Fred Miranda Offline Admin Upload & Sell: On
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stevei wrote:
I'm starting to understand that the hard part isn't testing a lens, it's trying to estimate what percentage of lenses sold are better than the one you've just tested. I.e. they're pretty much all imperfect to some extent, so you've got two things to try to work out:
1. Where does the lens you've just tested sit in the range of all lenses that leave the factory? Is it in the worst 10%, the best 50%, the best 20% etc. As far as I can tell, it's extremely hard to estimate this, though we can perhaps get some idea by sharing test shots on a forum such as this one.
2. What standard of lens is it reasonable to expect? Is it reasonable to return lenses until you get a "best 50%" copy? Until you get a "best 10%" copy?
Then you've got the added problem of lenses having different defects. I've had 3 35/2.8s, and the sharpest one was the most decentered. So now, if I get a lens that is very sharp, I'm more inclined to forgive minor defects in other aspects, as I know that if I get another one without those minor defects, it might be less sharp over most of the frame. Would you rather have a decentered lens that is super sharp except for one less sharp corner, or a perfectly centered lens where every corner is only as good as the weakest corner of the decentered lens?
You can tell I've just bought an imperfect Batis 18 and am trying to decide whether exchanging it is likely to make things better or worse............Show more →
That makes sense Steve and we also have to keep in mind what a specific lens will be used for. For example: If it's a landscape lens, I would prefer having it centered but if it's a lens mostly used for events or portraits, priorities will change. As you wrote, there is tolerance and therefore no perfect copy. Even if you are lucky to get the best of the bunch, I doubt it would make a noticeable difference.
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