Nikon D90 Video

The Nikon D90's video capabilities are unusual enough (the first SLR to offer video recording) that we felt they deserved a page of their own, to cover them.

Resolution & Recording Time
The Nikon D90's movie resolutions include 1280x720 (16:9), 640x424 (3:2), and 320x216 (3:2). Recording times are limited to five minutes per clip for HD mode, and 20 minutes per clip for the latter two modes. Nikon couldn't explain the reason for the limit as of this writing, but it's likely due to sensor heating issues that might start to degrade image quality. The frame rate is 24 frames per second, and audio is monaural, not stereo. Approximate maximum file sizes of the two larger sizes both seem to be about 600-800MB. The shorter maximum recording time of the higher resolution option seems to about balance the longer recording time of the lower resolution, producing the same size files overall. Nikon says that recording will stop at 2 GB even if it's been less than the 5 or 20 minute time limit in the various modes, but we never made a file larger than 800 MB, regardless of subject choice. (Subjects with lots of fine detail will produce larger images, as the fine detail is harder for the motion JPEG processing used in the D90 to compress.)

The Nikon D90's movie recording is accessed from Live view mode: You just press the OK button to start or stop recording at any time. You have to set focus before you start shooting your movie, but you can still focus manually and adjust the zoom setting of the lens while you're shooting. The movie will record the noise of the zoom ring to an extent, depending on which lens you're using and how fast you zoom, but it's still pretty impressive. Of course, one of the big advantages of being able to record movies with a Nikon SLR is that you have the full spectrum of Nikon lenses available to you, ranging from ultrawide angle and fisheye lenses all the way to ultra telephotos. You can also obviously use special lenses like the new LensBaby Composer for special effects. (While the D90's video is more oriented toward the making of quick "video snapshots," we can imagine some pros using it just to be able to incorporate special effects like the LensBaby look into their productions.)

Frame Rate
The Nikon D90 captures images at 24 frames/second, the same frame rate used in the motion picture industry. This produces reasonably smooth motion, but we found that rapidly moving subjects close to the camera could look a little jumpy: The same as they do at your local cinema. If you've been using a digicam with a frame rate of only 15 frames/second (fairly common a generation or two back), the D90's 24 fps will be a welcome upgrade. On the other hand, if you've recently been using a digicam with 30 fps capture, you may find the D90's video a little jumpy. Once again, this probably isn't critical for "snapshot" videos, but another indication why the D90 really isn't a substitute for a dedicated camcorder.

Prior to recording, you can let the camera set focus via one of two ways: First, you could half-press the shutter button before switching to Live View mode. This will use the camera's normal autofocus system, which is quite fast. (As is typical of SLR phase-detect AF systems.) Alternately, most people will probably switch to Live View mode and do their initial framing before half-pressing the shutter button. This uses the D90's contrast-detect focusing mode, which is rather slow: Expect it to take two or three seconds, longer if it has to move the lens elements a lot.

The lack of autofocus during movie recording with the Nikon D90 is something that may give many potential owners pause, as focus is so critical in still photography and dealing with moving subjects would seem to make it even more so. In practice, we were surprised to find it not nearly the issue we expected it to be. This may be because the lower resolution in video mode greatly increases the effective depth of field: Subjects that would be well out of focus when shot at the D90's maximum still-image resolution of 12 megapixels often looked just fine when viewed at even the maximum video resolution of 1,280 x 720. Lower resolutions only increase this effect. And it's not just the resolution, either, the video compression introduces quite a bit of softness on a frame-by-frame basis, further masking softness due to defocusing.

Still, the Nikon D90's manual-only focusing in movie mode means that a whole new generation of non-professionals will now learn what it means to "pull focus" while recording movies, as the point of interest move from one subject to another, or if the subject moves significantly closer to or further from the camera during a segment. "Focus pulling" is a cinematic technique often performed by someone other than the camera operator, who is usually too busy framing the image to attend to focus as well. But millions of Nikon D90 owners will be able to try a technique that few camcorder owners can.

In our own admittedly limited playing with the Nikon D90's video recording, we found that pulling focus during a recording was a skill that required some learning, particularly if there were things going on in the scene that needed paying attention to. If we knew the approximate locations where the subject would be at the start and end of a clip (think of a video of a Little Leaguer sliding into home), we could check the corresponding positions of the focus ring and then try to repeat them while the action was taking place. This was a little hard to do with only a ring to grab onto, as the tactile reference for the different focus positions was pretty weak; a lever would have made the starting and stopping positions much more evident and easier to remember. As more SLRs capable of video recording get out into the market (Canon recently announced the EOS-5D Mark II, which also offers HD-resolution video recording), we suspect we'll aftermarket gadgets will appear that will let you temporarily attach a lever of some sort to lens focus rings, for just this purpose.

