Sigma 18-125 mm f/3.8-5.6 DC OS HSM
- sturdy body for this class,
- very good image quality at the center of the frame at all focal lengths,
- good image quality at the edge of the frame in the range 18-70,
- the lowest distortion in this class,
- the lowest vignetting in comparison to the competition,
- sensibly corrected coma,
- quite good work against bright light,
- silent, fast and accurate autofocus,
- efficient image stabilization.
- worse image quality at the edge of the frame at the maximum focal length,
- large distortion at the wide angle.
At the beginning, some casual digressions. I am thinking about sense of introducing on the market a lens of this class and parameters. Sigma already has a good model of 17-70 mm parameters, which on account of good brightness, good optics and usable macro is often chosen by prosumers. For a change, beginning photographers’ mind will be more stimulated by mega-zooms, which are also found in Sigma’s offer (e.g. optically good 18-200 mm OS or the brand-new 18-250 mm OS). Who’ll be interested in a lens of medium parameters 18-125 mm? To be frank, I don’t know.
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Especially, as there’s one more problem. 18 mm focal length is the equivalent of analogue 27 mm for sensors o 1.5 factor. In case of Canon, and what’s more important Sigma itself, it’s not that bright. Sigma’s Foveon is characterized by 1.7 factor compared to the full frame, so 18 mm focal length corresponds to full-frame 31 mm. In the situation when Sony gives its owners “kit’s” substitutes beginning at 16 mm, Sigma with its 18 mm mounted on its own DSLRs gives a weak performance, because the difference in the field of view at the wide angle reaches almost 14 degrees. Being a photo-amateur having a Sigma or Canon DSLR I’d exchange 20-40 mm at the long end for 2-3 mm at the shortest focal lengths. I’d definitely be more interested in a model of 15-80 parameters, even with aperture f/3.8-5.6, then those 18-125 mm. I realize that such a lens is more difficult to manufacture and it has to cost more, but I think it would find more buyers than an appliance of 18-125 mm parameters.
It’s not our job to evaluate producer’s decision, though, and worry about the sale levels. Our job is the evaluation of optical and mechanical characteristics of the tested lens and let’s focus on that.
Sigma wanted to have their own part in the market of lenses of focal lengths starting at 16-18 mm and ending 105-135 mm. And to be honest, compared to the competitors it performs well. It’s decent optically, in some categories being slightly better than the competitors, in some slightly worse. As far as mechanics and solidity of used materials are concerned, it predominates over the Nikkors, but draws with Sony 16-105 mm being at the same level. For a change, the presence of ultrasonic motor is a chief asset over Sony, but not over the Nikkor which have their own SWM. The summary of all these characteristics shows Sigma in a favorable light. There is one serious reservation, though. Both Nikkors and Sony 16-105 mm are often sold in kit with a DSLR, so the buyer doesn't have to pay as much for them as for Sigma which when is buying separately costs around 340 $…
I’m reading what I wrote once again… Maybe I’m complaining too much? The comparison of pros and cons come out very well for this lens. And let’s stop here, because that’s the most objective approach.