What is It?
The Nikkor 18-140mm f/3.5-5.6G AF-S ED DX VR (phew!) lens appears to be sort of a double duty lens. First, it's filling in for the old discontinued 18-135mm, which was a very sharp but flawed lens that didn't have VR. Second, the new lens appears to be trying to up the ability ante for the 24mp sensor cameras, where even the well-behaved 18-105mm is showing its age. Nikon has gotten better with each generation of its convenience zoom designs (both DX and FX), and the 18-140mm is just another example of that.
At about 4" (100mm) collapsed and 17.3 ounces (490g), the 18-140mm isn't a small, light lens. That makes it about a half inch longer and 2.5 ounces heavier than the 18-105mm, which itself isn't exactly a small, light lens. By comparison, Nikon's latest 18-55mm is 2.5" long and 6.9 ounces (195g). The extra glass needed to extend the telephoto range of these zooms lenses generates a size and cost penalty you need to be aware of.
Still, having one lens that covers the 28-210mm equivalent range is indeed a convenience.
The 18-140mm has a very wide zoom ring at the front of the lens (over half the lens's length), and that ring covers the full focal length range in a bit less than a quarter turn. At 140mm, the lens extends another 2" (53mm) via two embedded barrel sections. These sections have less play and slop in them than many of the Nikon variable aperture zooms that use such designs. The 67mm front element does not rotate during zoom or focus. The front element is very close to the front of the lens, though, so be careful you don't zoom into something (or use the optional HB-32 bayonet lens hood).
The focus ring is a narrow ring near the rear of the lens and covers the full focus range in somewhat less than a half turn. No depth of field scale is supplied.
The lens has two switches, one for turning VR on or off (no Active mode position), and one to control autofocus versus manual focus. Only A and M positions are on the later switch. Both are on the left side of the lens when viewed from the shooter's position behind the camera.
The lens has internal focusing (no size or position change during focus) and one aspherical and one ED element. Close focus is about 18" (0.45m), but at 140mm that gives a respectable 1:4.2 magnification ratio (a 24mm wide object will record across about a quarter of the frame).
On FX bodies, the image circle is visible using the FX crop at all focal lengths. At 18mm and 140mm you can clearly see the left and right sides of the image circle in the FX frame, not just dark corners. This lens is not usable on FX cameras except when you set DX crop on them. Such tight image circles have implications on vignetting characteristics, which I'll get to in the performance section.
The lens sells for US$600 and is made in Thailand. Only caps are supplied with the lens; no other extra accessories come with it.
How's it Handle?
Not a lot to write about. While it's a reasonable large and heavy lens, it still balances quite well on my D5300 body; it doesn't make the combination front heavy or unbalanced, which the 18-300mm most certainly does.
The zoom ring on my sample is smooth but a bit stiff (that's generally a good attribute to have for zooms, otherwise they creep on you when you're not looking). The focus ring, however, seems loose and somewhat decoupled when in M mode. I would have liked more tactile feedback on the focus ring.
For a mostly polycarbonate bodied lens, the build quality is decent, and as I noted above, the front extension does not have the usual wobble I see in a lot of lenses with this extending design.
How's it Perform?
Focus: Focus is fast and quiet. I was a bit surprised by this, as most Nikkors with only an A/M switch use a slower, less capable focus motor. Continuous focus performance was good for a zoom with this much focal length range. I was pleased with the focus performance on all the bodies I tried it on.
Optics: Nikon's MTF chart held out a bit of hope for this lens. At the telephoto end, for example, the sagittal numbers look good, and even the meridional numbers weren't bad, with only a bit of field curvature to look out for. The wide angle end looked a bit worse overall in the MTF charts, with more suggestion that the corners would be softer.
In practice, I was surprised to find that at 18mm the lens seems sharper than at 140mm, which is not what the charts suggested. Center sharpness is excellent at 18mm on the D7100, and very good to excellent at 140mm. Corner sharpness in both cases is just what I'd call good. Not surprisingly, the telephoto end is as good as it gets wide open (smaller apertures generate diffraction impacts that come into play on the 24mp sensors). On the wide angle end, stopping down one stop gets you the best results the lens is capable of. Basically stay between f/4.5 and f/5.6 if you want the most acuity this lens can provide on the 24mp cameras. On the lower megapixel count cameras, I'd still generally say the same thing, though I'd modify the range you should stick to as f/4.5 to f/6.3 or maybe f/8.
