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The zoom power of a lens has no meaning except as the relationship between the longest and shortest focal length of the lens.įor instance, even on a bridge or ultrazoom camera, one camera being marketed as a 30X zoom and another as a 28X zoom doesnt tell you whether the longest field of view is longer or the widest is wider, just that the lens has a greater range between the two.
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That said, I never saw a definition of zoom range w.r.t change in FoV. However, as you get to the wider side, the angles become large and the mapping from focal length to angle of view is nonlinear. Thats because zooming is mathematically like cropping, so each doubling of focal length is halving dimensional field of view in a very straightforward way.įor relatively long focal lengths, the angles are small and the change is approximately linear. This was generated at and the diagonal was made simply with the hypotenuse algorithm hxy. Zooming 2mm in when at 17mm will result in a much larger change in the field of view than zooming 2mm further at 200mm. In some ways, giving the angle of view instead of focal length might be preferable, but that hasnt really caught on probably because its really not very hard to get a sense for what different focal lengths mean for field of view on your own camera, once you get over the initial learning bump.Īs you zoom in with linearly in millimetres, the actual field of view change is not linear. Intermediate and advanced users may prefer to be given the straightforward facts instead of having to decode more-removed numbers like times-zoom. That can be intimidating to would-be photographers who want to concentrate on images, not tech stuff.Ī simple number, without any metric-system units, is far less intimidating than needing to learn all about focal length and angle of view, so I dont think the marketers are all wrong to focus on this number for basic cameras. There is no standard base number that the starts from you go from whatever the widest focal length on that particular lens happens to be. That made the times-zoom a reasonable way to compare how far one can zoom in to get a closer view of a distant subject.