The 105mm f/2.8 EX DG Macro sits in the middle of Sigma's range of 1:1 true macro lenses. Keenly priced, it is designed for use with full frame digital SLR cameras, but can also be fitted to DSLRs with smaller APS-C size sensors. It covers a similar field of view to a 158mm lens in 35mm format when fitted to Nikon, Pentax and Sony cameras with 1.5x crop factors or 168mm with Canon DSLRs.
Interestingly, Sigma produces a version of this lens for Four Thirds System (and Micro Four Thirds) cameras, where it covers a field of view equivalent to 210 mm. This and the 180mm f/3.5 APO EX DG HSM Macro are the only true macro lenses Sigma adapts for the smaller sensor format.
The 105mm f/2.8 macro shares many features with the 50mm f/2.8 EX DG we reviewed recently. It has the same EX (‘Excellence') matte finish on the lens barrel and supplied cylindrical hood and comes with the same DG (‘digital') coatings that minimise the effects of internal reflections off the surface of the sensor.
The Sigma 105mm f/2.8 EX DG Macro lens, shown without its cylindrical lens hood. (Source: Sigma.)
The optical design comprises 11 elements in 10 groups and includes three SLD (Special Low Dispersion) glass elements that correct colour shifts and ensure sharpness across the zoom range. A Super Multi-layer coating minimises flare and ghosting.
A floating internal focus system allows photographers to use a minimum shooting distance of 313 mm for a 1:1 reproduction ratio. This provides a working distance of 122 mm without the lens hood fitted - or approximately 90 mm with the lens hood in place. That's fine for taking close-ups of insects and small animals - provided they're not too flighty. The front element doesn't rotate, allowing angle-critical attachments to be used.
Like other lenses in Sigma's EX line-up, this lens looks very smart and feels solidly built. Weighing only 450 grams, it is 95 mm long at infinity focus, which is small enough to fit easily into a camera bag and compact enough not to be intimidating for portrait subjects.
The lens barrel extends by about 59 mm at the 1:1 reproduction ratio point. When the lens hood is fitted, this almost doubles the overall length of the lens - and it's a factor that must be taken into account when using the lens for macro work, particularly when the camera is tripod-mounted.
The inner barrel carries prominent reproduction ratio markings in white and yellow. The white markings apply when the lens is used in AF mode, while the yellow markings are for manual focusing. Six magnification ratios are provided for each, ranging from 1:1 when the lens is fully extended to 1:4 when it's pulled right in.
A 45 mm wide focusing ring sits just behind the front of the lens. It carries a 29 mm wide ridged rubber band that provides a secure grip. Sigma has employed a novel Dual Focus (DF) mechanism for switching between auto and manual focus. The focus ring is pushed forward to the AF position or pulled backward for manual focusing.
The manual position engages a clutch mechanism that links the lens to the camera's AF screw drive. Autofocusing can't be performed with Nikon's D40, D40x, D60, D3000 and D5000 cameras, which lack internal focus drive motors.
In manual mode, the focusing ring can be rotated through about 200 degrees (a little more than half a turn) and this extends or retracts the inner barrel. The ring can be turned in the AF position but it has no effect on the length of the inner barrel. (Manual over-ride of autofocusing is not supported.)
Behind the focusing ring is a distance scale, which is recessed into the outer barrel beneath a transparent panel. It carries distances in metres and feet from infinity to the closest focus of 0.313 metres. Just aft of the distance scale and a little to its left is AF limiter slider with two positions: Limit and Full. The Limit position restricts the normal focusing range to between 313 mm and about 385 mm (1:1 to 1:2 reproduction ratios) to minimise hunting with close subjects.
The front element is recessed about 20 mm into the lens barrel, protecting it from dust, scratches and sticky fingers - but also making it quite difficult to clean if required. The relatively small 58mm filter threading is located just inside the front of the inner barrel.
Sigma provides a cylindrical lens hood, which screws into this threading. It's tricky to attach and you can't fit the lens cap when the hood is in place, one of the few gripes we have with this lens. Nor does the hood reverse neatly over the end of the lens for storage (as the hood for the Tamron 90mm macro lens we reviewed recently does).
Because the front element doesn't rotate, you can attach a 77mm filter, such as a circular polariser, to the threaded end of the lens hood. Aside from the hood, only front and end caps were provided for our review, although we believe padded zip pouch with belt loop comes with this lens.
Handling
We conducted our Imatest tests of this lens on the EOS 5D, the standard body we use for testing all lenses of this type. However, we also fitted the lens to an EOS 40D body for some of our test shots. The metal mounting plate attached to both bodies positively and securely and the lens felt nicely balanced and comfortable to use on each camera. It would be equally at home on a lighter DSLR body - or a heavier professional camera.
