Sans Mirror — mirrorless, interchangeable lens cameras  

Each system has its own strengths and weaknesses:

Nikon 1

• Strengths: video, sensor, autofocus performance, F-mount compatibility (with adapter), novice user orientation
• Weaknesses: lens choice, low-light performance, overall size versus sensor performance, high-end user control, range of available models, 2.7x crop sensor size

Micro 4/3

• Strengths: video (Panasonic), autofocus performance, lens choice, range of available models
• Weaknesses: sensor performance, low-light performance

Ricoh GXR

• Strengths: photographer-centric body design, modularity, Leica M-mount compatibility, APS sensor size
• Weaknesses: cost of lensors (sensor+lens modules), lensor choices, lack of dealers, video capability

Samsung NX

• Strengths: photographer-centric designs, APS sensor size
• Weaknesses: sensor performance, lens choice (though improving)  

Sony NEX

• Strengths: APS sensor size, sensor quality, low-light performance, Alpha mount compatibility (with adapter), user control (NEX 7)
• Weaknesses: size of lenses, user control (NEX 3, 5), lens choice (improving slowly), tendency towards overheating

As with DSLRs, there are advantages to staying within an ecosystem (Nikon, Olympus, Sony, etc.). In particular, the Nikon 1 and Sony NEX models have very good compatibility with their DSLR lenses via adapter (4/3 adapted to m4/3 tends to have poorer autofocus performance). So if you own a DSLR from a brand, the first place you should look is at the mirrorless camera from the same brand. Only if there's something that doesn't suffice in that mirrorless camera (the lack of user control on the Nikon 1 models, for example) should you look at out-of-brand solutions, in my opinion. 

That said, I've been basically two-brand since the beginning of mirrorless: I have full Nikon F-mount systems (both FX and DX) and m4/3 mirrorless systems. One reason for this was that m4/3 was the first truly smaller system for which I was able to build a near duplicate lens set. For example: my Nikon 14-24mm on FX is matched by Panasonic 7-14mm on m4/3. Yes, I don't have aperture equivalence, but it does allow me to stay shooting with the same approach with both m4/3 and FX in my landscape work. If, for example, I'm mostly shooting in front country, carrying a heavy, bulky D3x and 14-24mm lens aren't really a burden. However, when I go seriously into the back-country, having an E-P3 with the 7-14mm allows me to capture many of the same images while carrying a far smaller and lighter kit. When you're trying to hike 16 miles on tough trails in a day, the size/weight difference is indeed something that is meaningful.

Bottom line, there's no easy answer to this question. You have to evaluate your needs and wants carefully against what's available and pick the system that works best for you.

Here my answer is going to be a little different. The Panasonic GH-2 is arguably the best of the bunch. Beyond having manual controls while shooting video, it has a host of other features and abilities that make it the best suited mirrorless camera for video work, in my opinion. If you're the adventurous sort, you can even "hack" the GH-2 firmware to provide higher quality video (less compression) than it does out of the box. On top of all that, the GH-2 is the only still camera I know of that has an "all pixels" video mode. This special feature grabs 1920x1080 pixels without sub-sampling directly from the center of the frame (which means it's a crop of the entire sensor) and produces some of the best quality telephoto video work I've seen out of anything short of very expensive pro gear. 

The Nikon 1 and Sony NEX are no slouches for video, either. The Nikon 1 has quite good color, better than many dedicated video cameras, plus it has manual video control (despite being a mostly automatic camera otherwise). The Sony NEX 5 and NEX 5n models have very good low-light capability for video work. Coupled with the 16mm f/2.8 you can stick these small cameras into very small spaces where you wouldn't ordinarily be able to do video from.

Most of the rest of the cameras I write about on this site do adequate video for most purposes, but none really stand out as do the ones I just wrote about.

