Ivoire - thanks for the compliments. The Sigma 180 was bought primarily for use as a macro lens with long focal length. I'm a keen fly-fisher, and also like to try and take macros of many of the water bugs and insects we try to mimic with artificial 'flies'. They are very skittish, hence the long focal length. I already have the Tamron SP90 macro, but that needs to get too close. Used as a general purpose 180mm tele lens, it works just fine. It does have a focus limiter on it, so focus travel is not excessive, but as the lens is so big and heavy, I wouldn't recommend it as a prime tele just for the occasional macro. Perhaps the Tammy or Sigma 70-300 or the Pentax 55-300 would be a better bet for that?
Peter Zack - what can I say? That explanation is fantastic - thank you! Your post is duly cut and pasted and printed for reference. I'll try that method next
It's 06:25 here in Brisbane, and the sun is not yet up (it's our late autumn/fall, only a couple of weeks to go till winter, for all you northern hemisphere types) but I'll be out trying more with this lens later today. I'll try the ImageShack method of posting if I get some decent shots.
What a great resource for help and learning all the folks are here on PF - thank you all