Are primes brighter and sharper than wide open zooms

Discussion in 'Digital SLR' started by Siddhartha Jain, Sep 28, 2005.

  1. Siddhartha Jain

    no_name Guest

    Except when it's not ... like a really well made fast zoom lens being
    compared to a really poorly made slow prime lens.
     
    no_name, Sep 29, 2005
    #41
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  2. Siddhartha Jain

    no_name Guest

    However, a pound of gold and a pound of feathers do not.
     
    no_name, Sep 29, 2005
    #42
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  3. Siddhartha Jain

    W.E. O'Neil Guest

    Strictly speaking you are on the wrong track. I think you may be confusing
    transmission with focal ratio. F2.8 simply speaks to the focal
    ratio.......slower materials would result in less light being transmitted.
     
    W.E. O'Neil, Sep 29, 2005
    #43
  4. Siddhartha Jain

    Peter Guest

    Actually no, but in most cases the difference is unimportant.

    One case where the difference generally is important is with
    a mirror lens. A mirror lens is generally only about 60%
    efficient compared with around 90%+ efficiency for a glass
    lens with ten multicoated air-glass surfaces.

    A 500mm f/6.3 mirror lens may let in about the same light
    as a 500mm f/8 coated glass lens. This can be a significant
    factor when deciding what lens to buy. A mirror lens does
    not gather quite as much light as you would expect from
    the aperture.

    Peter.
     
    Peter, Sep 29, 2005
    #44
  5. Ahem. Notice the previous 50+ responses in this thread? If not, read
    some - you're dead wrong. What you're thinking of is a T-stop. Lenses
    of the same mathematical aperture (f/stop) can and do wary widely in
    transmission. Period.
     
    Scott Schuckert, Sep 29, 2005
    #45
  6. Siddhartha Jain

    Peter Guest


    Actually you are being pedantic, saying "not to be pedantic"
    in front of a sentence doesn't make it so.

    I looked up "slang" and "jargon" in several dictionaries,
    and at least some of the meanings are nearly interchangable.
    I chose "slang" because I wanted to emphasize the non-standard
    nature of the vocabulary rather than any lack of intelligibility
    to outsiders.

    Peter.
     
    Peter, Sep 29, 2005
    #46
  7. I agree with the first part of the above. The only point in which my
    understanding differs is that the traditional use of the term "prime"
    was in the sense of "primary" as opposed to secondary or auxiliary
    optical components such as tele-converters, wide angle attachments,
    close up lenses and the like. Thus prime as in the Latin "primus", first
    or primary.

    This is the interpretation given in the more rigorous works on
    photography I consulted on this issue when the point was debated here
    (ad nauseam) several years ago. (Anyone remember Neil Harrington?)

    David
     
    David Littlewood, Sep 29, 2005
    #47
  8. As it is an ambiguous usage, i.e. one which is in conflict with the
    traditional meaning of the word, then I personally avoid using the word
    altogether. I agree that when others use the word it is usually apparent
    from the context what they mean, but IMO it is mildly rude to one's
    readers to deliberately choose to make them work out meaning from the
    context.

    David
     
    David Littlewood, Sep 29, 2005
    #48
  9. Siddhartha Jain

    Jeremy Guest

    I believe that you are incorrect. the F-stops are geometric measurements of
    the aperture opening. If a lens has a large number of elements, like a zoom
    lens, less light may ultimately reach the film plane (or the chip) than
    would be the case if a lens with a lesser number of elements were
    substituted, even if both lenses were set to the same aperture opening.

    My SMC Takumar 50mm f/1.4 is an interesting example. As is well known, the
    rear element on those lenses had Thorium mixed into the optical glass
    formula, and the decaying atomic particles have yellowed the lens over the
    decades. That lens, set at f/1.4, probably transmits only an amount of
    light equivalent to another (non-yellowed) lens at f/1.8.

    I admit, however, that most lenses, at any given f-stop, probably transmit
    about the same amount of light to the film or chip. But it is not
    absolutely guaranteed. And these days, with TTL metering, the exposure
    values can be adjusted to compensate.
     
    Jeremy, Sep 29, 2005
    #49
  10. Due to the archaic system of weights&measures that uses a different unit
    with the same name for measuring precious metals.

    But a gram of gold and a gram of feathers *are* the same mass, and have
    the same weight in the same gravity.

