyDelete
    Replies
    1. I would strongly advice against doing so. Using the adapter described here, you can mount the lens to the camera. However, you will not be able to operate the aperture or the autofocus, so the lens is hard to use. It is easier to use lenses from Sony.

      Delete
    2. In theory, the 12-40 Pro should work well, as it has a clutch mechanism that allows for a mechanical focus. It's very sharp at 2.8, too. I intend to see how it works on my A7II (yes, I know...), when I can find a supplier that can confirm their adapter will fit the modified E Mount of mine and the A7RII.

      Delete
  10. This is a good, thought-provoking article.

    However, you forgot to mention one advantage of using a larger sensor, which is that you can shoot portrait-orientation without having to hold the camera at 90 degrees.

    The example images that you've given above all crop away the top and bottom of the image circle / sensor, which could be used for multi-aspect portrait shooting.

    ReplyDelete
  11. Plenty on ebay. http://www.ebay.com/sch/i.html?_nkw=micro+4%2F3+to+nex+adapter
    micro 4/3 to e-mount chinese adapters.

    Looks like fun. I might get one and see if they suck or not. Since I like the square aspect ratio micro 4/3 would be no loss anticipating a crop. Framing might not involve guesswork, though. At first.

    * Automatic diaphragm, auto-focusing,or any other functions will not operate correctly while using this adapter.
    ** "Stop-down mode" will need to be used when metering since the lens does not have the ability to have its aperture controlled by the camera body.
    *** Focusing infinity.

    ReplyDelete
  12. That's an idea I like! I think if we ever see this, we'll see this in mobile phones. That would introduce the idea to the public and make it easier for m43 manufacturers to take the risk.

    ReplyDelete