Time to Define: HDSLR

In 2008, the HDSLR did not even exist.

Digital SLR cameras were exceptional at taking STILL images, but not a single one could be used to capture a motion picture.

All that changed at the end of 2008 with the release of the Nikon D90, the first digital SLR that could capture both stills and video.

After that first offering, the race was on: every other camera company had to produce something similar in order to stay "current".

But some new term was required to describe these cameras: they weren't really simple digital SLRs anymore, nor were they video cameras (since you can't change out the lens on most consumer video cameras).

And so, a new name emerged: welcome to the world of the HDSLR.

HDSLR Jargon

With the addition of a video mode, consumers are now faced with a whole new slew of jargon to get a handle on before deciding on a camera. You're no longer trying to decide which one will capture great stills, you've also got to figure out the quality of its video.

There are two numbers and one letter that tell you just what type of video a camera can capture:

  1. One number is the video resolution (the size of the video image)
  2. One number is the frame rate of the video (expressed in frames or fields per second)
  3. The letter tells you how the video image is scanned

Let's take a closer look at each one of these in turn.

Video Resolution

The term used to describe the size of a STILL image captured by a digital camera is the megapixel count (where mega = million). For example, a 10 megapixel photo measures 3,888 x 2,592 individual pixels (you multiply the two to get 10 million pixels).

Now, there are a LOT of different megapixel counts out there: 10, 12, 14, 16, 18, 20, etc.

The good news about video sizes? There are just TWO:

  • 1080 — this video image measures 1920 x 1080 pixels (also called Full HD)
  • 720 — this video image measures 1280 x 720 (all called HD)

Having a camera with a high megapixel count is really only important if you want to make large prints. The same sort of applies to video resolution: it depends on how you're going to watch the video.

If you only plan on watching your HDSLR video on a computer monitor, then there should not be a huge difference in quality between 720 and 1080.

However, if you'd like to playback your video on your 55 inch widescreen HDTV, then the larger size of 1080 might make a difference.

Scanning Type

There are two different ways that a video camera can capture a moving image:

  1. One complete frame (screen) at a time
  2. One frame separated into two fields (displayed in rapid succession)

The first approach is called progressive scanning (p) while the second is called interlaced scanning (i).

Interlaced scanning was developed to keep older tube televisions (also called Cathode Ray Tubes or CRTs) bright by alternating one field of even scan lines and one field of odd to create a single frame of video.

Since the interlaced images are displayed so rapidly, the persistence of human vision sees a complete frame of video on the screen.

With the arrival of LCD computer monitors and flat-panel televisions — both of which scan a single complete frame at a time — progressively scanned video has become much more common.

Are there any real differences?

The only visible one is that sometimes an interlaced video will look blurry (an effect called "ghosting") when the camera is tracking a fast-moving subject.

So: if you're really into creating fast-action videos then getting a camera that captures progressively scanned video might be a better bet.

Frame / Field Rate

We now arrive at the second number in all HDSLR notation: the frame rate or field rate.

The one that is used depends on the scanning type: since interlaced scanning splits a single frame of video into two fields, the frame rate is expressed in fields per second. Progressive video is expressed in frames per second.

There are two frame/field rates that are the most common:

  1. 24 frames per second / 48 fields per second — this is the frame rate of most movie cameras. Shooting video at this frame rate looks more "cinematic".
  2. 30 frames per second / 60 fields per second — this is the frame rate of standard video cameras and what most people are used to seeing when watching home movies.

Should you be deeply concerned if the camera you're considering only has a 30 frames per second option? Not really.

Unless your whole purpose for getting the HDSLR is to create independent short films, the difference should not matter and there's no impact on video quality.

However, there ARE some frame rates that CAN be important: those that are faster than 30 frames per second.

If a camera is capable of capturing video at - say - 100 frames per second, when you play this back at a "normal" speed what you get is super-slow-motion video. This can be a neat effect and can add flair to what might otherwise be just another boring vacation video.

Putting it All Together

Now that you have a handle on video resolution, scanning and frame rate, let's put it all together by looking at some common shorthand for describing HDSLR video.

When looking at a new camera, here's how you might see the video mode described: 1080p30.

  1. The first number 1080 tells you the resolution is 1920 x 1080
  2. The "p" tells you the scanning is progressive
  3. The 30 tells you that the frame rate is 30 frames per second

Let's look at a few more examples:

720p301280 x 720Progressive30 frames per second
1080i601920 x 1080Interlaced60 fields per second
1080p241920 x 1080Progressive24 frames per second

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