[eeyore]

Originally Posted by Fourwings

In my opinion forget the 170 - 500, its focusing is slow and very noisey, plus the quality of the glass is not as good as the EX range lenses.

I own the 50 - 500 (Bigma) and would happily recommend it to anyone, it consistantly produces quality images, is well built, very fast focussing & quiet and handles very well.

However, a friend of mine has just invested in the 150 -500, this has the added advantage of Sigma's Optical stabilisation system (OS), it has the same focussing system as the Bigma so it is reasonably quiet although you can hear the stabiliser start up. The biggest single advantage to this lens is that you can get good results handheld, whereas the Bigma requires a tripod or monopod for about 90% of the time.

i would agree that the 150 and bigma are better than the 170 - but i wouldnt forget the 170 if money is tight. i have used one for three years and find it pretty good - the focus is noisy definitely (which is why its AKA the coffee grinder) but it isnt particularly slow except in very low light. and the glass is a bit of a red herring, unless you are planning to useit on a full frame sensor, as the majority of the chromatic aberation occurs at the edge which a cropped sensor can't see anyway.