But Don’t Forget the Crop Factor

From time to time you’ve heard the term crop factor, and you’ve probably also heard the term lens multiplier factor. Both are misleading and inaccurate terms used to describe the same phenomenon: the fact that cameras like the Sony Alpha (and most affordable interchangeable lens digital cameras) provide a field of view that’s smaller and narrower than that produced by certain other (usually much more expensive) cameras, when fitted with exactly the same lens.

Figure 8.1 quite clearly shows the phenomenon at work. The outer rectangle, marked 1X, shows the field of view you might expect with a 100mm lens mounted on a socalled “full-frame” digital model like the Alpha DSLR-A850, or a 35mm film camera, like the 1985 Minolta Maxxum 7000 (which happened to be the first SLR to feature both autofocus and motorized advance, something we take for granted in the digital SLR age). The rectangle marked 1.5X shows the field of view you’d get with that 100mm lens installed on a Sony Alpha SLT-A65. It’s easy to see from the illustration that the 1X rendition provides a wider, more expansive view, while the other one is, in comparison, cropped.