Overall impressions and Summary
The D90 and the 5D Mark II are pioneering products in this DSLR category.  Like most early products, they have design compromises and are far from perfect.  The buzz surrounding these two products tends to be highly polarized, with people either praising or bashing them.

The D90 is a lot of camera for the money.  It is not in the same league as the 5D Mark II, but is far less expensive.  And it has the advantage of being first in its category.  People have been playing with it longer, learning to exploit its potential, and how to either work around or work within its limitations, and what one might hope can be improved.  Nothing provides a quicker reality check to buzz and hype, than firsthand experience.

The EOS 5D Mark II is probably the most attention-getting new still-camera introduction of the past year, and for plenty of good reasons.  It pushes most of the edges of the envelope.  With a full-frame 35mm sensor, 21.1 megapixels, a high-ISO limit of 25600, and full 1920x1080p HD video at 30fps, its spec sheet is a list of superlatives.  Some very talented people have done astounding work with it even before it was released, using preproduction units.

Both Nikon and Canon have superb lens systems, and both DSLRs offer ample opportunity to exploit the special effects this makes possible.  Fisheye, super telephoto, wide-aperture, perspective control, selective focus, macro and micro – all are now as accessible to video as they have been to still photography.

The range of depth-of-field that is offered by the many fast lenses in these lineups is a particularly strong advantage that the larger-format sensors in the DSLRs have over the much smaller sensors in P&S cameras and many professional video camcorders.

The larger sensors in the DSLRs also allow for significantly better low-light performance than in their P&S or camcorder brethren.  This too is enhanced by the availability of fast lenses.

On the downside, neither DSLR offers much in the way of manual control while in video mode.  Those who have worked with preproduction units have either found ways to work around this (for example, using ND filters to force wide apertures) or work with it.

Also, the DSLR form factor is hardly ideal for video use.  Audio seems an afterthought.  There’s no good place to mount an external mike, something expected on high-end camcorders.  And the bodies are so small, there’s hardly room for all the controls needed for professional video work.  Volume controls, for instance.  On the 5D Mark II this can be worked around with an external audio adapter, but the complete lack of external audio input is probably a deal breaker for any professionals considering the D90.

Ergonomics are rather awkward with both DSLRs.  Unlike still-picture controls, their video controls do not fall naturally under the hands.  Video can only be captured in live-view mode, displayed on the main LCD panel.  The optical viewfinder is completely useless for video.  This can be a problem both from a power consumption standpoint (those big displays are power hogs) and on bright outdoor shoots where the LCD displays might be hard to read.  Holding the camera at arm’s length to view the LCD is fatiguing.  Frankly, both Nikon and Canon recommend the use of a tripod for video, advice which is probably best followed (or at least use a shoulder brace or torso pod to take the weight of the camera off the arms).

The DSLRs also come up short on focus and zoom controls.  What, you say – don’t DSLR lenses have focus and zoom rings?  Yes.  But still cameras focus and zoom between pictures, not during them.  They do not have provisions for smooth, steady zoom, with ramped start and stop speeds – another norm expected on good video cameras.  Or focus stops that limit focus travel between a foreground and background object, helpful when using shallow-DOF selective focus as a narrative element in video.  These things can still be done by a skillful operator, just without much assistance from the hardware.

Perhaps the most troublesome limitation of the current crop of DSLRs is the “rolling shutter” video effects caused by their use of CMOS rather than CCD sensors.  These effects are quite visible on sample footage taken by the Nikon D90, and can also be seen on the Canon EOS 5D Mark II samples if you know where to look.  These artifacts limit the cameras’ usefulness for whole genres of videography – sports action for instance.  They are not show stoppers, just another stumbling block to watch out for.

Most professional camcorders, and many of the small P&S cameras, use CCD sensors, and so don’t show these rolling-shutter artifacts.  Most DSLR still cameras use CMOS sensors, which are great for still pictures, but problematic for video.  It will be interesting to see if and how this is solved.  Adding storage cells to CMOS sensors? [Unlikely due to cost and noise tradeoffs.]  Offering versions with CCD sensors?  {Perhaps more feasible, though it would impact power consumption.]

Nikon, with massive experience in photography but little in the video market, has entered it albeit through the backdoor, with the D90.  As might be expected, they stumbled a little, especially on the audio and motion-capture specs.  One could say, though, that they’ve otherwise done nicely for a first offering, especially at the price offered.

Canon, with plenty of experience in marketing both still and video products, has positioned the EOS 5D Mark II as a crossover product, appealing to photographers and videographers alike.  It is not quite the ultimate do-everything product they might want to sell, but it still offers an amazing synergy of capabilities.  In its current form it’s a far better still camera than video camera.  But it does plug gaps in the indie videographer’s armament.  It will be fascinating to see what they do with the next iteration of this product, or whether they introduce video capability into their other high-end DSLRs.

Panasonic has video credentials to match Canon’s, though perhaps not the same street cred in still cameras.  The rumored Lumix G HD looks like a low-end offering, but it will be fun to see if they follow it up with something more substantial.

And then there’s RED Cinema, with their DSMC line.  Most of this stuff is in a totally different league than the other products in this survey, though the Scarlet 3K is priced about the same as an EOS 5D Mark II.  RED comes to the still market from video, so they’ll have a tough sell establishing a reputation on the new turf.  However, they’ve proven themselves as a supplier of high-performance video gear with aggressive price points.  They may well be able to carve out a niche in the high end of the video/still hybrid market, once their Scarlet and Epic products become hardware rather than vaporware.

I could not sum up the current state of affairs any better than did Vincent LaForet, so I will just quote him from an interview about his experience in making the short film “Reverie” one intense weekend in New York City with a borrowed prototype of a Canon EOS 5D Mark II:

“Remember, it’s a first generation technology.  If people are expecting it to perform at the same level as a professional video camera, that’s kind of a compliment.  People are ready to use it for projects it was never really meant to do at this point.  That speaks to how advanced this camera is for its time.”