Sigma tend to do what Canon do; provide a range of similar lenses but with varying features. As an example, I have the 150-600mm Sport lens, which is fantastic; it's weather-sealed, has great autofocus, and full image stabilisation, but it's still ~£1300, which is a lot of money. It also weighs quite a lot. However the image quality is exceptional and by no means worse than anything else on the market in that range; it punches at the same level as the Canon 100-400mm IS II, which is about £800 more.
So they also do a 150-600mm Contemporary model, which has 90% of the performance. It doesn't have full weather-sealing, and it has a different element arrangement which slightly changes the picture quality, but it also drops a huge chunk off the weight and about £400 off the price. It's not quite as solidly built but for a lot of people it's more than enough and provides a good alternative.
In my personal experience Sigma lenses tend to be heavier than Canon for equivalent build quality. ~10 years ago I'd say the picture quality was slightly poorer, but now they compete very well in a variety of ranges.
So they also do a 150-600mm Contemporary model, which has 90% of the performance. It doesn't have full weather-sealing, and it has a different element arrangement which slightly changes the picture quality, but it also drops a huge chunk off the weight and about £400 off the price. It's not quite as solidly built but for a lot of people it's more than enough and provides a good alternative.
In my personal experience Sigma lenses tend to be heavier than Canon for equivalent build quality. ~10 years ago I'd say the picture quality was slightly poorer, but now they compete very well in a variety of ranges.