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Thread: plethora of focal length related questions

  1. #1
    Join Date
    Jul 2008
    western europe

    Red face plethora of focal length related questions

    Good day. I promise this will be my last dumb post with silly questions untill
    the winter. Until then i'll try contribute positively.

    I have been trying to learn a few bits about
    Focal length, which confuses the hell out of me. I have established
    that for 35mm-format camera's (the film ones, i guess), a focal length of
    50mm is the "normal" view. Like our eyes. Everything smaller is
    considered wideview, and everything higher is telephoto.

    Now for example, the lens, Konica Kiron 50-200mm 4.5 (fictional example)
    assuming this lens is built for a 35mm format camera, it means the camera
    would have a focal length of 50 to 200, meaning normal view untill 4X the
    distance of normal view.

    Question 1]

    Does it mean it has "4X zoom" ? (basically: means it can focus on an
    object 4 times farther than the 50mm (normal view) view ?

    Question 2] camera in question:

    My little digicam (with video option) has this written on the rim of the
    lens: zoom 6.5-18mm (6x zoom). Since I suspect its lens has a way lower
    focal length number because it doesnt follow the 35mm format camera, how
    can I establish how it compares with the Konica Kiron 50-200mm 4.5 MC (which is substantially
    larger, physically)

    Question 3] (Only applicable if question 1 is correct)

    If a lens with focal length of 200mm (35mm system standard) is basically 4x zoom,
    and my little digicam of above really has 6X zoom, Would anyone preffer a 1970's camera
    with said 200mm lens or above digicam to record/snap any action from
    70 meter/230ft distance ?
    Last edited by angelomcm; 07-29-2008 at 07:45 AM.

  2. #2



    I'll have a go at answering your questions:

    1. Yes the zoom level (i.e. 4x etc) corresponds to the focal length. so 50-200 is x4, 35-105 is x3, etc.

    2. As your object sensor (ccd in your little camera, 35mm film in the case of a traditional film camera) gets smaller - and in the case of your samsung, I suspect it's tiny - well under a cm across, the lens gets closer so the focal length in mm gets smaller for a given magnification.

    Without knowing the object sensor size I don't know the exact correspondence, but usually these compact digicams go from medium wide angle to medium telephoto. So if we assume that the medium wide angle (6.5) is equivalent to around 35, then 18 will be equivalent to around 96. (Which by the way is just short of 3x zoom not 6 times - are you sure you're not counting digital zoom too?)

    3. 230ft is a long way off to snap any action, and a 3x zoom is not really going to cut it... people will still look tiny in the frame. And if you go for a camera with a bigger zoom then you get into issues of camera shake and blurring, because long zooms are hard to hold steady - them magnify movement too!!! To make matters worse these 'super-zooms' being advertised now stop down the aperture so much on the extreme of the zoom that the exposure is usually on the limit (or beyond it) of what you can hand-hold.

    I used to photograph a lot of racing cars and had a 300mm telephoto you had to mount on a monopod to hold steady. By the way it cost more than my camera!

    All the above is written from the POV of still photography, but it all applies to video too for the most part.

    Hope this helps

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