No.6 x 2.75 (3.5mm x 70mm) TX Countersunk Self-Tapping Screw - Stainless Steel (A2) (Pack of 20)

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So if I have to augment the 28-70 with two additional lenses, I might as well save weight/space and gain capability with a single prime. Sharpness drops off a little at the corners on the wide end at F2.8, but stopping down to F5.6 gives a relatively flat field of focus and improved corner sharpness. That said, focusing in the corner yields higher corner sharpness than focusing in the center and stopping down, indicating a curved field of focus. Focusing in the corner and stopping down yields even better corner sharpness, as expected. The not-so-flat field of focus, at least in part, contributes to the peripheral softness when focusing centrally. This lens is a joy to use. It just works, never gets in the way, and yields great results. Just be careful not to let the sun shine into it for fear of veiling flare. The Nikon 35-70mm f/3.5 AI zooms by moving the elements inside the barrel. Nothing moves externally except the zoom ring. Roll your mouse over to see what happens. I moved the focus a little between shots; pay attention not to the focus ring but to the glass which is moving up and down. This 35-70mm f/3.5 AI was Nikon's first professional midrange zoom from 1977. It is very sharp at every setting and has a constant f/3.5 aperture. It has less distortion than any of Nikon's f/2.8 zooms, and that means much better than the 24-70mm AF-S and 28-70mm AF-S, each of which costs over ten times as much.

Stopping down to F5.6, we see a slight improvement in sharpness at wide-angle and a bigger improvement at telephoto, since the lens is softer wide open at 70mm than it is at 28mm. You'll appreciate this improvement in sharpness more if you're shooting with a high-resolution camera. We tested with both the 42-megapixel Sony A7R III and 47-megapixel Panasonic S1R; with a 24-megapixel body, that difference would be much less noticeable. So when does a zoom make sense? When it covers more than one easily discernable FL. But 28-70 doesn't do that. It has a single useful perspective for me. A "normal" perspective. I would need to augment it on both sides with a lens that is wider and a lens that is more tele. And since it is so lightweight, balance is very good. Regardless of the mount variant you choose, it shouldn't feel front-heavy on any body you might want to pair it with. Vignetting is not a concern for the Sigma 28-70mm F2.8. It's only really noticeable at telephoto, and even there is minor and easily corrected. Bokeh NIkon made a 43-86mm f/3.5 zoom before this, but since it is neither a normal zoom (43-86mm is normal to tele), and since it was never pitched as a professional zoom, I'm not counting it as Nikon's first pro normal zoom. The 43-86mm was a convenience zoom, not a zoom with which to earn one's living.Results at 70mm follow a similar pattern, but with softer results overall, particularly at close focus distances. Wide open, portraits can often look a little dreamy. In terms of video autofocus, the Sigma 28-70mm DG DN has the potential to be a really great option. Not only does it offer silent autofocus drive and very nicely-damped manual focus, but it also has well controlled focus breathing. There's only a bit at the 28mm wide-angle end and very little at all by the time you zoom in to 70mm.

Compatibility: On the D2, D3, D200, D300 and F6, use the "Non-CPU Lens Data" menu option to input the zoom setting and f/3.5, which will give you full matrix metering and EXIF data, and finder read-out of set aperture. It works great in aperture-preferred as well as manual modes on these cameras. Production History: The 35-70mm f/3.5 AI was introduced in 1977 and built until it was replaced by the 35-70mm f/3.5 AI-s in 1981. Nikon made about 50,000 of these AI versions. A little bit of longitudinal chromatic aberration can be seen as magenta and cyan color fringing around high contrast edges in the image above. It's subtle enough to be a non-issue for the most part, and goes away as you stop down the lens. Sunstars are relatively pleasing, with 18 rays thanks to the nine aperture blades. They're not as tight as they could be – each ray splits and diverges into two rays – and as expected stars on the wide end look better than those on the telephoto end where they can appear a bit 'messy'.Shooting wide-open at F2.8 (which you'll quite likely want to spend much of your time doing if you've bought this lens for its bright maximum aperture), sharpness is very acceptable in the center of the frame at 28mm and remains pretty good even once you zoom in to the 70mm telephoto.