The definition of "bad copy"?

Discussion in 'Nikon' started by mike k, Jul 11, 2014.

  1. I've read a lot about "bad copy" and various articles, and I know people generally don't like reading questions about it, but I've just received a 2.8 zoom lens, and the lens at 2.8 is so bad I cannot use it.
    I tested it on various lighting condition, and found that at f/2.8 it's so soft and blurry its really unusable under almost all conditions. However, as soon as I stop it down to f/4, it is very sharp.
    I've compared my image to the sample image on the internet, and found that my lens is more blurry (both at f/2.8). But at f/4, it's excellent, no problem at all. I'm perplexed because I don't know if I should keep it. If I do, I won't be using it at f/2.8.
    What constitute a "bad copy"? If it's sharp at some stopped-down apertures, is it by definition not a bad copy? If it is "bad", is it bad at all aperture? Or is it possible for some defects to affect only at the widest aperture?
    Thanks.
     
  2. What lens is it?
     
  3. Or is it possible for some defects to affect only at the widest aperture?​
    Yes, but it would be rare. It's extremely common for a lot of defects to become less noticeable as you stop down, however.

    Assuming you wanted to use the lens at f/2.8 and that's why you paid for it, I'd think twice before keeping it. But it would be helpful to know what the lens was, as Andy says. For example, I find the 80-200 AF-D unusably soft at f/2.8 and shortish distances, particularly at 200mm. It's very good at longer distances and much better stopped down.
     
  4. ShunCheung

    ShunCheung Administrator

    Yeah, which f2.8 zoom is this lens; i.e. what is the focal length range and is it Nikon or third party? Did you buy it new or it is used?
    If it is sharp at f4, most likely it is not some lens element decenter issue. It may help if you can post some image samples.
     
  5. Read this blog post. Lens QC varies a lot among manufacturers, though Zeiss is a bit more consistent at producing good lenses than Canon and Nikon.
    http://www.lensrentals.com/blog/2013/09/there-is-no-perfect-lens
     
  6. Bad copy would mean that for a model of the lens almost all of them are good but the bad copy is significantly worse. If most of them are bad then it's not bad copy but rather bad model.
     
  7. Are you using autofocus? Are you certain that your camera is focusing correctly? Try focusing in live view for comparison.

    I recently bought a very sharp lens. But before I did a micro fine tuning adjustment, it produced blurry images wide open.
     
  8. ". . . so bad I cannot use it."​
    I think you just answered your own question.
    It is a prime? If not, does it have constant aperture f/2.8 throughout the focal range, and is it consistently bad throughout the focal range?
    --Lannie
     
  9. I find the 80-200 AF-D unusably soft at f/2.8 and shortish distances, particularly at 200mm​
    IMO no lens performs on the same level at all apertures and distances. Therefore its wise to know about that characteristics and use the right lens for the job.
     
  10. Bad copy has no definition, it is internet-speak for "I am unhappy with my gear", too often without any context whether whoever uses it, is actually knowledgable on how it ought to work. In the background, of course there are lemons and minor product variations. It sure happens. Not as much as internet forums may make you believe, but there is no 100% perfect production process anywhere. So, in between production failure and user error, somewhere, there is 'bad copy'.
    In other words, the internet isn't always as great a source as it may seem - a lot of bold claims, too often without any support data. Your lens has its own unique problems, worth looking into. All the noise on the internet - let that go. Do your tests, with your copy, and if it doesn't work as you feel it should, return to the store and see how to resolve it.
     
  11. Most of the above,
    without more information about what the lens is, it's impossible to say whether it's a bad example or maybe even the best of its breed.
    Moreover, "too soft" is also relative. The earliest zoom lenses, like Nader's Corvair, were likely to be unsharp by the most critical standards at "any speed".
     
