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Thread: Difference between focal length multiplier and crop factor

  1. #1

    Default Difference between focal length multiplier and crop factor

    Hi all,

    Is there a difference between focal length multiplier and crop factor?
    I know most DSLRs have a crop factor of 1.6-1.7, whereby the CCD is smaller and the focal length has to be multiplied by the crop factor to get the actual focal length.

    For olympus, using 4/3 technology, the actual focal length of a 14-45mm kit lens is actually 28-90mm with a focal length multiplier of 2.

    So, is there any difference between the 2 terms?

  2. #2

    Default Re: Difference between focal length multiplier and crop factor


  3. #3
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    Default Re: Difference between focal length multiplier and crop factor

    Quote Originally Posted by yzr500abe
    Is there a difference between focal length multiplier and crop factor?
    Yes. Focal length is a property of the lens. "Crop factor" refers to the size of the sensor.

    I know most DSLRs have a crop factor of 1.6-1.7, whereby the CCD is smaller and the focal length has to be multiplied by the crop factor to get the actual focal length.
    No, you don't multiply to "get the focal length". The focal length does not depend on the sensor.

    the actual focal length of a 14-45mm kit lens is actually 28-90mm with a focal length multiplier of 2.
    No, the actual focal length of a 14-45mm kit lens is 14-45mm.

  4. #4

    Default Re: Difference between focal length multiplier and crop factor

    Quote Originally Posted by Imaging-resource.com
    The kit lens is a 14-45mm lens, which is equivalent to a 28 - 90mm lens on a 35mm camera, due to the 2x multiplication factor that must be applied. Though they offer a lens that will take you out to a 14mm equivalent, it costs around $2,600, too much for consumers. Another option takes you out to 22mm equivalent (the 11-22mm f/2.8 Wide Zoom), but that's also around $950 SRP. For the record, wide angle is the biggest problem for modern consumer SLRs and is not unique to the Olympus line.
    I've got the above quote from Imaging resource user review article on e-500
    http://www.imaging-resource.com/PRODS/EV500/E500A.HTM

    so the multiplier only applies if i put in a lens mean for 35mm or the 14-45mm lens on 4/3rd sys is the equivalant to 28-90mm on 35mm.

  5. #5
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    Default Re: Difference between focal length multiplier and crop factor

    It's the field of view equivalent, not focal length equivalent.

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    Default Re: Difference between focal length multiplier and crop factor

    Quote Originally Posted by yzr500abe
    I've got the above quote from Imaging resource user review article on e-500
    http://www.imaging-resource.com/PRODS/EV500/E500A.HTM

    so the multiplier only applies if i put in a lens mean for 35mm or the 14-45mm lens on 4/3rd sys is the equivalant to 28-90mm on 35mm.
    The link you provide doesn't say that the focal length would change. It talks about an "equivalent focal length", which is a purely fictitious quantity. (And it's not really equivalent either).

    A consistent and valid criterion to compare lenses for different image formats is not focal length, but the angle of view (typically given across the diagonal of the image frame).

    The vast majority of information on the web is crap. You have to sift through the rubble to find some gems. If things don't seem to make sense, it's frequently because they're wrong.
    Last edited by LittleWolf; 22nd October 2005 at 11:49 PM.

  7. #7

    Default Re: Difference between focal length multiplier and crop factor

    Many photographers and websites, when mentioning equivalent focal lengths, actually base their figures on 35mm film format.

    For example, a focal length of 8mm on a digital camera A has a 35mm equivalent focal length of 30mm, meaning that a picture taken using a focal length of 8mm on that camera would have the same angle of view (diagonal) as a picture taken using a 30mm lens by a 35mm format camera. From what I understand, the field of view is measured horizontally, but the aspect ratios of CCD/CMOs sensors varies, so the diagonal angle of view is used instead.

    For DSLRs using a sensor which size is smaller than the 35mm film format, the same applies. So in fact, equivalent focal length and equivalent angle of view actually point to the same issue. It's just that the base reference is 35mm film format as it's so commonly known, understood and used previously.

  8. #8
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    Default Re: Difference between focal length multiplier and crop factor

    difference between crop factor and focal length multiplyer is...

    the difference between: 1/10 and 1 x 0.1
    sigh.

  9. #9

    Default Re: Difference between focal length multiplier and crop factor

    "Focal length multipler" is a marketing term devised by the DSLR manufacturers to trick consumers thinking that their lens will have their focal length extended when mounted on a < 35mm frame DSLR.

    The only way to optically extend a lens' focal length is the use a teleconvertor (usually comes in factors of 1.4x and 2x from the lens manufacturer).

    So, when you read "focal length multipler" applied to a DSLR description, read as the camera's crop factor.

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