So the E-M1 should finally be announced on Tuesday (or late Monday, depending where you are in the world). Most of us are coming at the E-M1 from the perspective of current m4/3 users, be it as E-M5, Pen or Lumix G users. But from what we know right now, Olympus is trying to position the E-M1 as the successor to the professional E-series of DSLRs. While we can quibble about how much of an upgrade it will be over current m4/3 models, considered in the context of the E-5, E-3 and E-1, I think the E-M1 actually looks quite remarkable, keeping in mind when those camera were released. Particularly vs. the E-5. E-M1 vs. E-5 (released in September 2010) Sensor: 16MP Sony NMOS vs. 12MP Panasonic NMOS. Among other things this means major improvements in noise at all ISOs even above and beyond the E-M5. It's more than a stop better than the E-5 in that regard and the dynamic range (as judged by the E-M5) is quite a bit better too, in both the highlights and the shadows. The Sony sensor also does away with banding at ISOs < 6400. Less significant but still nice is the 33% increase in overall resolution and the removal of the anti-alias filter. Body Image stabilization: 5-axis vs. 2-axis . The E-5's stabilization was a bit better than the one found in the Pens. The newer system is at least a stop better. Autofocus: debatable. This is probably the biggest question mark. How well will the E-M1 focus 4/3 lenses. And how well will C-AF work, both with 4/3 lenses and m4/3 ones. Some reviewers peg S-AF performance behind the E-5, others suggest it's as good or better. The same is true for C-AF. Framerate: 10/6.5 fps vs 5 fps. We don't know what the future holds for C-AF, but in terms of frame-rate this will be a huge jump without tracking (10 fps) and a decent increase with (6.5 fps). Viewfinder: 100% 1.48x 2.4MP EVF vs 100% 1.15x OVF. Probably the most hotly debated change by the 4/3 faithful. The EVF is now clearly bigger, and the OVF obviously has no lag. Screen: 3" 1040k tilting touch-sensitive LCD vs. 3" 920k fully-articulating LCD. The E-M1 drops the fully-articulating LCD in favor of the E-M5's tilting one, but adds touch-control. Video: 1080p30/24 AVCHD vs. 720p30 MJPEG. While Olympus is clearly lagging Panasonic on video, this is still a substantial improvement. Size/weight: ~130x94x63mm/500g vs. 143x117x75mm/895g. The E-M1 looks a bit smaller and lighter than the Panasonic GH3, which is to say the same size as Canon and Nikon's smaller DSLRs, the D3200 and Rebel T3. The E-5 on the other hand is slightly smaller and just as heavy as a professional full-frame DSLR (e.g. Nikon's D800 and Canon's 5Dmk3. Lenses: m4/3 + 4/3 vs. 4/3. The E-M1 essentially more than doubles the selection of fully-functional (S-AF/C-AF, auto-diaphragm) lenses available, as compared to the E-5. MSRP: $1700 vs. $1400. $300 drop in list price, although 4/3 users will need an adapter for their existing lenses, which at least for now is free with rebate. Compare these changes to what the E-5 offered vs. the E-3 (released in October 2007) Sensor: 12MP Panasonic NMOS vs. 10MP Panasonic NMOS. A lighter AA filter significantly increased detail (more so than the 20% increase in resolution). High ISO noise improved a bit and banding was significantly reduced below ISO 1600. On the downside, low and mid-ISO noise actually increased a fair amount due to Olympus's new approach to DR (underexpose and push in processing). Body Image stabilization: no change. Same 2-axis system, with same claim of 'up to 3-stops' of stabilization. Autofocus: various improvements. Speed improved in low light, accuracy in most situations, C-AF saw some improvements and the addition of AF tune made it possible for E-5 users to compensate for repeatable AF errors on their lenses. Framerate: no change. 5 fps on both. The E-5 had a slightly smaller RAW buffer (20 vs 23 frames). Viewfinder: no change. Same 100% 1.15X OVF. Screen: 920k fully-articulating LCD vs. 230k fully-articulating LCD. Screen resolution on the E-5 was drastically improved over the E-3. Video: 720p30 MJPEG vs. nothing. The E-3 didn't have video. Size/weight: no change. Externally the bodies appeared virtually identical. Lenses: same. The E-5 did have slightly more native lens models available at the time of release due to various Olympus releases, but at the same time Sigma discontinued many of their 4/3 mount lenses. MSRP: $1700 vs $1700. No change. Finally, the E-3 vs the E-1 (released in June 2003) Sensor: 10MP Panasonic NMOS vs. 5MP Kodak CCD. The E-3 dramatically increased real resolution. High ISO noise decreased by around a stop, but the Panasonic sensor did exhibit banding starting as low as ISO 400, something the Kodak sensor avoided. Shadow dynamic range improved slightly, whereas highlight dynamic range dropped. Body Image stabilization: 2-axis vs. none. The E-1 did not feature image stabilization. Video: none (no change). Autofocus: faster 11 cross point vs. more reliable 3 point system. In good light, the E-3 was far faster. In poor light, it was sometimes faster and sometimes failed to lock entirely. There were also wide-spread issues with AF accuracy on the E-3, whereas the E-1 had no notable reports of front- or back-focus. The E-3 offered improved C-AF, although it was still far from dependable, even compared to its contemporaries. Framerate: 3 fps vs. 5 fps. Not only was the E-3 faster, but it had a much larger RAW buffer for continuous shooting (23 shots compared to just 12). Viewfinder: 100% 1.0x OVF vs. 100% 1.15x. The E-3's OVF was noticeably larger than the E-1's. Screen: 130k 1.8" fixed LCD vs. 230k fully-articulating LCD. The E-3's articulating LCD was the first in a camera of its class. The E-3's addition of Live View made that addition particularly helpful. Video: no change. None. Size/weight: 141x104x81mm/660g vs. 142x116x75mm/895g. Although size was pretty close, the design of the grip on the E-3 made it seem larger to many folks. It also added 30% in terms of weight. Lenses: same. It's easy to forget that Olympus (and Panasonic and Sigma) built the 4/3 system from scratch in the roughly 4 years between the E-1 and E-3. The E-1 was released alongside 4 lens models. By the time the E-3 came out, there were more than 2 dozen. MSRP: $2200 vs. $1700. Olympus had a hard time selling E-1s early on before they dropped prices, and chose to adjust accordingly for the E-3.