DSLR (Digital Single Lens Reflex) cameras with video capability are all the rage these days. It seems that every announcement for a new DSLR includes the camera’s formidable video recording capabilities, as if you don’t need to do anything other than point your camera to make great video. If only it were so.
There are many reasons to use DSLRs to make video for eLearning, not the least of which are the stylish quality of the video they can shoot, the range of lenses, and, of course, the additional control of composition you can gain. Recently, I suggested that readers shouldn’t use a DSLR for video production in eLearning. Am I recanting my previous statement? In a way, yes. I’m now advocating the use of DSLRs for creating e-Learning video, but there are still lots of caveats. And at the same time, it remains a lot easier to use your handy dandy camcorder to make video because DSLR’s are not ready for easy video production.
The key word is “easy.” Each brand of DSLR has its quirks and individual video formats, and not all DSLRs can record broadcast-standard video in SD or HD (standard or high definition). If your end result is for Web consumption only, then SD and HD are not a consideration. But when capturing your video into your editing program, it can be painful if you don’t know the exact digital video format. Canon, Nikon, and Pentax all record in different sizes and formats. In fact, even for a given manufacturer, different camera models record in different formats and image sizes.
What DSLRs can do
The thing to remember is that DSLRs are first and foremost devices for creating still photographs (although that’s changing). Can they really record video and do it well? Do they have enough digital “horsepower?” The answer to both questions is “yes.”
Doing the math
Mid- to upper-end DSLRs can take four to seven or so frames of still images per second in RAW format. (Editor’s Note: explanations of a number of technical terms in this article are in the last section.) Most DSLRs run out of buffer space after 14 to 20 or so images (this varies widely from camera to camera). That’s the number of frames in about a half second or so of video, hardly the 24, 25, or 30 frames of progressive video a camcorder easily shoots.
Does this mean a DSLR doesn’t have the horsepower to shoot video? No. There is a tremendous amount of information recorded in a still image file in RAW format — video does not contain nearly as much data. Let’s compare the number of pixels in one second of full HD video to the number of pixels in the five full-frame still images the same camera could record in one second.
Full HD video (also called 1080p) at 30p (thirty progressive frames of video per second) requires a DSLR to process and write to memory 62,208,000 pixels of information per second. If that DSLR has a 14 megapixel (MP) sensor, at full frame rate (5 frames per second) the camera needs to process 70,000,000 pixels of information per second. Obviously, the DSLR can handle the raw pixel processing power.
So what’s the difference? A single 1080p frame consists of 2,073,600 pixels. If you’ve got a 14MP sensor, you’ve got a whole lot more pixels. (Almost seven times as many!) The sensor must use the same pixels each time it records a frame or you would get a kind of strange stroboscopic shift because the camera would record the frame from a different spot on the lens as it focuses on the sensor. This is enough to give me a headache, but the bottom line is that the video recorded can be beautiful, even if it is a little more complex to create.
The benefits of the DSLR for video
Now that you know the technical difficulties, what are the advantages of using your DSLR camera to shoot video? There are five main benefits.
Low light sensitivity: DSLR cameras have a setting for ISO (light sensitivity) and each generation of DSLR does a better job of handling high ISO (low light) settings with less pixel noise in the backgrounds. In practical terms, this means you can shoot with less light in any given scene.
Sensor size (see Figure 1): Sensor size matters because sensors and their interaction with light are kind of funny things. At the top end of the price and quality range (at least for cameras that cost less than $25,000), most camcorders have tiny sensors, even when they have three. At the other extreme of the range, you can use a point-and-shoot camera to record video. Such a camera generally has a teeny (1/2.3 inches) sensor, enough for about 10–14 megapixels these days. In the middle of the range, cameras use an APS-sized sensor that has 14MP. Or you can use a full frame camera. “Full frame” refers to the size of a 35mm film frame from the days when you still loaded film into your camera. Full frame sensors run from about 14MP to 27MP.
Figure 1. Relative sensor sizes in digital cameras.
Is there a difference? In two words: “You bet!” The first reason is the size of the pixel site. A full size or APS-C sensor is between 9 and 40 times the size of a typical small camera sensor. If the number of pixels is the same, what’s the difference? It’s the size of the pixel site. If a given teeny sensor has 14MP and a big sensor has the same number of effective pixels, then simple math shows the pixel site is far larger. Why does this matter? It all has to do with photons, particles of light. A photon striking a pixel site on a tiny sensor will bounce around a bit before being absorbed by the baffles around the sensor. The light can “bleed” over into another sensor because the site is so small to begin with. This creates noise in the image because an individual sensor will probably be struck more than once. A larger sensor gets less photon “bounce,” so in theory it has less noise. It also works out in practice, especially in the case of pixel sites that are 12 (or more) times larger on the bigger sensor. Less noise means a clearer picture and greater low light sensitivity. So large sensors create images with much less noise than small sensors.