For a Nikon design, one strange thing is that the falloff in sharpness from center to corner seems to be pretty much following the same curve throughout the focal range. The corners never get into the excellent range for me at any focal length or aperture combination. For the users this lens is destined for, that's probably fine, but don't think you're going to pull in really sharp corners on your 24mp camera without an AA filter.
Chromatic aberration is decently controlled, and really only shows up into clear visibility at the extremes (as in focal length and corners of the frame). All recent Nikon DSLRs correct for CA in camera for JPEG images, but they're probably not having to do a lot of correction.
Like CA, vignetting is corrected in camera for JPEGs by most recent bodies that you'd be using this lens on, and for JPEGs you can just ignore vignetting completely therefore. For raw files that you aren't going to correct with software, you'll need to stop down a full stop in order to reduce vignetting to reasonable invisible amounts, but I wouldn't characterize the vignetting as bad for the lens specifications. Indeed, there's a fairly wide area with lower levels of vignetting, and it's really tight in the corners that the light falls way down (one and two-thirds of a stop at 18mm, one and a half at 140mm). In the middle focal range there's not a lot of vignetting to start with. It's only at 18mm and 140mm that I can measure more than a stop of darkening in the corners. The problem is clearly image circle related: this lens has a very DX-sized image circle.
Linear distortion is a problem. The lens has a strong case of barrel distortion at 18mm (almost 3% average) and beyond 24mm we're already hitting pincushion distortion. which peaks between 50-70mm (about 3%), but is still highly visible at 140mm (about 2.5%). With this much linear distortion, correcting it in software will almost certainly reduce overall resolution towards the edges, unfortunately, as you're moving a lot of pixel data around. Coupled with edge sharpness that is already down a notch from the center, this poses a bit of a problem in getting lots of clean detail in corners, obviously.
Final Words
I'm not afraid to show my bias. Nikon has made a lot of 18-xx lenses for DX. 55 (3 times), 70, 105, 135, 140, 200, and 300 are your choices for xx. Back when we were using 6mp and even 12mp cameras, the compromises these convenience lenses made were not just tolerable, but sometimes nearly invisible. With 24mp cameras without AA filters, that's no longer true. Nikon is making 18-xx lenses that are truly consumer lenses.
Many amongst the 18-140mm's purchasers aren't going to really see a lot of problems with the lens. It's respectably sharp in the center, doesn't get bad at the edges, and the in-camera JPEG corrections will eradicate the CA, vignetting, and linear distortion. That type of user should be quite happy with the 18-140mm. The stuff in the center of the lens has good acuity, and you have that 28-210mm equivalent focal range people were all gaga over back in the 90's with their film SLRs.
To me, however, even the small step beyond 16mp sensors means we need (and deserve) better optics now. I was hoping that the 18-140mm would have delivered what we really want to see at 24mp. It does in the center, but not at the edges, especially once you correct the linear distortion So, in essence, it still has to be regarded as a convenience lens. If you need the convenience of its focal range, then by all means snap it up: it's a bit better in most respects than the 18-105mm, which was one of my previous convenience zooms of choice (the other being the 16-85mm). Nikon has made this a no brainer for some: the 18-140mm was offered as a "kit" lens with some recent DSLR body closeouts at far less than its implied US$600 cost. There were some D7000 and D5200 kits offered with the 18-140mm that were actually really good bargains, all things considered.
But if you're buying it at the US$600 retail price, you have to think a little harder. That's three-quarters the price of the Sigma 18-35mm. Here's the thing: when you compare the Nikkor 18-140mm to the Sigma in the 18-35mm range, the Sigma smokes the Nikon. True, the Sigma is a bigger, heavier lens, and it doesn't have much of a focal length range. But when you compare the results in the overlapping range, you just can't get excited about the 18-140mm. Likewise, the Nikkor 35mm f/1.8 outdoes the 18-140mm at 35mm. So if you're buying a 24mp DSLR—which I should note that all of Nikon's current DX DSLRs now are—you can have really great lens performance or a convenient focal length range. I'm not sure why you're buying a 24mp camera if you're opting for the latter, though. Which is where my bias comes into play (quality over convenience).
This makes the 18-140mm difficult to recommend. It doesn't have any glaring fault (other than too much linear distortion for you straight line folks). It's actually a pretty nice lens, and a step up from the 18-105mm in a number of ways. But it doesn't make 24mp DSLRs sing. The snap just isn't fully there that would allow me to give it an unequivocal recommendation.
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