Sigma 70-300 APO DG, sweet spot?

Bought this lens not long ago and haven't had time to really get familiar with it, impressed as anything with the quality considering it's strictly budget price. Were off to Kakadu National Park for holidays and will be taking a lot of widlife shots so the telephoto end will get quite a workout. Some of our 300mm shots have been really good but others less so, I seem to recall another post somewhere saying there were certain combinations of zoom and aperture that worked a lot better than others on this lens...any hints for getting the best out of it?

Hal55

I found with mind that stopped down to f/8 its pretty decent even at 300mm. up to 200mm in general for its price it is quite good, drops off a bit after that but you can still get some really nice photos.

you can see my photos taken with this lens here: http://ospi.smugmug.co​m/gallery/2430589#1274​37341

Most are over 200mm mark and the exif is intact if you want to see settings used.

I have a variety of shots here, many in the f/8 range but others stopped down further:

http://www.pbase.com/s​parksdjs/waterfront

Dave

Thanks for the help guys, off to Kakadu tomorrow and fingers crossed for some great shots,

Hal55