If you don't know in advance how the subject is going to move, you can try to judge focus from the image on the D90's rear-panel LCD and adjust accordingly. The exceptional resolution and sharpness of the LCD makes this more practical than it might sound. Once again, some practice (and inherently good reflexes) are required, but given enough practice, it could work reasonably well.

While not documented, it turns out you can control the aperture used for movies by selecting Aperture Priority or Manual exposure mode prior to entering Live View mode. Shutter speed and ISO sensitivity are always under the control of the camera. It appears that the D90's autoexposure during movie recording is performed by varying sensitivity and/or shutter speed in steps (1/3 EV?) rather than being continuously variable, which can lead to some abrupt, stepped changes in exposure. Only matrix metering is supported during movie capture, however exposure compensation can be adjusted up to +/- 3 EV while recording, and exposure can be locked using the AE-L/AF-L button. You can apply Nikon's Picture Controls as well as specify the color space for movies, as long as they are selected before recording begins. This is useful if you'd like to for instance record in monochrome, or with more saturated colors, etc.

The Nikon D90 has an internal microphone concealed behind three small holes on the front of the camera body. There is no provision for an external mic, nor do you have any control over the audio recording level: The camera's auto gain circuit (AGC) adjusts the mic sensitivity as needed to maintain a more or less constant recording level. We found the D90's microphone to be quite sensitive. It has no problem picking up even quiet conversation from across a room, as long as there are no background noises. Ah, but there's the rub: The mic will pick up all sorts of background noise if you're not careful. For a camera-mounted mic, there's not much else the engineers could do: The last thing you'd want in this case would be a mic with limited far-field pickup. Given that most users will likely be using the D90's video recording for short clips of memorable moments, its tendency to pick up every sound is probably a positive feature.

Rolling Shutter Artifact ("Jello Effect")
There was one aspect of the Nikon D90's video that we found less than wonderful, though, namely the way its progressive data readout from the sensor chip can produce distortions in the image when the camera or subject moves suddenly. The D90 records its movies at 24 frames/second, but the way it clocks data off its sensor chip means that it takes on the order of 1/24 second to read out each frame. By contrast, most camcorders grab each frame at a single moment in time, with all of the pixels in the image acquired simultaneously.

The consequence of this progressive capture is that any movement of the camera or subject between the beginning of a given frame's capture and the end of it will produce distortions in the shape of the image.

We first noticed this effect when panning rapidly to follow fast motion: Trees and buildings would lean opposite the direction of our panning. On the other hand, if you're panning slowly to take in a larger scene, you're not likely to notice the effect at all. More disconcerting, once we became sensitized to the phenomena, we noticed our video subjects "jiggling" slightly in response to even fairly minor camera shake as we were hand-holding the D90. Lens-based IS helps with this somewhat, but we'd be much happier if Nikon could figure out a way to grab the image data all at once and then read it off to the memory card before starting the next frame grab.

Video Examples: Dave shot some examples of video with the D90, so you can see what the different resolution levels look like. Click on any of the thumbnails below to bring up each video in a new window.

Three Video Sizes
Options include 1,280 x 720, 640x424, and 320 x 216 pixels, all at 24 frames/second
(Click on any thumbnail to launch/download the movie in a new window)

1,280 x 720 pixel video
(but JPEG compression hides detail you'd see in that size still image)
640 x 424 pixel video 320 x 216 pixel video

As noted earlier, the Nikon D90's video imagery is not only considerably lower resolution than its still images, but the heavy JPEG compression applied to the video frames further reduces detail. The upside of this is that the effective depth of field is quite a bit greater than you'd find in its still images at similar focal length and aperture. Note in some of the shots how little the apparent focus changes as wonder-dog Charlotte runs toward or away from the camera.

In the highest-res shot above, the lens was initially focused somewhere between Marti and the camera, so she's a little soft at the start of the clip. That said, I found it quite surprising how little apparent sharpness changed as Charlotte ran approached and receded from the camera.

Jello Effect
(Rolling Shutter Artifact)

Rapid camera motion can result in pretty severe distortion and apparent subject motion.

You wouldn't pan like this, but notice how even normal camera shake translates into subject jiggling.

As mentioned earlier, the Nikon D90's "rolling shutter" can introduce pretty severe distortion in response to either camera or subject movement. The clip above is an extreme worst case: You'd probably never film with this kind of extreme camera motion, but it illustrates the nature of the problem pretty clearly. Notice how it's really not noticeable when panning slowly. Notice too, though, how even relatively minor hand movements at the end of the clip still create some distortion.

Pulling Focus
Manual focus while recording is challenging, but can be learned.

I wasn't quite quick enough to follow the butterfly here, but with practice, it shouldn't be too difficult to learn to pull focus for the D90's videos.

I didn't have much time to devote to sharpening my focusing skills with the Nikon D90 in video mode. (Nor, for that matter, my skills in tracking small, rapidly moving subjects. :-) Nonetheless, this clip shows that it's not too difficult to focus based simply on what you're seeing on the D90's excellent, high-resolution LCD screen.


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