Vitaliy Kiselev managed to dissect the GH-2 (and GH-1 for that matter) firmware and figure out how to use it to have the camera's built-in ASIC use different settings than are revealed through the usual menu system. You can find out more about his firmware hack here. Currently, some people are getting 176Mbps streams out of the GH-2 successfully. That compares with the more usual 25Mbps rendered by conventional AVCHD compression cameras like the GH-2 typically max out at. More bits per second means less compression is going on, which has impacts on the clarity of motion and rendering of fine detail.

So why didn't Panasonic just do this themselves? First, AVCHD is a standard centered around Blu-Ray discs. The implication is that Panasonic picked something that they can guarantee that you can record to Blu-Ray. Given that's about the highest density recording medium accessible to most people, the decision makes some sense. But beyond that, as you kick up the bitstream issues of tolerances start to come up. The card you have might not actually support that much data coming at it, for example. Thus, I suspect that Panasonic simply picked some reasonable and conservative settings for the compression engine that would guarantee no dropped bits/frames/data. 

If you try the hack, do plenty of testing of the exact settings you're going to use before relying upon it. Make sure that your camera and card are compatible with the settings you choose, and test the compressed stream with your video editor. On the flip side, if you're deep into video and have a GH-2, there's almost no down side to trying the hack (as long as you pay really close attention to the instructions) as I've seen almost everyone be able to find settings that record better quality video (less compressed data) from their camera/card combination.  

Yes, it is quite exposed on most of these cameras. The biggest danger is changing lenses in wet conditions (mist, light rain, etc.), where if any of that moisture gets directly to the sensor you're likely to end up with either smears (if you try to wipe it off) or bubbles (if you let it dry) in your photos. So be careful on rainy days, around waterfalls, near the ocean, and other places where there's real water droplets in the air. I'd also point out that pollens can be a problem too, so if you're in the middle of a big pollen proliferation, be careful, too. 

Sorry to say, but yes, you will eventually need to clean the sensor manually. Some cameras are better than the others shaking off the light stuff (Olympus seems especially good), but those shake-it-off dust removal systems can't deal with moisture, pollens, sticky particles, and eventually, the cumulative dust build-up. If you want to see what your camera is shooting through, set f/22 and take a picture of plain blue sky. You might be surprised at what you find if you've been using your camera for a long, long time. 

"But I don't shoot at really small apertures so I don't normally see that stuff in my images" you might say. True. But if it's there, it's slowly building a contrast-removal filter over the sensor. It might not be a lot of contrast, but if you value getting the best possible pixel data from your shooting, I'd encourage you to test your camera from time to time and have it cleaned if you find a great deal of dust build-up.

I've got a cleaning the sensor article on my other site, if you're interested in what's involved.

Yes, there are differences in approaches between the two companies, even though they often use the same sensor and create cameras that look similar (e.g. GF-3 and E-PM1). 

Panasonic requires lenses to have image stabilization; they do not include it in their bodies. Panasonic tends towards more video capability, especially in a few models such as the GH-2 (and the GH-1 and GH-2 have been hacked to add even more capability). Panasonic has models with built-in EVF (e.g. G3, GH-2). Panasonic has models with higher megapixel counts (up to 18mp at the moment). Panasonic has the only models with fully swivel LCDs (e.g. G3, GH-3). Panasonic has several models with touchscreen interfaces. Panasonic JPEG rendering has improved in recent models, but still lags state-of-the-art. In the US, Panasonic has been abysmal at delivering product quickly, and has minimal dealer support.

Olympus uses in-body image stabilization, thus can stabilize any lens. Olympus' video capabilities tend towards automatic and fewer feature choices. Olympus supports off-camera flash in some of their models. Olympus has external EVF for most of their cameras, though those EVF models are not as good as the Panasonic internal versions. Olympus only makes one model with a tilt LCD (E-PL3). Olympus JPEGs tend to appeal to users more (more contrast, better color, better noise/sharpening choices).

In the beginning, Olympus had more compact lenses than Panasonic, though that is now starting to even out, and, of course, you can use an Olympus lens on a Panasonic and vice versa.

