Truth about zoom and magnification

When I purchased my Canon K2, I got 28-90mm lens as the kit lens. One of my friend asked me what is the zoom factor, I said its 3x, he proudly claimed that he has a very normal digicam with 30x zoom, that gives 10 times magnification of my SLR. I didn't want to spoil his enthusiasm so said "wow!" and stopped. Here is the truth about zoom and magnification.

There are two types of zooms - optical and digital. Digital zoom is very much like the zoom in your favourite photo viewing software. You can keep on zooming it, but more the zoom, less the clarity. But optical zoom is different. No matter how much zoom you do, it should have the same clarity. If your camera says 30x or even 100x zoom, beware. The optical zoom would be only 5x and the digital zoom factor will be 6x or 20x. The zoom of your digital camera is usually calculated as optical zoom * digital zoom.

Optical zoom factor of a camera/lens is the ratio between its longest and shortest focal lengths. My kit lens is 28-90 mm , makes a zoom factor of 3x. On the other hand, the newly introduced PowerShot a710 has 5.8-34.8mm, making it 6x zoom. Does that means it can magnify twice than my lens? No! If you are thinking that zoom factor defines the magnification, think again. Because the magnification has nothing to do with the zoom factor. Interestingly, 5x optical zoom in one camera may give thrice the magnification as the 5x optical zoom of some other camera!

Normal view of our eyes is equivalent to 48mm (roughly 50 mm). So if a lens says 100mm, that means it can magnify twice than your eyes can see, 200 mm is 4 times and so on. So the magnification factor of my lens would be ~2x and for the a710 it would be less than 1x. Forget magnification, it doesn't provide you even the normal view, its a wide angle lens!

If you are going to purchase a camera don't fall for the "100x zoom"or the "10x optical zoom" factor, look for the magnification factor. It would be less than 2x magnification. Decide wisely :-)

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  1. Hanish Says:

    Wow!!!!!!! and This depicts a real expression unlike when you said "WOW!!!".
    Though I am not passianote about photography, infact, I can hardly appreciate differencr between good one and bad one untill difference is obvious; but this time I could appericiate, not the difference (apart from the difference that you were closer to target as len's focal length increases ) between pics you shot with diff lenses, though almost all of them are really good, but the anthusiasm you have for photography and the info about ZOOM and MAGNIFICATION etc you have. Amazing!!!

    Still one doubt (As Always) that is :
    Though its clear that magnification is one criteria to go for but does optical zoom not matter even??? I mean say if one has a focal length of 100-150 means magnification of 2-3 and optical zoom of 1.5, on other hand one has a focal length of 50-150 means magnification of 1-3 and optical zoom of 3. I guess second one should be better and that means optical zoom is also one of the criteria to go for. what say???

  2. Prakash G.R. Says:

    In 100-150 and 50-150, the maximum magnification is the same, but the minimal differs, so the zoom also varies. In essence, if you are shooting a distant object, both lenses provide no more than 3x magnification, but for shooting pictures of near by objects, 50-150 is better because you can shoot as in near-normal eye view (50mm), but the other one's minimal magnification is 2x, so you have to go little far away from the object to cover the full object