There is one additional reason larger sensors work better for videography. It has to do with the combination of sensor and lens. A small sensor can’t show the depth of field a lens can record. There are many reasons for this. We generally use a 35mm frame size as a reference point. A small sensor, say 1/45th the size of a 35mm frame, crops a picture a lot with a given lens focal length.
Think of it this way: the field of view with a 55mm lens (considered a “normal” lens in 35mm photography) is X-degrees wide for any given lens or aperture. Aperture is the amount of light the lens lets through. The higher the aperture number, the lower the amount of light and the greater the depth of field. Long (telephoto) lenses have shallower depth of field than wide angle lenses. When you couple a long lens to an APS or full frame sensor, you can get a very shallow depth of field, which allows you to make the area of focus the important part of the picture. Small sensors, since they use only a smaller part of the sensor, have HUGE depth of field compared to the image from a large sensor. An additional difference is that a small sensor on a camcorder can’t use different exposure values, so it can only shoot practically with a lens aperture of about f5.6 or so. And since that small sensor only uses a small angle of view, sometimes called the “crop factor,” it makes a wide angle lens, which usually would have a wide field of view, into a telephoto lens, in a manner of speaking. This means subjects both close and far are in focus. In other words, the smaller the sensor, the smaller the angle of view. When you shoot with a small sensor, almost everything is either in focus or out of focus.
Lenses: If you have a DSLR (or an old film SLR for that matter) and an investment in lenses, you understand this benefit. Lenses are an incredible asset for creating video. A good DSLR (or film SLR) lens is generally far better quality than a camcorder lens. If they’re in your equipment bag, you can use true telephoto, macro, or wide angle lenses to create images that you really can’t create with a camcorder. And you can do it with the same style you’d get when shooting still images. The idea of using a telephoto lens to shoot a person from a long way off is intriguing. The person would be in focus and the background out of focus (at fairly wide aperture settings, say up to f8 or so). There is a somewhat overused word for this kind of focus on your subject. It’s called “bokeh,” which refers to parts of the image being blurry, which brings us directly to the next benefit.
Style: The above benefits together provide an immense gain in image control. If you want the whole image to be sharp and in focus, then use a wide angle lens with a focal length of 24mm to 35mm. If you want selective focus, anything above an 80mm lens and higher with an APS or full frame sensor will give you the kind of soft backgrounds or foregrounds you want. “Telephoto” usually refers to a lens that’s over 120mm focal length. But a 200mm or 300mm lens is even better and has less depth of field. This is control. And if you want to create great images, you need control. The range of lenses available for DSLRs is staggering. In addition to control over focus, this range greatly increases the number of situations in which you can shoot video. There are lenses that excel in low light situations. There are other lenses that are ideal for outdoor settings where there is so much light that overexposure is a concern.
Manual control: One of the features of shooting in video mode on a DSLR is that the camera switches to manual mode. The mirror goes up and you can only use the viewfinder on the back of the camera or an external monitor. This is a downside for some people, but it adds to the amount of control you have.
For example, you control white balance when in manual mode. White balance is a camera setting that adjusts for lighting so that white objects appear white in your video. Most modern camcorders have “automatic” white balance, which means it can change anytime you’re taking a shot.
You’ll also do your own focus because autofocus is often shut off when your DSLR is in video mode. (Note that the new models from Canon and Nikon, however, can use the autofocus when shooting video.) Personally, I like to focus manually, as it gives me more control. You’ll need to or should set the aperture as well. All this manual control goes back to style; you control the entire exposure process.
The drawbacks to DSLR
As you’ve seen, there are lots of plusses when shooting video with a DSLR. What are the minuses? There are four that you should pay attention to:
Additional equipment: Yes, you’ll need some additional equipment. I’ve included a small list of essentials in the next section, but you can go pretty crazy with additional “accessories” for your DSLR. Some people spend $5,000 (or more) on additional equipment.
Know your camera: You really need to know your camera and what it can and can’t do. When I got my first DSLR, I immediately decided I wanted to use manual control as much as possible when shooting stills. I normally shoot SD video and use a Canon XL-2 for that purpose. In manual mode, I have complete control over the camera. And I almost always shoot in manual mode, so I’m used to shooting that way. By the way, there are excellent light meters in DSLRs, so you can see if the image is under- or over-exposed at the ISO setting you use. But manual is a downside if you just want to point and shoot.
Codecs: This goes back to knowing your camera, but you really must know the codec you’re shooting with and whether you have any control over it. You usually won’t have any control, at least not yet. Nikon has been using a form of QuickTime with the H.264 compressor, Canon has been using mpeg4, and Pentax has been using .avi (compressed) and motion jpeg. All very confusing. But once you get used to one camera — it’ll change again!
Manual control (see number 5 in the list of benefits): Some people really don’t want to shoot manually. Sometimes I’m one of those people. Sometimes the situation doesn’t allow me time to set up shots, figure out if I want a large aperture with shallow depth of field or a small aperture, etc. If I just need to shoot and get the shot, I leave the whole gizmo (DSLR or camcorder) on as much automatic as I can. It’s really up to you.