So after having my Alpha a couple of weeks, and seeing what I am taking pictures of, I'm feeling limited by light.

I really enjoy candid shots of friends, family, dogs, etc, in the house, without using flash. I have a flash, it works well, but its obtrusive, and I'm not skilled enough to take the pictures I want with it.

So right now I have the kit lens and the Sony 75-300 (which I may try to trade out for the Tamron, b/c it seems to be better for less money), but I'm going to try to pick up another lens. I originally was planning to get an older Minolta 50mm f/1.7, but from what I'm reading here, you guys seem to strongly suggest the Tamron 17-50 2.8. The Minolta would have a larger aperture and be a lot cheaper, but the Tamron would also allow me to pretty much replace the kit lens. I think I need a new paperweight anyway.

But to be pragmatic, my issue is low light, and I have a baby on the way so budget is an issue. So my question is mainly about how these lenses perform at higher apertures. If it turns out the Minolta isn't very usable at 1.7, and I'll be using a higher aperture most of the time anyway, and the Tamron is usable at 2.8, then the Tamron is obviously a better choice. But if the Minolta is going to allow me to reasonably use higher aperture and get the shots I want, I'll buy that one soon and pick up the Tamron later. How big of a difference will I see in low light shots between the two.

Thanks for any thoughts on this.