  12. ShunCheung

    ShunCheung Administrator

    In other words, the internet isn't always as great a source as it may seem - a lot of bold claims, too often without any support data. Your lens has its own unique problems, worth looking into. All the noise on the internet - let that go.​
    Very well said.
    One main problem with the internet is that there is essentially no penalty for being totally wrong. For example, if you invest carelessly in the stock market and you are mostly wrong, big time, you'll lose your shirt and go bankrupt in a hurry.
    On the internet, it is a totally different story. There is no penalty. Instead, bold and outrageous claims gain you fame and publicity. If you are wrong, just come back and make another around of outrageous claims, and then another round ....
    If you suspect that there is something wrong with your lens, you need to make some A/B comparisons with another sample of that same model, or at least a similar lens. Capture some static subjects on a tripod under good sunlight; use live view to fine tune your focus. Unless it is a macro lens, do not use subjects that are within a meter (below 3 feet) to evaluate sharpness. If it is a Nikon brand lens, pretty much all Nikon f2.8 zooms are very high-quality lenses unless it has been abused or is defective.
    P.S. The OP made it clear that it is an f2.8 zoom:
    I've just received a 2.8 zoom lens​
     
  13. Thanks guys for the insightful comments. I intentionally leave out the lens model because I wanted to remain objective and learn the subject. This knowledge will be applicable to other lenses as well. That said, the lens I just purchased is the Tokina 16-28 f/2.8, and use it on a Nikon D800.
    I'll do some extra test shots and evaluate it further. I noticed that it does have some front/back focus issues. But I can't yet pinpoint a correct AF fine tune value to correct it at all focal length and distances.
     
  14. ShunCheung

    ShunCheung Administrator

    Hi Mike, I have no personal experience with that Tokina lens. However, one of the more reliable review sites is PhotoZone: http://www.photozone.de/nikon_ff/594-tokina162828ff
    This is what they have to say about that lens, tested on a 24MP D3X:
    Its primary weakness is corner softness at f/2.8. However, the center quality is great and the borders are generally sharp as well. The corners start to catch up at f/4 and they're very good at f/8.​
    I wouldn't expect a super-wide lens to be great at 16mm, f2.8 on the demanding D800 if you pixel peep.
     
  15. To reiterate - try shooting in Live View, which uses a different type of autofocus (contrast detection). Even if the lens is out of adjustment with your camera, contrast detection autofocus will still work properly. If the camera is tripod mounted and he image is still soft, then I would conclude that the lens has an issue.
    Personally, I wouldn't use third-party zooms with a D800, but it you already own the lens, you might as well try to get the best out of it.
     
  16. I think there are two definitions:
    (1) I have a genuinely bad example of this lens, possibly because the manufacturer's QC is too lax, but probably because someone dropped it before I got it.
    (2) I have a typical example of this lens, but it doesn't live up to the hype on KR's site, or my rigorous handheld testing at 1/30s with an uncoated UV filter suggests it isn't 'critically sharp'.
     
  17. ShunCheung

    ShunCheung Administrator

    Mike, since we are talking about a super wide f2.8 zoom on the D800, you might want to take a look at my experience with Nikon's own 17-35mm/f2.8 AF-S, which is an older lens introduced back in 1999.
     
  18. The DxO measurements seem to follow your tests..
    http://www.dxomark.com/Lenses/Tokina/AT-X16-28-F2.8-PRO-FX-Nikon-mounted-on-Nikon-D800---Measurements__792
    and here...
    http://www.dxomark.com/Lenses/Compare/Side-by-side/(lens1)/370/(lens2)/221/(brand1)/Tokina/(camera1)/441/(brand2)/Nikkor/(camera2)/441
    .........sums up Shun's 'experiences'!
    £410 v £1200............enough said..:)
     
  19. (1) I have a genuinely bad example of this lens, possibly because the manufacturer's QC is too lax, but probably because someone dropped it before I got it.
    (2) I have a typical example of this lens, but it doesn't live up to the hype on KR's site, or my rigorous handheld testing at 1/30s with an uncoated UV filter suggests it isn't 'critically sharp'.​
    They way I think about bad copy I think only half of your #1 definition fit. That is it's a bad example of the lens due to manufacturing defects. If it's dropped then it's a damaged copy. If all or most of the lenses of the model are not up to your expectation then it's just a bad lens model and not bad copy.
     

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