    Dave
     
    Dave Martindale, Sep 29, 2005
    #50
  11. Siddhartha Jain

    Pete D Guest

    So a Ferrari is faster than a Goggomobile, who'd of thought it??
     
    Pete D, Sep 30, 2005
    #51
  12. Siddhartha Jain

    no_name Guest

    OTOH, "the old question" was weight not mass.
     
    no_name, Sep 30, 2005
    #52
  13. Siddhartha Jain

    Pete D Guest

    IAWCB, I vote to not care what they call non zooms and non fixed lenses! ;-)
     
    Pete D, Sep 30, 2005
    #53
  14. Siddhartha Jain

    Paul J Gans Guest

    I dimly recall the term "prime lens" as being the
    lens whose focal length was equal (at least roughly)
    to the diagonal of the film frame. That made a 50mm
    (or 45mm) lens "prime" for 35mm film.

    A 135mm lens was then a "telephoto" and a 35mm lens
    was a "wideangle".

    Zoom hadn't been invented yet.

    By the way I find acronyms very hard to remember (VHR).
    I much prefer a pronoucible name. Most acronym
    users seem to as well, since they often make the
    acronym pronouncible.

    ---- Paul J. Gans
     
    Paul J Gans, Sep 30, 2005
    #54
  15. Siddhartha Jain

    Peter Guest

    The usual term for this is "normal lens"
    A telephoto lens, properly speaking, is one in which
    the lens (when set to infinity focus) is closer to
    the film/sensor than the focal length of the lens.

    It is quite possible to have a wide angle lens
    which is of telephoto constuction. Olympus compacts
    have had such lenses for years. On an Olympus XA,
    the point 35mm in front of the film is actually
    just in front of the front element of the lens.

    A lens which is significantly longer than a normal
    is called a long-focus lens if it is not of telephoto
    design.

    Wide angle lenses for SLRs are generally of an
    inverted telephoto type in which a point one
    focal length in front of the film may be somewhat
    behind the rear element of the lens.

    Peter.
     
    Peter, Sep 30, 2005
    #55
  16. Siddhartha Jain

    Eugene Guest

    Isn't that what's refered to as a "standard" lens?
     
    Eugene, Sep 30, 2005
    #56
  17. Siddhartha Jain

    Tony Polson Guest



    .... or "standard lens", which is common usage in the UK.
     
    Tony Polson, Sep 30, 2005
    #57
  18. Siddhartha Jain

    Chris Brown Guest

    I know this may give you apoplexy, but my nice shiny EOS 5D which I bought
    yesterday includes, in the box, an accessories catalogue from Canon, which
    amongst other things features a complete list of their current EF lens
    range. They split it up into the following categories (from memory):

    Zoom
    Macro
    Tilt and Shift
    and, yes, Prime, which lists all of their fixed-focal length lenses (apart
    from the Macros and T&S).

    So at least one manufacturer is using the term to mean fixed-focal length.
     
    Chris Brown, Sep 30, 2005
    #58
  19. Siddhartha Jain

    Peter Guest

    I am willing to bet that some (possibly all) of the "macro" lenses
    in the brochure are not really macro lenses intended primarily for
    1:1 and greater magnification.

    I would not be even slightly surprised if the word "telephoto" were
    used more than once in the brochure to describe something that is
    not actually a telephoto lens.

    If you get your terminology from advertising literature, you are
    probably going to get it wrong.

    Peter.
     
    Peter, Sep 30, 2005
    #59
  20. Siddhartha Jain

    Chris Brown Guest

    Actally they are. Canon have lots of lenses with so-called "Macro" zones on
    their focus ring, which aren't actually 1:1, but AFAIK all the lenses in the
    "Macro" category are true 1:1 or greater lenses.
    If you're going to object to the "misuse" of telephoto, you're fighting a
    cause which is even more lost than the "prime" caus. I rather suspect that
    the vast majority of non-LF photographers don't actually even understand
    that it ever had a different meanning to its current one. What woul dyou
    have people call what the whole world and their granny now calls "telephoto"
    lenses? Narrow-angle, perhaps?
    If you want to be prescriptive about language, then you're off to a really
    bad start by chosing English to fight your battle in. Perhaps you'd have
    better luck with Latin?
     
    Chris Brown, Sep 30, 2005
    #60
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