There really isn't a bad choice between the two, only a lot of small differences. I'm a firm believer that how comfortable you feel with a camera will be a large factor in how good the results you get of it are, thus I strongly encourage you to try both and pick based upon that if there is no single other factor that tilts the choice. For example, if you like eye-level shooting, the Panasonic G3 is a more comfortable camera than the Olympus E-P3 with the external EVF. 

First things first: I've gotten many great images out of my m4/3 cameras and continue to use them. Used correctly, an m4/3 camera can deliver excellent images. However, in terms of the deep underlying capabilities of the sensor, the Panasonic sensors are lagging--they have attributes that are similar to sensors a generation or more old and aren't exactly where the should be in the mirrorless competition. For example:

Quantum efficiency

• Nikon 1: 57%
• Olympus E-P3: 41%
• Sony C3: 45%

Minimum Read Noise

• Nikon 1: 6.8e
• Olympus E-P3: 8.1e
• Sony C3: 3.3e

Maximum Electron Capacity (Saturation)

• Nikon 1: 23,644e
• Olympus E-P3: 17,791e
• Sony C3: 21,361e

What this means at the lowest levels of how the sensors work is that the smaller Nikon sensor is performing in ways that the larger Panasonic sensor can't match. That doesn't mean that the Nikon 1 images are better than the Olympus E-P3 images, but it does mean that the smaller camera performs far closer to the larger camera than one would expect. Indeed, the current m4/3 sensors are closer to the smaller Nikon 1 sensors in some underlying performance values than they are to the larger Sony APS sensors. 

Time will likely correct such anomalies and even things out so that the sensor performances better match that implied by their size. But as I write this, the Panasonic sensors seem to be lagging in key parameters.

For both Olympus and Panasonic the answer is Panasonic. At least four different variations of sensor design exist already, but most of the models all share the same basic 12mp Panasonic sensor.

m4/3 is mirrorless, while 4/3 is not. The (mostly) older 4/3 cameras were designed as DSLRs, complete with mirror box and optical viewfinders. Because of the mirror, the lens mount on the 4/3 cameras is far forward from the sensor. On m4/3 cameras, the lens mount is very near the sensor. Thus, while m4/3 and 4/3 share the same sensor size, they do not share the same lenses.

They are manufactured by Aptina for Nikon, using Nikon designs. If you're surprised by this answer you shouldn't be: Nikon has had sensor design teams going back to at least 1988. Those teams have produced five Nikon-only sensors and have worked with at least two other partners on others.

Well, consider the differences:

• J1 no EVF, V1 has an EVF 
• J1 has less rear LCD resolution (460k dot versus 921k dot)
• J1 has only an electronic shutter, with a slow 1/60 flash sync speed, the V1 adds a mechanical shutter option with a 1/250 flash sync speed
• J1 has a slightly smaller body with no protrusion, the V1 has a protrusion for the EVF
• J1 has no accessory port, the V1 does (supports flash, GPS, more)
• J1 has a internal flash, the V1 doesn't
• J1 has a smaller buffer (18-19 NEFs at 5 fps) than V1 (44-45 NEFs at 5 fps)
• J1 has only internal mics for video, the V1 supports an external microphone
• J1 doesn't have a dust reduction system, the V1 does
• J1 has a 230 shot battery life, the V1 a 400 shot battery life
• J1 uses a new battery (EN-EL20), the V1 uses an existing battery (EN-EL15)
• J1 has an aluminum body, V1 has an aluminum magnesium body
• J1 doesn't have regular audio visual output, V1 does; both have HDMI output, though
• The J1 is less expensive
• The J1 comes in black, white, red, pink, and sliver, the V1 comes in only black and white

So, if one of those things is important to you, it should dictate which camera you buy. For a less expensive not-quite-pocket camera that isn't going to be accessorized, the J1 is probably the answer. For the serious shooter who wants complete flexibility in accessories, the V1 is the answer.

