When fitting EF / EOS lenses to your MFT mount camera, you have a few options. Each option is priced differently and essentially tries to do the same thing, which of course means you can use your Canon glass on whatever MFT camera you own.
The three main types are as follows:
Basic adapter: $ 20- $ 50 +
Adapter with built-in aperture ring: $ 80- $ 200 +
Electronic adapter for controlling the lens aperture: $ 500- $ 700 +
All three adapters have their advantages and specific uses.
The cheaper base adapters are all you need when you want to take anything wide open. The more expensive adapters are all about controlling the iris of your electronically controlled Canon lenses, which is important to many people. However, if you have a very fast Canon EF lens and only ever use it wide open and in a pinch, buying one with aperture control may not be worth the extra investment. Personally, I know I have some lenses that I rarely, if ever, stop using. These are lenses that I own specifically for very low light situations. If you only have one or two lenses and only need them for wide-open use, a cheap base adapter is the way to go. If you own a Canon DSLR, one way to turn the lens off (although it's quite annoying) is to attach the lens to your Canon camera, adjust the aperture, and then put it on your adapter and MFT camera. This allows you to change the aperture on the lens. Every time you want to adjust them, you'll have to put them back on your Canon body to make the change.
The next stage is adapters, in whose adapters aperture blades are built. In essence, instead of actually stopping the aperture blades built into the lens, you can stop the iris through the adapter. This is a great option for those who mainly need to shoot relatively wide open, but may need to stop in some rare scenarios. The reason I am saying a few scenarios is that when these adapters shut down completely, they can often cause vignetting. This is because the aperture blades are in the adapter and not in the actual lens they are supposed to be in. However, this only seems to happen if you close the adapters completely and is not a problem with all lenses.
The top tier are the electronic adapters. These adapters essentially mimic what your Canon DSLR tells the lens to do. In terms of quality, you will get the best picture when completely turned off as you will not have any issues with vignetting as it controls the actual blades in the lens. If you own a lot of Canon lenses and are just switching to the MFT format, this option may be for you. While they are a bit expensive, this adapter will ultimately allow you to use any of your lenses in any scenario. However, if you don't typically shoot with the aperture wide open, it can be too much of a good thing for your needs. The other disadvantage of this type of adapter is that they require power. Either attached to the wall or some kind of battery rig. This makes working with the adapters on the fly a bit of a hassle, but is still a great option if you're working in a controlled studio environment.
When I decided on an adapter, I ended up in the middle and bought an adapter with manual aperture blades. The reason for this is that I don't have many Canon lenses and that I almost always shoot wide open with them. I didn't want to get any of the really cheap adapters because I want to quit in some scenarios and of course I wouldn't have had a chance with the cheaper adapters. I seldom or never stopped shooting, so any vignetting that can occur when it is completely closed is no problem for me. I considered the electronic option, but it just wasn't worth it for my use. I don't have enough Canon glass to justify this and I don't necessarily plan to include anything in the near future. I also don't like the idea of needing a power supply separately to use my lenses with. Although I mostly shoot in controlled environments, I just don't want this on-set hassle. It's one more thing to worry about for no reason as I can easily get away with not using it.
So I ordered the Fotodiox adapter from Amazon.com for $ 80. http://fotodioxpro.com/index.php/lens-mount-adapters/micro-4-3-mft-lens-adapters/fotodiox-pro-lens-mount-adapter-with-built-in-aperture-iris- canon-eos-ef-lens-non-ef-s-lens-to-micro-4-3-four-third-system-mft-camera-adapter-fits-olympus-pen-e-p1-pen-e- p2-pen-e-pl1-pl2-panas.html
I popped it on my Gh2 with my Canon 50mm 1.4 lens yesterday and was pretty impressed. The build quality of the adapter is by no means great, but it doesn't feel cheap either. It's what you would expect for the price. The iris ring is relatively smooth and there was no vignetting whatsoever with my 50mm lens – even when it was completely stopped. Ultimately, I was very happy that I didn't go for an electronic version like the RedRock adapter. It would just have been a waste to consider this as an option as this adapter completely covers my needs.
I've heard good things about the Kipon adapter listed above, and this one costs more than double the cost of the Fotodiox at around $ 180. I haven't used the Kipon myself but would assume you'll pay for the build quality. Compared to the Fotodiox, it may be a more robust, sentence-oriented device. I would also assume the aperture ring would work more smoothly. Although the ring on my adapter is sufficient for my needs, I would suspect that you will get a better result with the Kipon if you do a lot of iris scrolls while shooting and you need a buttery smooth ring with a smooth bezel.
Overall, I am very happy with the new adapter. It does what I need it for and does it well. It was a surprise that, unlike the product photo, my adapter has no aperture markings. It's simply numbered from 1 to 7 (as you can see in the photo below). I may have been sent an earlier version of the adapter. However, this is not a problem for me as the way I use this adapter does not require any specific bezel markings on the adapter. However, there is something to consider if you need this for your particular style of shooting.
UPDATE: If you are looking for an MFT adapter in the market, you have likely looked at both the GH3 and Blackmagic Cinema cameras. I recently did a quick and dirty comparison of the two cameras you can check out here