Yet another lens question

Discussion in 'Digital SLR' started by Roger, Sep 6, 2006.

  1. Roger

    Roger Guest

    Is there any benefit to a F2.8 lens vs an F4 lens if I don't expect to
    shoot at less than F4?
    The F2.8 is a lot more expensive so is there an increase in image quality
    when both are shot at F4 or more?
    Roger, Sep 6, 2006
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  2. Roger

    Todd H. Guest

    Yes, your F4 shots will gneerally be sharper because lenses always
    show their warts wide open. f/4 on a good f/2.8 lens well, isn't wide

    And are you SURE you'll never wnat to shoot at f/2.8 and get really
    shallow depth of field to really blur out the background? Oh, I bet
    you might. :)
    Generally, yes.
    Todd H., Sep 6, 2006
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  3. Roger

    Bill Guest

    Generally any lenses used wide open aren't as sharp as when they're
    stopped down a notch or two. So the f/2.8 should be a tad sharper when
    you close it down to f/4.

    Once you get into the really good glass though, like the Canon L or
    Nikon Pro lenses, the differences in optical quality wide open is often
    too small to care about.
    That's partly why I bought the Canon 70-200 f/4 L over the bigger and
    heavier f/2.8 version. It's small and light enough to be carried
    relatively easily, and with the Canon 17-40 f/4 L, two lenses cover most
    of what I need in two reasonably priced and sized models.

    The image quality of the f/4 is amazingly good, arguably the equal of
    the f/2.8 model.
    Bill, Sep 6, 2006
  4. Huh? I'm sure there are many Canon and Nikon users that will disagree with
    you, I know I do. I can safely say that I'm pretty much satisfied with the
    optical performance wide-open on all my 2.8s, even my 85mm f/1.4 does an OK
    job wide open. Of course, there might be a few dogs in both lineups, but
    for the most part if there wasn't a noticeable improvement the pros wouldn't
    buy them.

    Rita Ä Berkowitz, Sep 6, 2006
  5. Roger

    Bill Guest

    Which is what I said above.

    Perhaps you misunderstood, but I'm saying the same thing, wide open
    isn't really an issue with good glass.
    Bill, Sep 6, 2006
  6. Roger

    Paul Furman Guest

    Additionally, the 2.8 lens will give you more light in the viewfinder
    for focusing and composing, particularly when autofocusing in low light
    or tough conditions or with a teleconverter.
    Paul Furman, Sep 6, 2006
  7. I think that is what he was saying. The image quality loss due to shooting
    wide open is minimized with high-end glass.
    Thomas T. Veldhouse, Sep 6, 2006
  8. Roger

    Bill Guest

    That's something I think Nikon has an advantage over Canon.

    Comparing my Canon XT to the Nikon D70s, I've found with similar lenses
    the Nikon is much better at focusing in low light. In almost complete
    darkness the Canon hunts, while the Nikon will find and lock focus.

    This is with the focus-assist light disabled. When enabled, both are
    about the same.
    Bill, Sep 6, 2006
  9. Got it. Thanks.
    Yep, I thought you were comparing the f/4 lens to the 2.8s.

    Rita Ä Berkowitz, Sep 6, 2006
  10. I've had mine turned off on all my Nikon bodies. I don't even know why they
    put focus assist on their bodies other than to drain batteries?

    Rita Ä Berkowitz, Sep 6, 2006
  11. Roger

    DoN. Nichols Guest

    There are times when the focus-assist light helps. And there are
    other times when it is a distraction -- especially when you want to
    remain unnoticed while you are taking.

    All in all -- I am glad to have it -- but also glad that it can
    be disabled.

    DoN. Nichols, Sep 7, 2006
  12. Roger

    Aad Guest

    The lens is only stopped down when you actualy take the shot.
    AF and AE are always measured 'wide open'.
    Therefore your AF and AE are faster and more acurate with 'faster' lenses.
    (that's why they're called 'fast')
    Again, particularly in low light situations.
    Aad, Sep 7, 2006
  13. Roger

    Alan Browne Guest

    A lens is usually at its peak sharpness 2 - 3 stops closed from its
    widest aperture, so the f/2.8 lens will have a minor advantage in that,
    er, light.

    Manufacturers tend to "do their best" in the pro (eg: f/2.8) glass v.
    the "very good" glass that they might limit to f/4 for cost reasons.

    The above generalities, however, are imperceptible in most images you
    make. So if the extra shallow DOF is not of need, low light shooting is
    not in the cards (not that 1 stop is all that important, a 1 stop of ISO
    boost will suffice in mose cases) then the less expensive glass will do
    you you good and not be as heavy to carry.

    Alan Browne, Sep 8, 2006
  14. Roger

    AaronW Guest

    You might want to upgrade to f/2.8 zooms later. The new Canon f/4 IS
    zooms are not that much cheaper. They are more for people who want to
    save weight, than for people who want to save money. If money is a
    concern and you don't want to lose too much money when you upgrade to
    f/2.8 zooms, you can also consider f/3.5-5.6 variable aperture zooms
    for now. The new computer designs are much better, e.g., Canon
    70-300/4-5.6 IS, Nikon 55-200/4-5.6, ..., especially if you plan to
    stop down to f/8.
    AaronW, Sep 8, 2006
  15. Roger

    Greg \_\ Guest

    Too bad DOF sucks at 5.6
    Greg \_\, Sep 8, 2006
  16. Roger

    RichA Guest

    Depends what you want. If you want the sharpest image, stopping down
    will provide it. Residual aberrations are lessened. I've never seen
    an MTF diagram that showed any lens wide open matched it's stopped down
    performance. However, if they offer what you want wide open and the
    extra sharpness or contrast is not important, you'd be right.
    RichA, Sep 8, 2006
  17. Depends on the lens focal length ...
    Thomas T. Veldhouse, Sep 8, 2006
  18. Roger

    zeitgeist Guest

    most lenses are better at one stop down than wide open and hit their best at
    2 stops down.

    f/4 lenses tend to be made for the consumer market and are cheaper in more
    than just price.

    you can never be too thin too rich nor have a lens that is too fast.
    actually having that extra stop really means a lot since much of my portrait
    work is window light, twilight and open shade, also with flash and ambient
    light blending where you select an f/stop to control the flash with a slow
    enough shutter speed to allow the ambient light to come up to one stop under
    the key light exposure and WOW, the image gets great depth and detail.
    works great for weddings in churches, the bride isn't a washed out ghost in
    a coal mine.
    zeitgeist, Sep 9, 2006
  19. Roger

    Alan Browne Guest

    Too bad you're not contributing to the discussion, nor carefully reading
    posts that you reply to.
    Alan Browne, Sep 9, 2006
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