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Thread: Small Focal Length Question on Lenses

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    Super Moderator Bryan's Avatar
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    Small Focal Length Question on Lenses

    All,

    This seems like such a dumb question, but I was looking through lenses and it occurred to me: why are lenses sold with relatively small focal length ranges? For example, in the 18-55mm range provided by my D3100's kit lens, I could buy the following from Nikon:


    • 17-35 f/2.8
    • 16-35 f/4
    • 18-35 f/3.5-4.5
    • 16-85 f/3.5-4.5


    I'm certainly not asking for the pluses and minuses of each lens, but I don't understand why there are so many focal length choices in the same range. Yes, I realize that the apertures are different, but why would I want an 18-35 f/3.5-4.5 to supplement my 18-55 f/3.5-5.6, or why would I want two lenses when I could just use one?
    Quote Originally Posted by DazedAndConfused
    I dont know a word you just said, but that **** sounded COOL.

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    STAR Sponsor smaeda's Avatar
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    Unlike prime lenses, where all lens elements can be utilized to maximize the image quality at a single focal length, zoom lenses have to make trade-offs between image quality, focus, and various optical aberrations. Smaller zoom ranges usually tend to have better IQ throughout the focal range, while lenses with larger zoom ranges often have a sweet spot where IQ is at its best, which falls off as you move towards the extremes.

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    Super Moderator Bryan's Avatar
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    That answer makes a lot of sense. I guess I just have a feeling most "people who like taking pictures" like me (I would not currently call myself a photographer ) probably couldn't tell the difference.
    Quote Originally Posted by DazedAndConfused
    I dont know a word you just said, but that **** sounded COOL.

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    STAR Sponsor smaeda's Avatar
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    You would be surprised. Once you start shooting with a decent lens, the IQ difference becomes extremely noticeable. I copied and pasted the above reply by the way. lol.

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    Super Moderator Bryan's Avatar
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    Quote Originally Posted by smaeda View Post
    I copied and pasted the above reply by the way. lol.
    I thought it seemed a little too "by the book"

    So basically it's a matter of IQ going up as the focal range goes down (in general), right? That said, lenses like the 24-70 exist because sometimes you just can't have 5 lenses in your bag at once and expect to catch the moment?
    Quote Originally Posted by DazedAndConfused
    I dont know a word you just said, but that **** sounded COOL.

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    2,000 rpm - light wheelspin, no bog here! roy obanion's Avatar
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    Also different ones are released at different times. Some of those are older lenses and some are newer..and some are DX only (crop sensor), others are FX (full frame compatible)

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    Super Moderator Bryan's Avatar
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    Good point. I didn't think about that.

    Still, I was wondering why you'd have, say, an 11-16 for wide shots. Why do you need such a narrow focal length? It's not like 18-55, 55-200, 24-70, etc. where you're covering from wide to narrow-angle...wouldn't you be better served to just have a prime?
    Quote Originally Posted by DazedAndConfused
    I dont know a word you just said, but that **** sounded COOL.

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