The Sigma APO 150-500mm F5-6.3 DG OS HSM (otherwise known as the BigmOS) is an ultra-telephoto lens designed primarily to replace the range covered by their discontinued APO 170-500mm F5-6.3 DG model. It represents a fairly low-cost alternative to the high prices commanded by OEM lenses that cover the extreme end of the telephoto range.
The lens, in comparison to OEM lenses, carries only a fraction of the out-of-pocket cost of the most popular high-end glass. It also has a little bit more reach than most of that crop of lenses offer, as typically you see the top end of the zoom range at 400mm. Even the more competitively-priced Nikon glass will not afford the extra 100mm of range offered by the Sigma lens.
Build quality appears to be fairly robust. The lens has Sigma’s typical black matte finish, and comes with front and rear caps, a somewhat undersized lens hood, a removable tripod collar, and a large padded carrying case. The lens is big, and it’s heavy. Bringing it up to shooting position is definitely going to build some muscle, and carrying it around all day will be a chore. The weight will cause zoom creep as soon as the lens barrel is tilted downward, so there’s a lock switch that operates when the lens is set at its 150mm focal length.
The focus ring operates very smoothly, and the HSM motor allows high-speed AF and full-time manual adjustment, so it’s not necessary to move the switch from A to M to refine your focus point. On the other hand, the zoom ring is stiff and clunky at best. What’s more, the zoom ring turns backward. I am used to turning my wrist clockwise to zoom in — in this lens, you’d turn your wrist counter-clockwise to zoom in, and that takes some getting used to. The focus ring is closer to the focal plane than the zoom ring is, and I found that when turning the zoom ring, I would occasionally disturb the focus.
Image quality is quite acceptable, although sharpness is best, as one might expect, through the middle of the zoom range — between 200mm and 400mm. The lens also performs best somewhere between f/8 and f/11. This is definitely a daytime, bright-light lens. Colour and contrast reproduction are quite good. The lens hunts only in very low light, and focus speed is very fast.
The OS is definitely a benefit, and worked well enough for me to be able to hand-hold at 1/100 and f/6.3 with the lens racked out to 500mm. I was even able to shoot at 6 fps under those conditions with the OS engaged with good results. With OS disengaged, it becomes a chore to get sharp photos at a shutter speed lower than 1/500 of a second. You’ll definitely know when the OS is at work, because it’s loud.
Against a bright background, there will be some colour fringing observable at high-contrast edges of your subject, but those are very easily removed in post.
If you’re not a pro, and you’re looking for something with extended reach, you could do a lot worse than this lens. You won’t get the IQ from it as you will from Canon’s L glass or from Nikon’s high-end lenses, but then again, you’ll pay only $1 000 for this lens, and at that price, I’d consider it a bargain.