Question by For Real: Would someone please explain to me how the Zoom on a camera lens compares to the X power of a rifle scope?
For example I have 4X power rifle scope which means that what I’m looking at through the scope is magnified four times it’s actual size.
How does this work with a zoom lens? Is a 200mm setting three times closer than a 50mm setting?
Is there a formula for figuring this out?

Best answer:

Answer by rs
Zoom on a camera only describes the RANGE of focal lengths of the lens.
So a 4X zoom may be from 25-100mm focal length.
A 35mm film camera was the standard for comparing magnification for most photographers (and often it still is). A 50mm lens approximated the diagonal dimension of the film frame so a 50mm lens is refered to as a “normal” lens. It came the closest to what your eye saw at 1X magnification.
That means a 25-100mm zoom lens has a magnification of 1/2X at its widest setting to 2X at its highest magnification.

Power or “x” factor on a scope is MAGNIFICATION. A 4X scope sees and object as if it were 1/4 the true distance to you.

For your question, a 200mm setting is 4X more magnification than a 50mm setting.

When reading specs on a camera, you have to dig down to get the “35mm” equivalent of the particular camera focal length. An 7-28mm zoom may actually translate to 28-112mm in “35mm equivalent” because the CCD sensor on the camera may be only 12mm diagonal.

Here is your formula:

1. Make sure you find the “35mm equivalent” focal lengths of the lenses
2. Divide by 50mm to get your magnification range.
3. If the camera is 35mm film or is an expensive “full frame” sensor, simply divide by 50mm to get your magnification.

Many DSLR’s tell you the “conversion factor” of lenses. Typical factors are 1.5, 1.7 and 2. That means when you stick a 100mm lens on a camera with a 1.7 conversion factor, the lens is equivalent to a 170mm lens on a 35mm camera and your magnification is 170mm/50mm = 3.4X

Here are some examples of 35mm equivalent focal lengths:
28mm = 0.56X good wide angle. You can capture nearly an entire bedroom view without “fish-eye” distortion
35mm = 0.7X mild wide angle. Easier to get group shots without backing up too much
50mm = 1X Pretty much what your eye sees in terms of magnification
85mm = 1.7X good portrait lens for face shots
200mm = 4X used to be the consumer limits for inexpensive telephoto shots
500mm = 10X used to be top of the line telephoto. These are the lenses used by those pro photographers that often get tackled on the sidelines of football games .

Hope that helps

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