A New Standard

If you are a regular reader of this blog then you’ll be aware that I’m trying to transition from my full frame Canon DSLR to a full frame Sony mirrorless system without spending a fortune. Initially the idea was to buy a second hand A7r ii body and use second hand lens adapters (the Sigma MC-11 and the Metabones V Smart Adapter) to enable me to use my existing Canon EF lenses. The experience went relatively well until I tried to use the kit for covering a couple of events. It was my experience of using the Canon 24-70mm f4 IS L lens mounted via the Metabones V Smart Adapter that made me start to reconsider the whole idea of adapting Canon EF lenses to Sony FE bodies. I’d already been using a Sony 28-70mm f3.5-5.6 OSS lens and while the AF and the stabilisation were good points I wanted a brighter lens and a constant aperture as it makes life easier when doing flash photography. My options in this focal range were:

Sony Zeiss FE 24-70mm f/4 ZA OSS Lens
Sony FE 24-70mm f/2.8 G Master Lens
Tamron 28-75mm F/2.8 Di III VXD G2 Lens
Sigma 28-70mm f2.8 DG DN Lens

The Sony Zeiss 24-70 f4 doesn’t have a very good reputation as there is a lot sample variation and it would appear that good copies are few and far between. Sony’s f2.8 GM, well at just under $3000 AUD was out of the running on price alone. With the Tamron 28-75mm well the original version is permanently out of stock here in Australia so goodness knows when the mk ii version will be available. So the Sigma won the day.

Sigma 28-70mm f2.8 DG DN Lens available in both Sony FE mount and L mount.

TLDR

Specifications

Focal length	28-70mm
Angle of view	75.4~34.3°
Maximum aperture	f2.8
Minimum aperture	f22
Filter Size	67mm
Stabilisation	no
Maximun magnification	At 28mm 1: 3.3 At 70mm 1: 4.6
Minimum focusing distance	Ay 28mm 19cm At 70mm 38cm
Focusing modes	AF and manual
Optical construction	12 groups, 16 elements Including 2 FLD elements, 2 SLD elements, and 3 aspherical elements
Aperture blades	9 rounded blades
Weather sealing	dust and splash-proof
Weight	470g
Dimensions	φ72.2mm × 103.5mm
Mount	Sony FE and L-mount Alliance

Build Quality

The 28-70mm DG DN is part of Sigma’s “Contemporary” line which up to recently was seen to be their line which had good optical performance while cutting costs in the materials and finish. Recent releases such as the 90mm f2.8 have muddied this somewhat as they spare no expense seemingly in their construction and performance. Anyway back to the 28-70 it has a more utilitarian approach to its design – it has a rather plain matte black appearance and is made out of Sigma’s Thermally Stable Composite which is a kind of engineering grade plastic that has similar thermal expansion properties as aluminium. The lens is compact and relatively light when compared to other standard zooms with a f2.8 constant aperture. When you pick it up it doesn’t feel cheap or flimsy, but rather it feels reassuringly dense and solid. Nothing creaks or flexes and there are no mould seams – Tamron I’m looking at you! The lens mount is chrome plated brass and there is an ‘o’ ring to prevent the ingress of moisture and dust.

The chrome plated brass mount and the “o” ring that surrounds it.

Compared to other lenses there is a paucity of controls – just a focus ring, a zoom ring and a focus mode selector switch. Both rings have a nice ribbed rubber texture to facilitate a good grip. The zoom ring has a smooth 90º which has just the right amount of resistance – not too sloppy or too tight. The lens barrel extends as you zoom to 70mm by 27mm. The focus ring is of the fly by wire variety with no hard stops. Again it is not too loose or tight and I found it quite pleasant to use.

The controls on the lens are few and far between. A focus ring, an AF mode switch and the zoom ring.

The lens comes with a plastic lens hood that bayonets into place securely. A nice touch is that the interior is ribbed to prevent reflections. The filter size is 67mm which is a modest size and keeps the cost of filters down. The first standard zoom I got had a filter thread of 55mm. Subsequent standard lenses went increased to 77mm and then 82mm so it’s good to see sizes slipping back.

The lens barrel extends by 27mm when zoomed out to 70mm. The lens comes with a petal shaped lens hood.

In terms of size and weight, well my Sigma 16mm f1.4 and Olympus 45mm f1.2 are almost as big and as heavy as the 28-70 DG DN and they were made for the micro four thirds system. It’s a little larger than the the Sony 28-70mm f3.5-5.6 OSS lens and while the same length as the Canon 24-70mm f4 IS L the Sigma is 135g lighter.

The Sigma 28-70mm f2.8 DG DN lens is only fractionally bigger and heavier than the Sigma 16mm f1.4 and Olympus 45mm f1.2 prime lenses for the micro four thirds system.

Optical Performance

To see any of the images larger just click on them.

OK lets get down to the nitty gritty. At 28mm wide open the centre of the image is sharp and contrasty. The edges are softer and there is a very, and I mean very, small amount of green fringing. Switching off the lens correction we can see that there is vignetting and barrel distortion. At f8 the edges catch up with the centre sharpness. By f16 the effects of diffraction are noticeable.

