The 24-85 on FX is slightly wider range than the 18-55 on DX (which is equivalent to about 28-80), and it's slightly faster (f/3.5-4.5 vs f/3.5-5.6). You'll also notice that it focuses a bit more quickly, doesn't make as much noise whilst focusing - and is quite a bit bigger and more expensive. It is a nice lens.
_____ Brian... a bicoastal Nikonian and Team Member
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Sat 25-May-13 09:03 PM | edited Sat 25-May-13 09:05 PM by jamesvoortman
A really nice general purpose zoom lens for the D5100 was the 16-85. The equivalent to this on FX is the 24-120 f4 which is a great lens.
the FX "equivalent" of your 18-55 DX lens is the 24-85 that is often sold as a kit lens for the D600. Testing has shown this lens hardly gives anything away to the more expensive options in terms of image quality, it is just slightly slower, lighter and less expensive.
if budget is not your concern, would you consider 24-120 f/4. The image quality is better.
Although there is an overlapping in the 70-120 range, you do not need to change the lens so frequently when you want to take picture at this range. You may have the same experience that if your subject is just a bit too small to fill the frame, you may just take the photo and then crop it later in the post processing. With the extra focal length in 70-120mm, you get more pixels after final cropping.