Richard Sibley compares APu2019s Fixed Focal Length Lens of the Year, the Sigma 105mm f/2.8 EX DG OS HSM Macro, with 90mm and 100mm optics from Tamron and Tokina, and explains why such focal lengths are so enduringly popular
Image: The images for the resolution chart were taken at each full aperture with both the Canon and Nikon versions of the Sigma lens. At f/8, the Canon-fit Tamron lens and Nikon-fit Tokina lens match the performance of the respective Sigma versions. All in all, there is little difference between the lenses, although the Tamron and Sigma models are slightly sharper than the Tokina optic.
When the fine details produced by all three lenses are closely examined, it is very difficult to single out one model as being vastly superior to the others. On this occasion, the Tamron 90mm lens has been tested on a 21-million-pixel Canon EOS-1Ds Mark III, while the Tokina 100mm lens has been tested on a 24-million-pixel Nikon D600. As a comparison, two Sigma 105mm lenses have been tested on both the Canon EOS-1Ds Mark III and the Nikon D600.
Referring purely to the resolution chart images, it looks as though the Sigma and Tamron lenses have an advantage over the Tokina optic. However, real-world examples show otherwise, with the Tokina capable of resolving just as much detail as either of the other lenses. The close-up of the eye in the portrait images is testament to this.
Naturally, all the lenses are at their sharpest at f/8, although the best range is f/5.6-11. There are a few issues when the lenses are used wide open, although at f/2.8 all three lenses display strong purple fringing on high-contrast edges. Stopping down to f/4 reduces this effect, with the Tamron optic looking the best of the three. At f/5.6, the Tamron lens is virtually free from purple fringing, while there is still a hint of it from the Tokina and Sigma lenses. By f/8, all three lenses are reaching their peak performance, as the fringing has gone and the lenses are at their sharpest.
Diffraction starts at around f/16. At this setting there isn’t much loss of detail, but images are slightly softer, which appears to be largely due to a reduction in contrast. There is a notable drop in quality at f/22, with a loss in contrast and the images becoming softer. However, despite a lack
of sharpness, it is still possible to discern a good deal of detail in our resolution chart test, which is, of course, important to macro photographers wishing to maximise depth of field.
One area where all three lenses are equally proficient is curvilinear distortion. None of the lenses displays significant barrel or pincushion distortion. Even when viewing an image of our distortion chart at 100% with a horizontal line across (to gauge any warp), only a very fractional shift of a pixel or two is noticeable.
Using Adobe Camera Raw’s automatic lens correction feature, which is based on calibrated lens profiles, there was little difference with the correction turned on or off, with the correction of vignetting being far more obvious.
There is quite a lot of vignetting apparent when each of these lenses is used wide open at f/2.8. I don’t find this too much of a concern if shooting digitally, as it is easily removed in software. I also like the fact that slightly darker edges can draw the eye to the centre of the frame, which, in the case of a macro or portrait image, is where the subject will most likely be.
At f/4 vignetting is softened, and by f/5.6 it should be virtually unnoticeable, unless photographing a wall or another flat uniform subject. At f/8, none of the lenses displays any vignetting, which is good news for anybody using the lenses for reproduction purposes. With virtually no curvilinear distortion or vignetting, and each lens being very sharp, all three are superb for reproduction of flat paperwork.
Images: Not only do these lenses work well for macro photography, but they are also perfectly suited to taking portraits. The 100mm focal length gives a largely distortion-free result and each lens is capable of very sharp results, as can be seen in the pull-up of the eye