WARNING: This article is for digital cinematographers/filmmakers (or aspiring ones). Anybody else will just be bored to death by the technical mumbo jumbo.
NOTE: The Canon T3i, at this time is the only Canon DSLR with this feature. The 60D had something kind of like this but far inferior. So this one feature makes the T3i “better” than all the other Canon DSLRs, including the 5D Mark II, in some specific shooting scenarios, such as being able to get macro shots without a macro lens. I still like the full-frame look for some projects however.
If you’ve ever had a consumer camcorder or point and shoot camera that recorded video, it probably had a feature called “digital zoom” which made the image quality worse, as it basically cropped into the actual pixels of the image and upscaled them. This was a far worse alternative than “optical zoom,” which referred to using a zoom lens, and didn’t mess with the pixels.
Well the “Movie Digital Zoom” feature on the Canon T3i/600D doesn’t have anything to do with that. Instead of cropping into the limited number of pixels of the final image, it actually does something that makes a lot of sense: instead of sampling the whole 5184 × 3456 pixels of the T3i’s 18 Megapixel sensor, and then line-skipping (as opposed to other more legitimate ways of downsampling) down to the 1080 x 1920 pixels that comprise a 1080P image, it actually just samples the 1080 x 1920 pixels from the middle of the sensor. Ergo, no downsampling at all is required, and the final image is pixel for pixel what is being exposed by the photosites on the chip. Sounds much better than a line-skipped image right? In many ways it is. One drawback however is that you are not using the whole lens and therefore lower quality lenses may not be able to resolve as much detail in just that small portion of the lens. But I used Digital Zoom with a Canon 1.8 50mm on 30% of my short Christmas film Riverwoods (watch it here), and I think those shots turned out great.
Besides turning a “normal” 50mm lens into a 150mm telephoto lens, another major advantage is that it also turns such a lens into essentially a macro lens. If I were to use a 50mm lens, even on a crop sensor, with it’s minimum focusing distance of 18 inches, it is impossible to get an extreme close-up (or ECU) of say, a human eye. When you get the camera that close to the eye, it can’t focus. However, with the Digital Zoom feature, you don’t need to hold the camera nearly as close if you want the eye to fill up the frame. Holding the camera at 18 inches away, and using Digital Zoom gives you a pretty nice macro shot of the eye. (Of course, this can be used for ECU’s of all kinds of things, an eye is just an example.)
Here is a short unscientific comparison to illustrate this point. It’s unscientific because I did move the camera a bit in between shots. However, clearly the second shot would be impossible without the Digital Zoom feature. [Note: You should always use the 3X setting on Digital Zoom, anything higher will crop into the final pixels and degrade image quality!]