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

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We didn't see any major issues with lateral chromatic aberration for this lens. There's a truly minute amount of it, perhaps 2-3 pixels wide on a 42MP image (that's a half a millimeter on a 40" x 60" print) that clears up easily if you enable CA corrections in-camera or in your Raw converter. On the telephoto end the maximum magnification ratio is 0.22x. Close-up subjects shot at 70mm can appear soft and dreamy.

Life is all about compromises. With a bright, continuous aperture and minimal size and weight being the key elements of its design, it's not surprising at all that the Sigma 28-70mm F2.8 DG DN's image quality can't quite compete with larger, more expensive alternatives like Sigma's own 24-70mm F2.8 DG DN Art. 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'. Proper fraction button and Improper fraction button work as pair. When you choose the one the other is switched off. As a two-ring zoom it's best for use on a tripod. Hand-held, I constantly need to grab zoom, then focus, then zoom, then focus, etc. I can't do both at once as I can with a one-touch zoom. It holds focus while zoomed. Of course if you focus at 35mm you don't have enough precision to ensure focus at 70mm. Focus at 70mm and the focus holds as you zoom wider.But if what you need most of all is portability and you understand the compromises necessary to achieve it, the Sigma 28-70mm F2.8 DG DN is hands-down the smallest and lightest of the bunch and still offers solid image quality. 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 The 35-70mm f/3.5 AI is a great lens for film and FX Digital. It's silly for DX digital because there are far more modern DX lenses that do a much more convenient job.

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. Proper fraction button is used to change a number of the form of 9/5 to the form of 1 4/5. A proper fraction is a fraction where the numerator (top number) is less than the denominator (bottom number).

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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.