Some Very Basic Questions...

Discussion in 'Digital Photography' started by Ben, Sep 19, 2004.

  1. Ben

    Ben Guest

    Hi there, as you may have guessed from the thread title, i am new at
    SLR photography, but i would very much like to get into it.
    But first i have a couple of questions:
    Is there anywhere on the www, or a book, that could explain to me the
    most basic of things, such as when a lens is described as being 18-55
    mm, what does this measurement actually refer to?
    Also, i would like to choose a lens for my D SLR body (Canon EOS), but
    have no idea which one to pick. Aside from giving me all of the fancy
    specs, most sites i come across do not actually explain things in a
    way that is easy for a COMPLETE beginner to understand. To start off
    with i would like a lens that is good for taking day to day shots, i
    suppose a middle of the road, best of both worlds lens that will help
    me to get used to taking regular kinds of shots.
    I would very much appreciate it if anyone could get back to me to give
    me a pointer in the right direction here.
    Many thanks, Ben.
    Ben, Sep 19, 2004
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  2. Ben

    GT40 Guest might help you. The is some good info on the Canon
    website. For ultra basic info try, www.howstuffworks,com

    For your lens the Canon 28-135mm lens would be a good choice.
    GT40, Sep 19, 2004
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  3. I can't unfortunately point to a good book; I don't have fond memories
    of any one book that really taught me this stuff, and if I did it
    would be outdated and out of print by now. I hope somebody comes
    through on this one for you, because that's the right question to ask!

    The "18-55mm" means that lens is a "zoom" lens (probably technically a
    varifocal rather than a zoom, but almost nobody cares about that
    distinction any more), and it can be set for any "focal length"
    between 18mm and 55mm. The "focal length" of a lens is the distance
    in back of "the lens" (technically one specific one of the "nodal points" of
    the lens but my optics doesn't go that far; for practical purposes
    about the middle of most camera lenses) at which an image of something
    "at infinity" in front of the lens will be brought into sharp focus.

    In *practice* what the focal length means is the angle of view of the
    lens. Smaller numbers mean wider angle of view. Note that the angle
    of view isn't *just* a property of the lens; it's a property of the
    combination of the lens, and the film or sensor it's placed in front
    of. The lens projects a circular image, which the sensor crops to a
    rectangle of some particular shape. The size of the circular image
    (or, often, the lower quality of the outer edges) set a practical
    limit on how big a sensor/piece of film you can use that lens to take
    a photo onto. This is why you need a *different* 200mm lens for a
    35mm camera than you do for a 4x5 view camera; the one made for a 35mm
    camera projects far too small an image to cover a 4x5 sheet of film.
    And why the two lenses of the same focal have different angles of view
    *when used on their intended format film*.

    Kinda by convention, kinda by observation of how the human eye works,
    a focal length about equal to the diagonal of the film (or sensor) is
    considered "normal". For 35mm film, a 50mm lens is considered
    normal. For a 1.6x crop factor digital SLR a 30mm lens would be
    about "normal" in the same sense.

    So that 18-55mm zoom lens would be a pretty good choice for a
    "most-of-the-time" lens on the EOS 300 -- it'd give you coverage from
    moderate wideangle to mild telephoto. Which is why that lens was
    introduced. Like most cheaper zooms, it's fairly "slow" -- low
    light-gathering power, so not too good for shooting in low light
    without flash. Fast lenses are expensive, large, and heavy; like most
    of life, photography is full of tradeoffs.
    David Dyer-Bennet, Sep 19, 2004
  4. Ben

    Tony Morgan Guest

    In message <>, David Dyer-Bennet
    In simple terms:

    focal length = (OD x IS) / OS where

    OD = Object Distance
    IS = Image Size
    OS = Object Size

    So if you have a 1m subject 20m from your camera, and that object gives
    an image size on the CCD of 2mm, then the focal length is 40mm.

    Tony Morgan, Sep 20, 2004
  5. Ben

    Frank ess Guest

    If the OP is interested in a photography primer that includes some of
    the best photographs you'll ever see, look for a set of The Time Life
    Library of Photography. Years old (20?), the principles are current, and
    the underlying educational experience valuable.

    Numerous sets and individual volumes on eBay at any juncture, e.g.:
    Frank ess, Sep 20, 2004
  6. Ben

    Tony Morgan Guest

    Try Shoot Like a Pro! Digital Photography ISBN 0-07-222949-7 and
    Digital Photography Hacks ISBN 0-596-00666-7

    If you're without scruples, you can find these on E-Mule as PDFs.
    Tony Morgan, Sep 20, 2004
  7. I've got that; my parents got it for me fairly early in my career.
    Even then, I found it was fairly superficial, and didn't go into much
    detail about anything. But it *is* filled with very fine pictures,
    superbly reproduced, and that's worth a fair amount.
    David Dyer-Bennet, Sep 20, 2004
  8. Ben

    Matt Ion Guest

    All these questions and more have been asked in this group regularly.
    Try going to and doing a search - they have pretty
    much everything archived back to the beginning of Usenet.
    Matt Ion, Sep 21, 2004
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