Samsung. Samsung is one of the biggest sensor makers in the world, though mostly in smaller sensors for phones, computers, and security systems.

Sony. Sony Semiconductor has a long history of sensor development, and the NEX sensors are simply the latest iteration of a long chain of APS-sized sensors they've made.

In long periods of recording video, yes, in my experience (NEX 5, NEX 5N) you'll eventually push them into heat shutdown. For still use, I've not triggered a heat shutdown, though I believe it to be possible (perhaps in extremely hot weather with very frequent shooting). With "regular" shooting, I don't deem this to be a huge issue worth worrying about. However, do note that heat causes electron migration within a sensor and thus increases noise tendencies. 

The simple answer is: remove the air. That's one nice thing about the mirrorless cameras, they are small and many can fit into the kinds of zipper lock bags you might have in your kitchen. Ditto for lenses. It's the air that's holding or producing the moisture as you move between inside and outside where there are extreme temperature and/or humidity differences. Thus, reducing the amount of air around the camera or lens helps considerably. (1) Bag the camera or lens. (2) Remove as much air from the bag as you can and seal the bag. (3) Give the camera or lens some time to adjust to the new environment before opening the bag and using them. Some people also add a small silica gel (water absorption) pack to their bags. There's no perfect solution for extreme environment changes, but this simple procedure helps a lot. Also, if you have control over your indoor environment, then adjusting your humidity and temperature to be less extreme compared to the outdoors helps, too. One other thing: automobiles retain humidity (or reduce it with air conditioning), too, so treat the inside of an automobile the same way you do the inside of a house. 

This question has come up a lot recently because people fear that the Olympus camera business will be shut down or acquired. The company is most certainly under huge stress now, and the entire board (which includes many members of the executive team) is implicated in what's happened. After restating their financial numbers for the past five years, undergoing an external audit (though by people appointed by Olympus), and generally admitting to what happened, the actual fraud is mostly behind them. The issue now is clean up. We're likely to see investment in Olympus by another Japanese company and/or banks to shore up finances and give them some operational breathing room.

The worry when you buy into a system is that the system won't be around forever, thus upgrade and updating options will go away. Unfortunately, the risk of that isn't zero for any system. The scandal increased that risk for Olympus aficionados, but probably only minimally. Plus, Panasonic shares the m4/3 mount, so you could always just replace your Olympus bodies with Panasonic. So while there's risk, I judge it to be a very low risk overall.   

You're probably on a Macintosh. Fujifilm apparently still doesn't understand that Apple uses a different file structure than Windows (what's it been now, 26 years?). When you download a file using a Mac or iOS device such as the iPad, there's potential for the computer or device to "touch" the filesystem and write information there. Spotlight (Apple's search system) is notorious for this, but there are plenty of different programs and services that can add files on mounted storage (true of Windows, too, but generally the file structure is different and understood by the Fujifilm firmware). 

Short answer: lock your card before mounting it on an Apple-based system, and then nothing will ever get written to it that the X-Pro1's firmware will have trouble understanding.  

The interesting thing is that the X-Pro1 tries to read NTFS files, but fails and then just decides to go about it's own business. No error message, no shutdown, just a long delay while it tries to parse a file it doesn't understand and then gives up. 

Bottom line: this is a Fujifilm problem and needs to be addressed in updated firmware. They'll say that it's an Apple problem because technically Apple doesn't follow DCF. But why should they? DCF was an attempt by the Japanese camera companies to force a standard for camera media, but they also were trying to force it on pre-existing operating systems that had moved from the old 8.3 FAT-based definitions. The reason you can type a long file name in OS-X and Windows is because those operating systems had evolved. They can also deal with larger files and more of them than DCF. The reason why Windows supports DCF slightly better is that Windows has the legacy of 8.3 FAT inherited from MS-DOS, and Microsoft has chosen to continue to support that legacy.