It's a 4.5-6.3 lens, so not exactly fast. If you need high SS to freeze action, you may be setting yourself up for disappointment with a 500D, since you are in a part of the world not renowned for very good light! I used the lens in India last summer and it was phenomenal but the light there was, pardon the pun, a revelation, given that I am from Oregon which gives Blighty a run for its money in terms of gloomy weather. But back home here, it will struggle on very dark and cloudy days for birding, which is what I use it for. The alternative however, is a big white, like a 500/4 or 400/2.8, which is in a different league, cost wise.