[PieEater]

Hi,

I recently bought a 450d packaged with the 18-55 kit lens and the 55-250 IS lens.

I mostly photograph wildlife, birds and aircraft so the longer lens is usually the one attached to the camera, though at some point I would like to experiment with landscapes, still lifes & macro's (insects / animals / flowers).

The main problem I have with the 55-250 IS is that whilst it is capable of some great shots the auto-focus is fairly slow for tracking fast moving birds in flight (I regularly go to bird of prey displays) and even with fairly static subjects it's at most 80% reliable in the best of conditions. I would also appreciate some additional focal length as often with wildlife 250mm is not nearly enough. I haven't really made enough use of the 18-55 to form an opinion of it yet.

My budget is always going to be limited, but rather than regret buying a cheaper alternatives I'd rather wait until I could afford something I'd be happy with.

My first purchase will obviously need to replace the 55-250 and make up for it's shortcommings. I have read the recent PhotoPlus review and it seems like the Sigma 120-400 lens is a good price/performance bet over the Canon 100-400, however I don't know how much better the image quality and auto-focus would be over what I have. Also I'm lacking a fast lens so I was wandering though it would be a more expensive option whether the Sigma 70-200 2.8 and a Sigma 2x teleconverter would be a better bet in the long run, how would this combination compare with the 120-400 lens in terms of quality and focusing?

I'd also appreciate any suggestions as to another lens that I could look at that might let me combine Macro, landscape and still life, or is this too much to expect from a single lens?

Thanks in advance.