Somebody in another thread suggested that we start a lens sample thread for the Sigma 50-150mm f/2.8, and I couldn't agree more. Much like its big brother Sigma 100-300mm f4, this is an incredible lens that was tragically discontinued well before its time. It was relatively unknown when it was available, and does not seem to have been manufactured in large numbers. This makes it very hard to find on the used market, and those who own a copy tend to hold onto it. And just like the 100-300mm f4, the value of the 50-150mm seems to have increased since it was discontinued, with used copies fetching higher prices than when they were new.
The Sigma 50-150mm f/2.8 was the only direct competitor to the Pentax 50-135mm f/2.8. These lenses are designed to cover an APS-C sensor, and are meant to be approximately equivalent to using a 70-200mm lens on a full-frame/35mm camera. Both lenses are nearly the same size and weight. Which is to say, they are both much smaller and lighter than the 70-200mm f/2.8 lenses they are designed to emulate.
While the Pentax is a very nice lens and is weather sealed, the Sigma 50-150mm has several advantages. Many people who have had a chance to compare the two lenses have concluded that the Sigma is the sharper lens. The Sigma also has more reach. And what's more, the Sigma is arguably sharper at 150mm wide-open than the Pentax is at 135mm.
But the biggest advantage may lie in the autofocus motor. Both lenses have a silent autofocus motor and allow full-time manual focusing, but the Sigma's HSM is much faster than the SDM in the 50-135mm, making the Sigma a much better choice for keeping up with action. Sigma's HSM also seems to be very reliable in the long term, with very few reports of motor failure. Unfortunately, the same cannot be said of the SDM in the 50-135mm. Based on the number of first-hand accounts and informal poling on this site, failure rates for the 50-135mm are shockingly high.
Before getting to the samples, I'll post a few images with the lens mounted on my Pentax K-x. The K-x has since been replaced by a white K-30, so I may eventually get around to adding some pictures of the lens on my K-30.
Last edited by Edgar_in_Indy; 03-04-2013 at 05:45 PM.