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Old Jan 19, 2007, 10:53 AM   #1
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I'm looking at an SLR camera that comes with a 18-55 mm lens. What is this equivalent to when comparing with optical zoom on a point-and-shoot digital camera?
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Old Jan 19, 2007, 11:08 AM   #2
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Depends on the camera you'll be using it on.
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Old Jan 19, 2007, 2:52 PM   #3
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You will want to find out the 35mm film camera equivalent zoom range in millimeters for both this DSLR camera/lens combinationand the point and shoot camera you are comparing with. This information should be published in the camera's instruction manual if the lens came with the camera.

Most point and shoot digitals have 3x optical zoom ranges of between 35 to 105mm and 38 to 115 mm in 35mm film camera equivalents.

The 35mm film camera equivalent zoom range is the zoom range stamped on the lens trim ring multiplied by 43-1/4 (diagonal of a 35mm film frame which is 24x36mm) and thendivided by the diagonal in millimeters of the sensor of the camera the lens is meant for.

Useful digital camera hints:


After you determine the 35mm film camera equivalent focal length range for an interchangeable lens, if you take the lens off and put it on a secondcamera, you must recompute the 35mm films camera equivalent by taking the previous 35mm film camera equivalent, multiply by thediagonal of the first camera's sensor (or film frame)and divide by the diagonal of the second camera's sensor.

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Old Jan 19, 2007, 2:57 PM   #4
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the problem with the "optical zoom" of P&S is that it's completely bogus marketing term. It does not tell you anything about how close or how wide the lens cover, all it tells you is the ratio of the telephoto end and the wide end. In that case, the 18-55 is 3x since 55 / 18 = 3. A 50-150mm is also 3x and a 200-400mm lens is 2x even though it has more telephoto capability.

So as you can see it's completely useless term.

The best thing to do is to look at the P&S camera's specs and see what focal length is covers in the 35mm format.

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Old Jan 20, 2007, 12:49 PM   #5
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Most dSLRs (except full-frame ones) have a conversion factor that stems from the smaller-sized sensor. You use this multiplication factor to calculate the 35mm equivalent focal length. This factor differs between various brands of cameras and the sensor used. For example, Pentax and most Nikon dSLRs have a conversion factor of 1.5x; others may have a 1.6x conversion factor.

So to calculate the 35mm equivalent, you take the focal length range and multiply it by the conversion factor. For example, an 18-55mm lens in a Pentax dSLR would have a 35mm equivalent focal range of 27-82.5mm
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Old Jan 20, 2007, 11:55 PM   #6
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The 18-55 would be equivalent to (in 35mm "equivalent focal length"):

27.0-82.5mm EFL on a Nikon, Sony, or Pentax
28.8-88.0mm EFL on a Canon Rebel
36.0-110.0 EFL on an Olympus or Panasonic "four thirds" camera

In any case it's a range of 3x. A typical 3x point and shoot would be something like the 36-110. The others will provide a bit less tele but a better wide angle.

A "normal" focal length is often consider to be 50mm on 35mm film, but technically, "normal" on any format should be equal to the diameter of the sensor, so really that should be 43mm EFL. Thus, that lens would be considered a "standard zoom" for most of these as it covers a rnage from a good wide angle to a short telephoto (somewhere near 2x normal magnification).

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