So, I'm preparing for the upcoming trip to Prague and I've been all over the map with my lens choices. Lately, I feel less and less inclined to carry a large camera setup. I don't mind having extra lenses in a small bag if needed, but I really, really don't want to carry anything large hanging on my neck for several hours at a time. Also, I just took my kids to a technology museum last weekend, and in many situation the 18-105 was just too tight (it's FOV makes it more like 19-110). On more than a couple occasions I wished I'd have my 16mm with me. Anyway, I was thinking of buying a 20mm (15mm with UWA adapter that I already have) but it seems kind of pricey... Sigma 19 is great but wrong FL for me... 1855 is good but not wide enough... and so I keep coming back to thinking about 1650. From all the reviews that I read, 1650 seems to be as sharp or sharper than 1855 in the center, and slightly less sharp in the corners. My black 1855 is very sharp in the center, and my old silver one was equally sharp when it focused... which didn't happen all the time. The FL range is great, the size is great. The prices lately are low - there's a brand new silver one on Amazon for just over $100. So, how bad is this lens wide open at 16mm ? Or stopped down to f4-5.6 ? Is there going to be a noticeable difference vs 16/2.8 ? What about 20mm vs 20/2.8 ? Should I try it or will I be disappointed ?