Not unexpectedly, the greater working distances made this lens more comfortable to use than the 50mm macro we reviewed recently. However, it was still necessary to take care when photographing subjects at a 1:1 reproduction ratio and the working distance was a bit too short to capture highly mobile subjects (such as bees). The risk of shading subjects was significantly lower than we found with the 50mm macro lens and, although the hood could block off some of the light from the built-in flash, the flash was usable when the hood wasn't in place.
Swapping between manual and autofocusing was comparatively easy with the pull/push clutch mechanism. The autofocusing system was quite noisy and noticeably slower than we found with the 50mm macro lens. The focus limiter helped to reduce hunting at close distances but hunting was very common with high reproduction ratios.
When shooting hand-held, roughly 80% of shots were unsharp with the 1:1 setting, even when we used the centre AF point. This was caused either by slight hand-shake or subject movement. The very shallow depth-of-field, even with the lens stopped down to f/9, made precise focusing critical and exacerbated this situation.
The percentage of unsharp images diminished progressively as the magnification ratio was reduced to the point where almost all shots were sharp with the 1:4 setting. At this point, camera shake is the main contributor to unsharpness. Although we wouldn't recommend it because of diffraction softening, owners of Canon, Sigma and Sony DSLRs can stop this lens all the way down to f/45, while Nikon and Pentax users have a minimum aperture of f/32 and Four Thirds System users can go to f/22.
When used for portraiture, the review lens provided an excellent perspective, particularly with the EOS 40D body. Test shots were remarkably sharp and the slightly elevated contrast made every detail in the subject clearly visible. (This may not appeal to some subjects.)
Performance
Although it didn't quite reach the resolution of the Sigma 50mm macro lens we reviewed recently, the105mm f/2.8 EX DG Macro produced sharp and plucky images and turned in some very good results in our Imatest tests. JPEG files taken with the Canon EOS 5D were up to expectations for the camera's sensor with the peak resolution at f/9 and very high resolution between f/5 and f/16, where diffraction began to affect image sharpness.
Differences between centre and edge resolution were small throughout the aperture range, indicating excellent flatness of field - as you would expect from a high-quality macro lens. The graph below shows the results of our tests.
Lateral chromatic aberration was the lowest of the four macro lenses we reviewed in late July and early August 2010 and negligible at all aperture settings. In the graph below showing the results of our tests, the red line marks the boundary between ‘negligible' and ‘low' CA.
As expected from a fixed-focal-length macro lens, distortion was negligible. We found slightly greater vignetting at the widest apertures than with the 50mm lens. However, it was gone by f/4, another expected characteristic.
It was difficult to force the lens to flare by pointing it directly towards a bright light source. Normal backlighting produced some attractive results.
Bokeh was reasonably smooth, albeit with some slight outlining of high-contrast edges with the aperture stopped down. This was less noticeable at wide aperture settings.
Buy this lens if:
- You want an affordable macro lens that can also be used for portraiture.
- You'd like to photograph live insects and other small, not-very-mobile animals.
- You require edge-to-edge sharpness for copying.
- You want a lens that requires no readjustment when you fit filters.
Don't buy this lens if:
- You want fast and quiet autofocusing.
- You require built-in image stabilisation.
- You're not prepared to use a tripod for critical macro work.
IMATEST GRAPHS
Based on JPEG files taken with the Canon EOS 5D:
SAMPLE IMAGES
Taken with the Canon EOS 5D unless otherwise specified:
Vignetting at f/2.8.
Vignetting at f/4.
Camera tripod-mounted; ISO 200, 1/10 second at f/2.8.
Camera tripod-mounted; ISO 200, 1/332 second at f/2.8.
Camera tripod-mounted; ISO 200, 1/160 second at f/3.5.
Camera tripod-mounted; ISO 400, 1/125 second at f/6.4.
Camera tripod-mounted; ISO 800, 1/83 second at f/6.4. 1:1 reproduction ratio.
Taken with EOS 40D tripod-mounted; ISO 800, 1/49 second at f/9. 1:1 reproduction ratio.
Camera hand-held with weak backlighting; ISO 800, 1/790 second at f/2.8. 1:1.2 reproduction ratio.
Camera hand-held with strong backlighting; ISO 800, 1/790 second at f/2.8. 1:1.2 reproduction ratio.
Camera hand-held; ISO 800, 1/166 second at f/6.4. 1:1 reproduction ratio.
Camera hand-held; ISO 400, 1/332 second at f/6.4. 1:1 reproduction ratio.
Camera hand-held; ISO 400, 1/125 second at f/7. 1:2 reproduction ratio.
Camera hand-held; ISO 400, 1/500 second at f/2.8. 1:2 reproduction ratio.
Taken with EOS 40D tripod-mounted; ISO 200, 1/40 second at f/8. 1:1 reproduction ratio.
Taken with EOS 40D tripod-mounted; ISO 800, 1/25 second at f/8. 1:1 reproduction ratio.
Portrait taken with EOS 40D; ISO 400, 1/100 second at f/4.