On Photography
Inching toward the metric system
By Robert de Gast

The metric system, a gift from the French, has been around for more than 200 years. (If you really want to know, here’s the definition of a meter: the distance light travels through a vacuum in 1/299,792,458 of a second. That’s roughly 39.37 inches. Remember, you read it here first!)

Every country in the world but three uses this elegant, user-friendly measuring method. The hold outs? Liberia, Myanmar and the United States. Mexico, of course, has been in the metric mode since shortly after Independence; that’s why we buy a litro of wine, a kilo of cheese, a hectare of land and, until recently, made photographs with 35 millimeter cameras. (The “35mm” refers to the width of the film.)

But even though we have entered the digital age, allusions to the metric system remain with us in the digital photography world.

For example, when the notation 35mm appears on the front of the lens, it refers to the focal length and indicates the angle of view the lens produces: a 35mm lens produces an angle of 63 degrees, a 50mm lens gives approximately the same coverage as human vision, a 100mm lens an angle of 24 degrees, and so on. Lenses are made in many focal lengths ranging from 6mm (180 degrees) to 1000mm (2.5 degrees). Most point-and-shoot cameras have zoom lenses with a range of 63-21 degree angle of view.

However, if you are the owner of a digital single-lens-reflex camera (DSLR), things get a bit more complicated.

For reasons of cost, the sensor in most DSLR cameras (that is, those costing less than US$2,000) is smaller than the size (24x36mm) of a 35mm film image. Thus the focal length of the lens has to be multiplied by 1.5 for Nikon DSLRs and by 1.6 for Canon cameras. The multiplier for Olympus cameras is 2x.

That means that, for example, if you’re thinking that your old Nikon film camera lenses will fit on your new digital Nikon body, you’d be right, but that 24mm wide-angle lens has now become a much narrower angle 36mm lens.

On the other hand, your 200mm telephoto lens is now a 300mm lens. Here’s your chance to get away from those close-ups of flowers and become a wildlife photographer!

Despite the nearly universal acceptance of the metric system, it is interesting to note that photographic print sizes continue to be expressed in inches: we have 4x5, 5x7, 8x10, 11x14 inch prints, and so on.

This probably reflects the (past) dominance of US photographic paper manufacturers and the staggering number of photos made in the US when compared to other countries. This is likely to change in the years to come, though.

So, treasure the measure!

Robert de Gast is the author, most recently, of Behind the Doors of San Miguel. He offers short photography tutorials and leads small workshops. He can be reached at 152-7396 or via e-mail at robertdegast@hotmail.com.