Good Lens/Bad Lens?

Discussion in 'Digital Photography' started by the_niner_nation, Jun 29, 2007.

  1. I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my
    canon 400d and read a lot of favourable reviews.
    A lot of the reviews, however are very excited about having a 'good copy' of
    this lens.

    As a newbie, i am confused...arn't ** all** these lenses made to the exact
    same specification and manufacturing processes?

    And how can you tell a 'good' copy' of this lens from a 'bad copy' ?
    Just how much *worse* can a bad copy can be from a 'good copy' ?
    And again, I am staggered that there are discrepencies that are pretty
    important on somrthing I believed was manufactured in a mass production
    system..it's not like buying a hand made silk suite etc.
    I am thinking of buying this online, what sort of test can i do with this
    lens to ensure it's a 'good copy' and can I legally return it to the seller
    if it turns out to be a 'bad copy'?

    Thanks in advance!
     
    the_niner_nation, Jun 29, 2007
    #1
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  2. the_niner_nation

    Jim Guest

    Yes, but also there is a tolerance on all dimensions and all glass. So,
    there will be a
    difference between lenses. As none of the manufacturers tell us how close
    their lenses
    come to the specifications, there is no way for us to judge how well a
    particular lens
    will perform without actually using it.

    Jim
     
    Jim, Jun 29, 2007
    #2
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  3. the_niner_nation

    Tony Hwang Guest

    Hi,
    Copying 100% is not a hard thing to do but legal matters.
     
    Tony Hwang, Jun 29, 2007
    #3
  4. the_niner_nation

    Frank Guest

    I'm skeptical to be honest. I have never had a problem with Canon lenses,
    therefore I wonder if maybe it is operator error.

    I do remember reading something recently though (regarding back focus if I
    remember correctly) that says that lenses have a tolerance for 5 for
    example, so it could be anywhere from -5 to +5. The bodies also have a
    similar tolerance. Therefore, it could be possible that if the body was at
    one end of the specification tolerance, and the lens was the other, then
    even both are within spec, they could not be working optimally.

    I can't find the article.
     
    Frank, Jun 29, 2007
    #4
  5. the_niner_nation

    Eatmorepies Guest

    Hello again

    It's true that manufacturing tolerances will produce variation in
    lenses/bodies. Modern manufacturing techniques make those variations quite
    small.

    Canon sell L lenses to the pros. Canon can't afford to have poor build
    quality on L lenses and will not be supplying seconds to eBay sellers. Look
    at the problems they are facing with the current MK III - they have to have
    their pro equipment up to scratch or lose sales.

    John
     
    Eatmorepies, Jun 29, 2007
    #5
  6. In theory, yes - but it is my impression that the manufacturers
    in practice may check relatively few samples, mostly early in
    the production runs - and some lens designs are more difficult
    than others to get right consistently. Even with producers like
    Nikon, that has a generally good reputation both for high image
    quality in the lenses across its line, and for good sample-to-sample
    consistency, small variations are common - and there is the very
    occasional "dud" (for more, see my extensive lens comparisons,
    including multiple samples of the same lens, at:
    www.donferrario.com/ruether/slemn.html ).
    I test using detailed and familiar infinity-distance targets to
    establish that all four corners are equally sharp (or possibly
    unsharp at wide stops...;-), as are opposite sides of the frame
    (with all camera controls locked down) at the widest stop, f5.6,
    and f11. There is more to it than this, but this can get you
    started - but just don't become preoccupied with it(!). For
    digital, adding newspaper targets can be useful if you are not
    shooting too close, since this can show asymmetrical CA problems.
    Have reasonable expectations for the performance of the tested lens
    (which should be very high for the lens you mentioned - it should
    check out as quite sharp in all corners and edges wide open if
    properly focused and the sample is good).
    With some lenses, very much worse. For instance, many people
    like the Nikkor 35-200mm f3.5-4.5 MF, but two samples I had
    were very soft. Nikon's 35-105mm f3.5-4.5 MF also varied,
    but not quite so much (from so-so to superb) - but these were
    the only two Nikkors I found much sample variation with. In other
    brands, I have seen many more...
    This is why I ALWAYS recommend that new gear be checked
    IMMEDIATELY! I'm amazed when pro acquaintances buy gear,
    don't bother to check it out, then later discover the problems when
    it is too late for an exchange/refund. I've found that warranties on
    lenses are nearly useless - repair people often cannot correct lens
    manufacturing faults (just possibly the damage from accidents).
    See above - but establish in advance the seller's return/exchange
    policy. (BTW, I like dealing with the no-nonsense people at
    B&H Photo (www.bhphotovideo.com). Just don't expect them to
    hold your hand...;-)
     
    David Ruether, Jun 29, 2007
    #6
  7. the_niner_nation

    Chuck Olson Guest

    Others have addressed the lens testing and production tolerance issues of
    your long lens. Going to L-Class, I feel, is the best you can do to minimize
    the likelihood your lens will not perform as you want it to. Even more
    important than getting the L-class would be Image Stabilization. When You
    buy a lens that has excellent sharpness, you need every trick you can muster
    to make sure that its great sharpness will be present in your final images.
    The IS, IMHO is a must-have for any long lens. The sharper the lens, the
    more important is Image Stabilization.
     
    Chuck Olson, Jun 29, 2007
    #7
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