BetterPhoto Q&A
Category: New Answers

12x compared to 18x

To love this question, log in above
August 01, 2007

I will lay the basis of the math out for you, you can do the rest.

Over the years the camera has evolved using the human eye as a model. Our eye brain combination yields an angular field of view of about 53°. The camera duplicates this angle of view when the lens employed operates at a focal length about equal to the diagonal measure of the film or chip employed. As an example the 35mm film camera uses film that measures 24mm height x 36mm length this computes to a diagonal measure of about 43mm. Most 35mm cameras sport a normal lens that is 50mm in focal length. This is a rounded up compromise. A full frame digital chip has the same diagonal measure. Most other digitals sport smaller chips. While their is no standard most are 66% or this value or about 28mm as to diagonal measue.

Your digital camera likely will produce a normal angle of view when the lens used hovers around 28mm. Now the modern cameras sport a zoom lens which allows the user to change focal length. Shorter than 28mm is in the realm of the wide angle and longer is telephoto.
If the zoom range provided is 14mm thru 56mm we calculate the range by simple division. Think about 56 divided by 14 = 4. This is the zoom range written as 4x.

Say your camera sports a zoom lens that tops out at 200mm focal length and bottoms out at 25mm focal length. The math is 200 divided by 25 usually written as 200 / 25 = 8x.

Thus if your camera sports a zoom that tops out at 300mm and bottoms out at 20mm the zoom rage is 300 / 20 = 15x.

Another aspect:
Often a digital camera employ additional magnification in the form of electronic zoom preformed by software in the camera (chip logic). This might provide an additional 2x or 4x more magnification. Thus a system with an 8x optical range now extend to 16x or 32x when we multiply by optical zoom range by the electronic zoom range.

Alan Marcus (beware I am known to provide marginal technical advice)
ammarcus@earthlink.net

To love this comment, log in above
August 02, 2007

To love this comment, log in above
August 02, 2007