After taking a few days to read the initial reviews and hype for this new camera these would be the upsides over the E-M5 I see so far for U/W photography. First let me say that I think the E-M5 is an excellent underwater camera and that the Nauticam NA-EM5 housing is one of the best values in the market for a quality camera/housing package.
So what do I see as the up sides for making the switch to the E-M1. First the viewfinder is one of the best in the market bar none and with features you just can not get with an OVF. It has a viewing area larger than just about any DSLR on the market except for the $6800.00 Canon EOS-1D, it is even larger than the $6000.00 Nikon D-4 according to reports. It now has excellent AF speed for both M43 and 43 lenses and much improved C-AF speed. Build quality including weather sealing is even better than in the E-M5. The addition of a wider array of control buttons which are more spread apart and a built in guilty grip will make the camera easier to use both above and below water, i.e. I can better access the controls of the E-M5 inside the housing than I can above water. Higher speed flash sync and lower ISO both needed to get those black backgrounds in macro and for using wider F/stops above water. For Burhan if you can get 1/320th now with hard wired strobes this camera should give you 1/500th. The sweet new 12-40 F/2.8, I have used the Panasonic 12-35 and prefer it to the 12-50mm zoom this new lens should be even better and a real winner as my prime travel lens with minimum focus of about 7" across the full zoom range. With my first 43 and M43 cameras I never shot above ISO-400. With the E-M5 I have expanded to ISO-640 and if the reports are correct I should be able to shoot ISO-800 more more and be happy with the results. With the removal of the low pass filter and the new processing engine image quality improvement and sharpness have been reported. This is the first high end Olympus release I can remember where the body only option rather than the "kit" option is coming first so that those of us who already have lenses and can live without the 12-40 can have the camera at first release. I like the one touch white balance button on the front of the camera, I used it all the time starting with my E-1. Built in HDR and a host of other features will also interest many.
Who do I see buying this camera, I think we will see an even greater number of converts from the DSLR ranks to this camera which already has an excellent lens set for U/W photography. For those who are still using the LCD to compose and focus I don't expect to see a large exodus from E-M5. For those like me who religiously use the viewfinder I would expect along with the other improvements to see several many making the switch. If you are using the 45 or 180 add-on viewfinders this camera should be amazing. Focus peaking has been added for stills and along with the large viewfinder critical focus should be greatly improved. Along with the Olympus housing and based on the great success of the Nauticam E-M5 housing I would expect that Nauticam is taking a very hard look at this camera.
Phil Rudin