At 70mm f2.8 the centre performance is not as good as the wide end being slightly soft and lacking contrast in the centre and with corners a little worse. Stop down to f4 and the centre improves considerably and by f8 the corners are as good as the centre. Again by f16 diffraction is apparent. Without the lens profile there is vignetting and pincushion distortion.

When it comes to chromatic aberration well axial (or longitudinal) CA can be observed when shooting wide open especially at the minimum focusing distance. This is easily dealt with by stopping down. It is more pronounced at 70mm than 28mm. Transverse (lateral) CA is very well controlled and images need to be forensically examined at 200% to spot it. Very impressive.

Ghosting flare, sensor flare and diffraction spikes. 28mm at f22. I you look carefully you can see a small amount of ghosting flare and some sensor flare.

Looking at the diffraction spikes (sun stars) for this lens the nine bladed diaphragm produces 18 points and stopping down to f22 produces the best effect. Diffraction blurs them a little but I quite like them.

Flare resistance is very good. There is little to no veiling flare and just a little ghosting flare. What is apparent is sensor flare aka red dot flare. This is caused by reflections from the micro lenses on the sensor hitting the rear lens element and the being reflected back onto the sensor. Unfortunately it seems that mirrorless cameras seem more prone to this due to the shorter lens flange distance.

Looking at the bokeh at 28mm wide open at f2.8 the balls don’t have a round shape – they are a bit misshapen and have visible onion rings. The tonal transitions are smooth. By f8 the balls take on a polygonal shape. At 70mm wide open the balls in the centre of the frame are nice and round with some onion rings. At the edge of the frame they have an elliptical cats eye shape. The tonal transitions in out of focus areas are again nice and smooth. Stopping down to f4 the balls become tighter and the onion rings not so prominent. Interestingly the bokeh balls keep their round shape all the way down to f22.

Auto Focus Performance

Shooting stills wide open at 28mm the autofocus is very snappy and sticky in daylight with lots of contrast. I shot several sequences of me walking towards the camera and achieved a 100% hit rate. At 70mm f2.8 the results weren’t as impressive but I averaged out with a hit rate of 81%. The problem seemed to occur when I got very close to the camera and the lens would struggle to keep up. It would focus for a couple of frames, loose focus for a frame and then re-acquire. Using the 28-70 DG DN with my Sony A7 r ii at a grip and grin I found that the AF wasn’t as confident in the low light and contrast setting. It wasn’t terrible but I found it wasn’t as quick as I’d of liked and a couple of times I lost a spontaneous moment because the combination hadn’t acquired focus quick enough.

When shooting the video test I mounted the camera on my slider with a repeating 20cm movement and then filmed myself walking back and forth. At 28mm wide open the lens did very well with just a couple of moments where it was hesitant. Overall a very good performance. At 70mm the AF wasn’t as confident and prone to loose focus and then not quickly re-acquire. I decided to re-test but not using the slider this time and everything was a lot better at both focal lengths so from that I can assume that the movement from the slider was stressing the autofocus too much.

Checking for focus breathing I found that it was very minimal which should keep the video crowd. Normally I don’t bother checking where a lens is parfocal or not, but, as the lens had so far done so well I thought I’d give it a go. And the Sigma 28-70 f2.8 is indeed parfocal.

Conclusion

Sigma 28-70mm f2.8 DG DN Lens mounted on a Sony A7r ii.

There have been a few criticisms about the Sigma 28-70 DG DN. People moan about the distortion present when you don’t use the lens profile. I would argue that using corrections like that enables manufacturers to make compact, lightweight and affordable lenses. Other have been very vocal about the reduced performance at the 70mm end, but it is not unusual for a zoom lens to be better optically at the wide end. Better performance would again mean bigger, heavier and more expensive lenses. The main criticism is that at 28mm it’s just not wide enough and that it really should be a 24-70mm f2.8. Well Sigma does make one and its $600 AUD more expensive and it is bigger. Sony’s GM 24-70mm f2.8 is $1300 AUD more expensive, 371g heavier, 33mm longer and 14mm wider. So if you want a small compact f2.8 constant aperture standard zoom some compromise has to be made and I think Sigma has made the right choices.

The focusing and zoom rings have a nice ribbed rubber grip.

I really like standard zooms – I have one for each of my camera systems (Canon EF, M4/3, and now Sony FE). I find they fit in with my way of working with just one camera and one lens. This lens with its useful close focus ability makes it ideal for shooting small subjects, food, and products. Its constant f2.8 aperture is good for low light, flash photography and video. While 70mm at the long end makes it a bit on the short side for some types of portrait photography the focal range is great for environmental portraiture. Overall this lens is perfectly suited to being used as an everyday carry or part of a lightweight travel kit. Occasionally I wished for something a little wider, so what I ended up doing was carrying my Tamron 20mm f2.8 and then everything was just dandy.

I really enjoyed using this lens. While it’s not perfect by any means it is a very solid and workman like performer that lets you get on and take photos.