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Thread: SLR lens Zoom factor

  1. #1

    Default SLR lens Zoom factor

    Hi all,

    I was just wondering how powerful the zoom on SLR lens.
    Currently i owned a canon G5 which has 4x optical/ 4x digital zoom.

    If i bought a canon 300d with EF-S 18-55mm lens.

    How powerful the zoom on this lens ? (in term of "Xx optical zoom").

    I can't find this info on the need..

    TIA

    cheers & beers,
    Awie

  2. #2

    Default

    Quote Originally Posted by awie
    Hi all,

    I was just wondering how powerful the zoom on SLR lens.
    Currently i owned a canon G5 which has 4x optical/ 4x digital zoom.

    If i bought a canon 300d with EF-S 18-55mm lens.

    How powerful the zoom on this lens ? (in term of "Xx optical zoom").

    I can't find this info on the need..

    TIA

    cheers & beers,
    Awie
    ==> I can't find this info on the need..
    ==> (correction: on the NET).. :-)

  3. #3

    Default

    Hi... welcome to clubsnap...

    Typical consumer cameras starts the zoom at 35mm.

    Dun be confused with "35mm camera" or "35mm equivalent focal length". The former means that the camera uses a film of size 35mm.(those widely used films.) The latter is more technical. Won't go into that yet.

    So for a normal 35mm camera, with starting focal length at 35mm(widely available type), a 3x zoom camera will have focal length from 35mm to 105mm (note: 105/35 = 3).

    Also note that:
    For a normal 35mm camera, with starting focal length at 28mm(may be a bit more expensive), a 3x zoom camera will have focal length from 28mm to 84mm (note: 84/28 = 3).

    Thus the more professional way of telling pple how much zoom your camera/lens have is to quote the focal length millimetres. Pls note that the larger the number, the "further" you can see.

    For your qn: 18-55mm
    In the case of the Canon 300D, the sensor size is not as large as the normal film(35mm film) everyone uses. it's slightly smaller. Thus if you look at it from another way, the image is actually cropped. That's where the "cropping factor" comes in. The 300D has a cropping factor of 1.6. The cropping factor differs from camera to camera. depending on the sensor/film size.

    Thus when pple say "35mm equivalent focal length", he has already taken the cropping factor into account. So the 35mm equivalent focal length of the EF-S 18-55mm is from 28.8mm to 88mm.( 18x1.6=28.8, 55x1.6=88)

    So in reality, your EF-S 18-55mm only has 3x zoom...


    Another example:
    A 70-200mm lens
    200/70 = 2.86
    Thus, this lens only has 2.86x zoom... But it can "see" further, coz it starts at 70mm, ends at 200mm.
    Last edited by AReality; 4th December 2003 at 03:08 PM.

  4. #4
    Senior Member ivor's Avatar
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    Default

    In simple words, I would say, it is about 3X

    Quote Originally Posted by awie
    Hi all,

    I was just wondering how powerful the zoom on SLR lens.
    Currently i owned a canon G5 which has 4x optical/ 4x digital zoom.

    If i bought a canon 300d with EF-S 18-55mm lens.

    How powerful the zoom on this lens ? (in term of "Xx optical zoom").

    I can't find this info on the need..

    TIA

    cheers & beers,
    Awie

  5. #5
    Deregistered
    Join Date
    Dec 2002
    Location
    Planet Nikon
    Posts
    21,905

    Default

    In my terms... optical zoom is not the determining factor in SLR... it's the focal length that matters

  6. #6

    Default

    Quote Originally Posted by awie
    ==> I can't find this info on the need..
    ==> (correction: on the NET).. :-)
    just search clubsnap.

    http://forums.clubsnap.org/showthread.php?t=52179

    to convert the 18-55 to 'optical zoom', just divide 55 by 18 = 3.1x optical zoom.

  7. #7

    Talking

    Thanks very much all for replying..
    especially AReality for giving such detailed answer.. THX ! :-)

    cheers & beers,
    Awie

  8. #8

    Default

    welcome...

    Enjoy your stay here...

  9. #9

    Default

    Wow amazing! Thanks Gavin for elucidating so well on something that has always puzzled me!

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