How can you work out the equivalent of optical zoom to focal lengths? , what is the difference between the two?

Lyman Gauld: here's where the **x comes from on point and shoots. Divide the Maximum focal length in mm by the minimum focal length in mm. So, if your P&S camera has a 20-400mm equivalent lens, it's a 20x lens because 400/20 is 20. On an SLR camera, we have the power of interchangeable lenses so we don't really worry about huge zoom ranges, as they're generally not very sharp or very fast. extremely good zoom lenses on a SLR (such as the 12-24, the 70-200, or the 200-400) are only 2x or so lenses, but they have much greater zoom than your P&S does. SLR owners use the much more useful focal length of lenses to describe their field of view as opposed to the **x that P&S manufacturers use as a marketing ploy. Hope this helps!...Show more

Coleman Ocegueda: The optical zoom factor is the longest focal length divided by the shortest. This doesn't tell you how wide or long the lens can see, but just the difference between these two extremes.Focal length in practical terms ! is a measure of how the lens "magnifies" the Field of View (what is seen). Lenses can be broken down into three basic types: wide angle, normal, and telephoto. Normal are basically no magnification. They give you a perspective similar to the human eye. Telephotos, which are focal lengths above normal, give you a narrower ("zoomed in") FOV. Wide angle lenses, lengths below normal, give you a wider FOV.At which focal lengths a lens is considered wide angle, normal, or telephoto actually depends on the size of the film or sensor. With a 35mm film camera around 50mm is normal. With most digital SLRs though normal is about 28mm. For simplicity's sake digital P&S cameras usually offer their focal lengths in 35mm film equivalents....Show more

Connie Dickirson: The focal length is the length in millimeters between the focal plane (sensor/film) and the further-back lens found in the lens barrel.The focal length defines the optical zoom. As the distance increases (higher mm), t! he optical zoom increases.How can you calculate optical zoom v! alues in terms of "x" using the focal lengths?By dividing the highest mm value by the lowest one.For instance, if you have a 18-55mm lens, you divide 55 by 18. The result is around 3x.This means that when the lens is at 55mm, it will provide around 3 times zoom as the image you'd get with the 18mm setting....Show more