Nikon D3 Live View
Nikon D3 Live View Mode
Perhaps triggered by Olympus and Panasonic in the consumer SLR space, "Live View" on DSLRs is becoming more common as a feature. In the professional space, it's probably less driven by the convenience of framing on an LCD than it is by the need for a viewfinder display when the camera is operated remotely. (Although Live View features that provide for highly magnified displays can be a considerable help in checking depth of field and focus accuracy.)
We first saw a Live View mode on Canon's 1D Mark III model, where the mirror can be flipped up and a full-color image from the camera's CMOS sensor fed in real time to Canon's remote control software via USB, Ethernet or even WiFi. Canon's EOS-40D and 1Ds Mark III also both sport Live View modes, with a few enhancements beyond the capabilities of the 1D Mark III.
With the advent of its CMOS sensor (MOS sensors appear to be a requirement for Live View in DSLRs; data clocking off a large CCD is too inefficient and power-hungry), the Nikon D3 and D300 both now feature Live View modes of their own. Here again though, Nikon has gone the competition one better, by providing what's to our eyes the most useful and usable DSLR Live View mode yet.
What makes Nikon's Live View mode so uniquely effective are the two options it provides for autofocus operation. With the mirror raised and shutter open, the light path to the usual SLR phase-detect AF sensor is interrupted, so normal AF can't be used. As in the Canon 40D and 1Ds Mark III, the Nikon D3 and D300 address this problem via a focus mode that drops the mirror to determine focus, and then opens it again to restore the Live View display. All four cameras behave similarly in this mode of operation.
The real trick comes in Nikon's second Live View autofocus option. In this mode, the camera performs contrast-detect autofocus, just like any point & shoot digicam. That is, it simply reads data off the CMOS image sensor and evaluates how abruptly light to dark (or dark to light) transitions happen on the image plane. Contrast-detect AF isn't nearly as fast as phase-detect (this is why the shutter response of most digicams is so much slower than that of most DSLRs), but the camera can focus without interrupting the Live View display. As an added benefit, because it's working with data coming from the main image sensor, you can move the AF point anywhere you want within the frame area, right out to the extreme edges. You're also guaranteed that the selected focus point will be in focus: Because the focus determination is made with data from the main image sensor, there's no possibility of front- or back-focus, as could be encountered with conventional phase-detect AF systems.
In the screen shot to the right, the green rectangle shows the area being examined to determine focus. As noted, this area can be move to any part of the frame, right up against the top, bottom, left or right sides of the image area.
In all their discussion of it, Nikon has consistently emphasized that this mode was only for use with stationary objects, and with the camera on a tripod. Our lab testing of the D3's performance showed why Nikon takes this position: With most lenses, Live View mode stretches shutter lag to 1.5 seconds or beyond. If the lens has to slew a long ways from near to far or far to near, the lag time can be as long as several seconds.
This is another situation where a solution seems obvious once someone's mastered it. One has to wonder why Canon didn't provide a contrast-detect AF option as part of the Live View mode on EOS-40D and EOS-1Ds Mark III. (The original text here was written back in August of 2007. Since then, Canon has implemented contrast-detect AF in the EOS 50D, Rebel XSi and XS. Olympus has also implemented a contrast-detect AF mode on their E-series SLRs, but only with certain lenses, which have focus motors that are quick enough to give reasonable shutter lag results. Expect to see more cameras implementing contrast-detect AF in their Live View modes in the future.)
The D3 also provides up to a 13x display zoom in Live View mode, providing excellent focus discrimination when focusing manually. This is pretty key: Less than about 10x magnification really doesn't do the trick for getting the focus set right, but in playing with the camera at 13x, we felt we could pretty well nail the focus every time. What's particularly neat is that you can continue doing Contrast-Detect AF when you're zoomed: As you can see in the animation left, the green AF rectangle simply expands to cover the same area of the subject, and you can instantly confirm whether it's being successful or not.
With Live View mode comes the ability to control all aspects of the camera's functioning from a PC remotely, including focusing. Both the new Nikons and Canons include the ability to control the camera from a computer remotely, and that includes receiving a Live View image from the camera. You can focus, adjust settings, and fire, all from a computer. What's more, you can do it via cable or WiFi connection, with the optional WiFi adapters.
The new Nikons require optional Camera Control Pro software to enable this feature. Software for this feature is bundled with Canon cameras.