The photo below shows the Sigma 70-200mm f2.8 lens. What is nice about this lens is that it is f2.8 throughout the zoom range rather than changing as you zoom. That lot weighs about 3kg so not something for hanging on your neck. Either use a tripod/monopod or a Blackrapid strap so it hangs across the shoulder and not your neck.
The other two lenses are the Sigma 70-300 zoom that was £99 and a 500mm Tamron mirror lens. The Tamron is lightweight and good for long distance and wildlife but you need to whack up the ISO for any hand-held use. You also get some nice/weird donut bokeh with it. Think it is about f9. On a film camera it is 500mm but on my DSLRs it has a x1.5 factor so works as a 750mm! Try hand holding that and getting sharp images!
The other two lenses are the Sigma 70-300 zoom that was £99 and a 500mm Tamron mirror lens. The Tamron is lightweight and good for long distance and wildlife but you need to whack up the ISO for any hand-held use. You also get some nice/weird donut bokeh with it. Think it is about f9. On a film camera it is 500mm but on my DSLRs it has a x1.5 factor so works as a 750mm! Try hand holding that and getting sharp images!