Ralph III wrote in post #16608951
1) A nice portrait lens.* This is what I reserved my Tamron 28-75mm for. I would like to maintain a high degree of IQ (such as my 15-85mm delivers) but with excellent isolation/bokeh. So if I can replace the Tammy with something even better then great!
2) A versatile walk around lens. This is what I have reserved my Canon 15-85mm for. I no longer have a long lens though so I'm thinking about replacing the 15-85mm with either the Sigma 18-250mm Macro or the soon to be released Sigma 18-200mm, if reviews are good.
Yes, I may suffer some IQ loss but I hope such can easily be fixed in post processing. I will use my Portrait lens when the greatest of IQ is desired.
I've thought about fixed lenses but it's hard to chase our little girls around with such, having had two nifty fifties but selling each. Maybe I can give another fixed lens a try? Or maybe I should consider such as a 17-50mm 2.8? Does anyone have any experience with the Tamron 17-50mm f2.8 XR Di II LD lens?
1) Get a good prime instead of a zoom then. 35mm F2 IS, or 85mm F1.8. All the isolation you need. Pick the focal range that suits you (normal view, or telephoto). They can both isolate. It just depends on your setup and if you're doing it indoors, outdoors, etc. The closer you are with the 35mm, the more isolation. Same thing with the 85mm, but you still have more distance between you and the subject with the 85mm. If you're ok with getting within a few feet of your subject, the 35mm if very nice. If you want to be further away, like 10 feet or so, look to the 85mm. Get both maybe. I use these for portraits on a crop. Both full body & portrait. Great focal lengths on a crop for this. I wouldn't trade them for a zoom, at all. At least, not one that doesn't cost $3k basically. Even then, those zooms don't do F2 and F1.8.
2) Here's where you get your zoom. Get the 18-200mm. Covers all bases.