The Truth About The “X” Optical Zoom

If you own or intend to buy a digital camera this article is a must read!

One of the most important things people consider before buying a digital camera is the amount of zoom the lens are capable of. Well, you will be surprised to know that the more is not necessary the better. The common knowledge is that the more “X” zoom you have, the bigger the image appears in your camera LCD or viewfinder. Most buyers think that 12X is way better than 3X and this is so just because the marketing campaigns of the camera manufacturers tell them so.

In order to explain what the “X” optical zoom really means it is necessary to explain a few concepts. The “focal length” of a lens determines the angle of view and the size of the image compared to that of the object. Early camera lenses had a fixed focal length dividing them into three main categories: wide-angle lenses, normal lenses and telephoto lenses. From left to right, the focal length is longer for each lens. For easy understanding, your old 35mm film camera that you used to take in your holidays, had a wide-angle lens that allowed you to photograph vast landscapes or to fit your entire family in one single frame. A telephoto lens is the one that sport and safari photographers use to capture details from a considerable distance.

Later, appeared the modern zoom lens which had practically a variable focal length and allowed the photographer to modify it according to its needs. Recently, the marketing campaigns of the camera manufacturers, have come up with a new concept: 3X, 4X, 12X, etc. optical zoom, which had a tremendous success to the public. The rush for optical zoom has driven many buyers in the search for the highest number of “X”s.

But what is the real meaning of the “X” optical zoom? The explanation is quite simple. Focal length is measured in millimeters (mm) and the lowest the number is, the wider is the angle of the lens. As zoom lenses have variable focal lengths, two numbers are used to characterize them. These numbers consist of the lowest and the highest focal lengths the lens is capable of. For example, a 17-40 mm lens is capable of providing all the focal lengths between 17 and 40 mm.

The commercial concept of optical zoom is referring to the fraction between the maximum and the minimum focal length of the same lens. Having said that, it’s obvious that the 17-40 mm lens has an approximate 2,3X optical zoom (40 divided by 17 equals 2,35294118). It’s that simple.

Let’s say, you have a 18-200 mm zoom lens. Now, that we know the formula, we can easily calculate that the lens has a approximate 200/18 = 11X optical zoom. You probably think that you can get pretty close to the action. But what if I’ll tell you that some of that huge telephoto lenses that professional photographers use to photograph subjects on the other end on the football filed have no more than 1X optical zoom? That’s right! A 600mm telephoto lens has the same minimum and maximum focal length so the calculations will look like this: 600/600 = 1X optical zoom. Also, a 100-400mm zoom lens has only a 4x optical zoom although it can bring the image much closer than the 18-200 mm lens.

After reading this, you can now be sure that the “X” optical zoom is no more than the zoom factor of the lens, and has nothing to do with magnification factor of the lens. Still, you may say that having a lens with a high zoom factor, is still a positive aspect as it provides more versatility. That’s also not entirely true. Although it provides versatility, a zoom lens has a lower image quality than a fixed focal length lens. The zoom range is limited by manufacturing constraints; the ideal of a lens of large maximum aperture which will zoom from extreme wide-angle to extreme telephoto is not attainable. Compromises are being made in order to produce lenses with high zoom ranges, but those compromises affect the image quality.

As a conclusion, the “X” optical zoom is not what most people think it is and the bigger is the number in front of the “X” on the case of your camera, the more will suffer the final image that passes through your lens.

The Canon 18-55 f/3.5-5.6 USM lens

3X optical zoom

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The Canon 600mm f/4L IS USM lens

1X optical zoom

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7 thoughts on “The Truth About The “X” Optical Zoom

  1. marc-andré breton

    Thanks for the explanation, you are the first to be able to lighten me up about this subject, i bought an olympus e-500, the seller told me that my lenses were 3.2X and the other 3.8X without being able to tell me why. thanks again

  2. Adrian Flucuş Post author

    You are most welcomed. I am happy that you found this useful. Unfortunately, there are other concepts out there that marketing campaigns distort to their interests. Make sure you pass this link to your friends, so more people will now what they spend their money on, when they buy a digital camera.

  3. shaheen

    your article is informative but does not tell the complete picture. the x factor in DSLRs is necessary to capture details of a distant object. the higher the optical zooming capability the more the versatile the lens is. the image quality may be lower than a fixed focal length lens but it is quite acceptable when it comes to printing large sizes or at times of cropping. however the same cannot be said for point and shoot compact digital cameras.

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