November 30, 2009

HD DSLRs: nice pictures, nicer price

One of the most exciting developments of the past year, for those whose ambition is larger than their budget, has been the introduction of HD DSLR cameras, most notably from Canon. These allow the use of lots of relatively cheap, high-quality lenses with an APS-C (about 23x15mm) or even 35mm (36x24mm) sensor that can capture beautiful images for less than the price of a Sony EX1 or other low-budget professional camcorder. The APS-C sensor has about 5.5 times the area of a 2/3-inch sensor used in most mainstream broadcast cameras (and about ten times the area of a half-inch sensor used in the EX1 - although broadcast cameras usually have three such chips so performance isn't exactly comparable).

As HD DSLRs are designed primarily for stills photography, they don't have the ergonomic layout you'd expect from a video camera, and there are limitations in what controls you can use while recording and in facilities (especially audio). The choice of recording codecs is not always ideal either. But low-light performance is often excellent, and they are particularly useful for stop-frame animation or time-lapse videos.

Virtually all CMOS sensors used on DSLRs (as with most low-end camcorders) exhibit rolling shutter artefacts (when the camera is panned any vertical lines in the picture will wobble while photographic flashes may only occupy part of the picture). High-end digital cinema camcorders typically use a global shutter (which electronically shutters all pixels simultaneously) or simply readout fast enough from top to bottom to reduce or avoid it. However, it is certainly a problem with the current crop of HD DSLRs, necessitating slower panning speeds, the use of Steadicams or shake reduction technology for hand-held shots, or fixing the problem in post, with the likes of The Foundry's RollingShutter plug-in for Nuke and After Effects (watch a video about RollingShutter).

A further issue is audio. Many of the higher-end cameras have a mini-jack input for mono or stereo audio, some rely on inadequate built-in mics. However, it is generally best to work with them like a film camera and record audio separately.

There are also restrictions on the length of clips that can be recorded at one time (12 minutes on the Canon EOS 7D, for example), possibly to avoid sensor heating or power problems, and users have to be careful to buy memory cards that are fast enough that they will record all the way through without problems (there can be a big difference between card manufacturers on this, with some performing better at a lower stated class than others do at a higher classification).

If you're wondering what difference would it make buying a 35mm sensor over an APS-C or broadcast 2/3-inch sensor camera: 35mm will give you shallower depth of field (less of the picture in sharp focus - and more of it, especially the background, pleasingly blurred). However it can also be a nuisance. You can set up a shot, have the subject perfectly in focus, start shooting and he's moved back or forward slightly and is now out of focus. In most situations, you'll be able to get as little depth of field as you'll ever need with an APS-C sensor (and often even with 2/3-inch chips). Of course, the larger the sensor, the better quality image you should get - especially in low light, as the pixels aren't as closely packed together (but a 25megapixel 35mm sensor will have about the same pixel density as a 10 or 11MP APS-C sensor), and you're only going to be shooting at 1 or 2MP for HD video - so how the recording codec performs may have a bigger impact on your video quality than the sensor size.

Playing the field

The camera that started this trend is Canon's EOS 5D Mark II (the first 35mm HD DSLR - pictured top in use with a Vocas DSLR rig), which is ideal for anyone who wants shallow depth of field at the lowest price possible.

It currently records 1920x1080 at 30 frames per second (which has been a problem for those of us in Europe, although that can be dealt with – look at filmmaker Philip Bloom's website for suggestions). However, that will be rectified early in 2010 when Canon promises to update its firmware to allow 24 and 25fps. It has already updated the camera to allow full manual exposure while recording video.

[UPDATED: The 24/25fps update (firmware 2.04) is now out and also adds full manual audio controls.]

The new Canon 1D Mark IV already has full HD at 24, 25 and 30fps (plus 720p/50 and 60), but uses a slightly smaller 1.3x crop sensor (APS-H - although its performance in low light seems to be particularly good). The recently introduced Canon EOS 7D offers the same formats on a less expensive APS-C model (about 1.5x crop). Files are saved using AVC/H.264 compression in a .MOV container (at about 44Mbps for full HD), with Linear PCM 48KHz audio.

[UPDATED: There is also now the Canon EOS 550D (Rebel T2i in the US), which is smaller and lighter (and about half the price for the body) than the 7D, but offers the same video formats on the same sensor - although it isn't as feature rich as a stills camera as the 7D.]

Although Canon is the key manufacturer of HD DSLRs, others have entered the market.

The APS-C Nikon D90 was the first DSLR to record HD video, at 720p/24, as now do Nikon's 35mm D3S and APS-C D300S and D5000 models, using AVI Motion-JPEG codecs.

The compact Pentax K7 is another APS-C 720p camera, but only at 30fps (AVI Motion JPEG at about 45Mbps variable), although it can also shoot at a non-standard higher resolution (1536x1024 - 3:2 aspect), however the even smaller Pentax K-x records 720p at 24fps, has very good low-light performance, and is currently about the cheapest HD DSLR available. Both Pentax models benefit from in-body shake reduction, which means that they can be used hand held with inexpensive, old prime lenses.

The Panasonic Lumix DMC-GH1 has an interchangeable mirrorless lens system, which means it can be smaller than conventional DSLRs, although it also has a smaller (Micro Four Thirds) sensor with a 35mm crop factor of about two. It seems to be the only "HD DSLR"* that can auto-focus while recording video, although that should be less important for anyone coming from a video or film background than it seems to be for stills photographers moving up (although autofocus only works with certain lenses). It records 1920x1080 at 50/60i or 24/25p using AVCHD (about 17Mbps), or can record 720p/50 AVCHD or 720p/25 using Motion JPEG (.MOV at about 28-30Mbps). Tests show a lot more artefacts in 1080 than with 720, which isn't surprising as the bitrates are the same. There is also the cheaper Panasonic GF1 which only records 720p/60 and 30.

*Note: Of course the Panasonic isn't a DSLR - as it doesn't have a mirror (the Reflex), but as it has interchangeable lenses it should probably be included here....

Related Posts: Cheap 35mm video - Canon cuts cost of HD - HD DSLRs: Still developing

By David Fox

1 comment:

  1. David mentioned the forthcoming EOS 550D at BVE last week, here is the first hands-on review I have found with video example: