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I am going to be getting a Nikon D7000 soon. I think I'm correct in assuming that the Nikon D7000 will use its own focus motor for an AF lens, but allow the lens to use its motor for an AF-S lens. I'm looking at 50mm prime lenses that are AF and AF-S. From what I understand, AF-S lenses are a bit faster, and possibly more accurate (are they?) but is it worth the extra bump in money (~$85) to go with the the AF-S vs. the AF? How does this question change at other lengths (35mm, 80mm etc.)? Is the answer the same across the board? (If the AF-S simply performs better, I think it's worth the money.)

Does it make sense to go with AF-S lenses now just in case I move to a Nikon DSLR that doesn't have an internal motor?

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3 Answers 3

up vote 6 down vote accepted

Yes, yes, no, maybe, no, probably, no

  • You will have AF focus for both AF and AF-S lenses.
  • AF-S are said to be faster, by how much depends on the lens.
  • They are not more accurate.
  • They may worth it, that depends on your budget and your subject's movements.
  • Probably these differences are the same based on focal-length.
  • A movement from a high-end DSLR to a low-end one is unlikely, unless you want a backup body and cannot afford two high-end ones. It may drive you crazy though!

PS: We recommend one question at a time.

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Except of course that the pro DSLRs don't have AF motors in the body, and they're hardly low-end ;) –  Cry Havok Jul 20 '11 at 20:37
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@Cry Havok - What Nikon pro body doesn't have an in body motor? –  rfusca Jul 20 '11 at 20:55
    
As @rfusca mentions in his answer, AF-S lenses are a heck of a lot quieter than AF lenses. If you ever want to use your 50 at a wedding ceremony or golf game or something else quiet, I'd suggest going for the AF-S. –  Evan Krall Jul 21 '11 at 7:36
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@rfuscs, Cry Havok: the only Nikon bodies without in-body motors are the lowest spec'd consumer bodies. –  jwenting Jul 21 '11 at 13:30
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Logic inversion fault on my part - what I get for posting when half asleep :( Feel free to apply appropriate ridicule ;) –  Cry Havok Jul 27 '11 at 16:07

AF-S are better in nearly every way. Faster and quieter. Accuracy won't be determined by the motor but more so by the autofocus points and system of the camera. The answer is generally the same at every focal length.

Entry level cameras (D3000,D3100,D5000,D5100) are currently the cameras without AF motors in body, so its unlikely you'll be moving to a body without it.

Generally, if you can afford the AF-S lens, it'll be a newer, better overall lens.

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wrong as a generic answer. AF-S lenses are generally the more highend lenses, true. But that's not true for the entry level lenses sold for those low end bodies. Their older AF-D alternatives are superior mechanically and optically as those had to be sacrificed to keep the price of the low-end AF-S lenses acceptable to the customers for those bodies. At the high end, I'd rather have (for most purposes) no AF-S as it adds a lot of weight and for what I shoot the AF speed is mostly irrelevant (lakes and buildings don't run away...). –  jwenting Jul 21 '11 at 13:33
    
@jwentig - Which lens has an AF and AF-S counterpart where the AF-S lens isn't better? –  rfusca Jul 21 '11 at 13:41
    
It used to be only entry level without AF motor; the lack of motor has crept up to intermediate hobbyist level (D5000 and D5100) –  Imre Jul 21 '11 at 19:01
    
@Imre - I knew about the 5000 series, I guess in my mind I was still lumping them into more of like a 'intermediate entry' level ;) since they still lack most external controls. –  rfusca Jul 21 '11 at 19:10
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@jwentig - The 50mm 1.8 af-s is 1 oz heavier (thats how much a single normal slice of bread weighs...) and slightly larger (its difficult to get actual measurements, but visually it doesn't look like much) than the AF D version . Most reviews make special note to point out that overall the optics are improved on the af-s vs the af. The AF-s even now has rounded aperture blades and an aspherical element. Some reviews even point out that the rear of the lens is even sealed now. It's the better lens... –  rfusca Jul 22 '11 at 13:08

I'd say AF-S is a safer bet in the long run. It has been 8 years since Nikon introduced a new lens with AF mount, so the internal motor in upper level bodies is a backward compatibility feature to support an older lens design. In production, Nikon has already replaced several AF lenses by newer AF-S designs. As more lenses will be updated, there will be less people interested in carrying and paying for AF bodies. Eventually, like metering with AI-S lenses today, AF motor will be a niche feature of top bodies. If Nikon ever launches its long-waited SLD body, it most likely won't contain an AF motor - these bodies have to be small and light.

Even if you are not likely to move to a body without internal motor soon, some of your family members or good friends (who you'd like to share lenses with) might.

As for speed, it will matter more in lens with lots of glass where a motor with more appropriate strength can be used. First lens motors (AF-I) were introduced in 1992 to provide faster focusing with 300/2.8 and 600/4.

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