Optical Zoom vs. Digital Zoom: Quality vs. Quantity

by Jack Kabza
Published on Nov 10, 2005 3:00 PM



Wow! As you flip through your new camcorder’s manual, you notice that it has a good 25x optical zoom, but a gigantic 700x digital zoom. 700x! Visions of spying and subterfuge dance in your head—just think of what you could capture with a zoom like that. How about the text on important government papers, seen from the next office building away? Or what people are wearing at the base of the Sears Tower, while you stand and watch from the comfort of the Skydeck? …Or maybe not. Sorry to cut short your magnified fantasies, but optical zoom and digital zoom are two entirely different animals. Zoom is zoom, right? Wrong. Here’s why.


This is video shot at 10x optical zoom at a distance of about 10 feet.

Optical zoom works the same way as a magnifying glass or a microscope. When you put a magnifying glass over an object and light passes up through the lens to your eyes, the curvature of the glass causes the light rays to bend and expand, thus spreading out the appearance of the detail on the object below and making it appear larger. Detail that may get lost or “swallowed” when light rays are more crowded together becomes more apparent. Instead of seeing a little, creepy bug beneath your magnifying glass, you can now see a BIG creepy bug, as well as all the joints on its legs, the texture of its wings, and the structure of its mouth parts.

Digital zoom is a little more difficult to explain. To understand how it works, let’s use an example from art history. (No, really.)

In France, during the1880s, there was an art movement called Pointillism. The style consisted of pictures which were painted not with long smooth brush strokes, but by dipping the very tip of a brush in paint and creating a picture by painting thousands upon thousands of tiny spots, in many different colors. From a very great distance, the human eye cannot distinguish these separate spots, and the colors of the spots appear to blend together into many different shades and tones into a unified image.

          
The picture on the left is video taken from 10 feet away at about 100x digital zoom. Note the pixelation. The picture on the right was taken at 10x optical zoom from a distance of about 4 feet. There is more detail than in the picture above, but no pixelation.

This is roughly analogous to how a camera’s sensor sees the world, with the pointillism spots analogous to the pixels in a digital image. The individual pixels are so tiny that the human eye cannot distinguish them, and the image appears to be very smooth.

Digital zooming is like taking steps closer and closer to a pointillist painting: the closer you approach, the easier it is to see all the individual dots of color—and the more you digitally zoom, the larger your colored pixels appear.

Consider this image of George Seurat’s pointillist painting, “La Parade”: http://www.mcs.csuhayward.edu/~malek/Seurat4.html

Though the painting has a slightly fuzzy look, as per the style, we can still make out a coherent whole image. Now consider a close-up detail of part of the same painting, found from a Wikipedia article, here: http://en.wikipedia.org/wiki/Image:Seurat-La_Parade_detail.jpg

We can still discern what this is supposed to be, but it’s much messier and it takes some work… and if you use digital zoom on your camcorder instead of optical zoom, your far-away shots of Uncle Hal are going to look an awful lot like this.

So what good is digital zoom? That’s a good question. We here at CamcorderInfo.com are convinced that digital zoom only benefits the manufacturer, because it’s another big number to stick on a spec sheet and trick unwary consumers into thinking they’ve snagged a good deal. But who knows—maybe the industry has been holding its breath all this time, secretly hoping to help encourage a new generation of pointillist videographers.

But somehow, we doubt it. When you’re looking to buy a camcorder, the best way to treat a model’s digital zoom is to simply ignore it.