Zoom Measurements in "x" vs. "mm"

Home Forums Photography Q&A Zoom Measurements in "x" vs. "mm"

This topic contains 4 replies, has 4 voices, and was last updated by  Ezra Morley 2 months, 2 weeks ago.

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    Samuel Vanderford

    Hey guys! This is probably a simple question but I have looked around online and haven’t seemed to be able to find the answer. Consumer video cameras in generally tend to use an “x” measurement for their zoom (e.g. “30x zoom!”) while SLR camera lenses use a “mm” measurement for their zoom (e.g. “70-300mm lens”). Does anyone know how to approximately calculate the ratio between these two for comparison purposes?



    Silas Wood

    Silas Wood

    it seems to me that 30x = 27-810mm


    Austin Vinar

    There is no comparison. MM is an exact measurement that remains relatively equal across cameras. X zoom is simply what it sounds like. I have a 150-600mm lens. It is a 4x zoom. Yet a 10-100mm is a 10x zoom. A 10-200mm is a 20x zoom. Simple multiplication. Otherwise I wouldn’t understand it. 🙂

    It also works for marketing. They can advertise a 5-200mm lens as having 40x zoom. Yet you barely have enough to shoot wildlife.

    A prime 800mm lens has 0x zoom, because it doesn’t zoom.

    Let me know if I can explain it farther.



    Ezra Morley

    Austin is right.
    “50X” or any other “x” number is basically just a marketing gimmick for one camera manufacturer to say, “Our camera has more zoom than yours.” In fact, it might have less zoom, depending on how they wiggle the numbers. I was positive I had written on this topic before, but I can’t seem to find it. I did find a post about where I commented about it on the NF Google+ page, so I’ll link to it for further information: https://plus.google.com/109808589691632341353/posts/RuuctZ4yJ9k

    Does anyone know how to approximately calculate the ratio between these two for comparison purposes?

    To answer your question though, the answer is to compare “full-frame equivalent” mm measurements. So while your superzoom says 30X in big bold letters on it, it should also say something like “10mm-300mm equivalent”. Take those numbers and compare them with your DSLR lens, and you’ll get the info you need. Remember that if you’re working with a crop-sensor DSLR that you have to take that into account. So a 300mm lens on a crop sensor Canon camera will be 480mm “full-frame equivalent”.

    Feel free to ask more questions if you’re still not sure what we’re talking about. 🙂

    See here for some additional reading on crop sensor vs. full frame:

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