Ok so its time to start thinking of going wide with things and getting into wide angle work! I was originally going to get a sigma 10-20mm f3.5 (its price over the f4-5.6 is not much higher so I'd rather go for the option of constant aperture optics). Reviews I've read (in addition to the below) have always stated that the sigma 10-20mm retains a high level of optical quality whilst also being slightly cheaper than the canon and other market options. Juza Nature Photography However sigma have released a new 8-16 f4-5.6 lens that looks somewhat interesting for getting into ultra wide stuff without going fisheye. I've heard and read less about this newer, and higher priced lens though it appears to get some very good reports: Juza Nature Photography Especially with edge sharpness and quality. At the moment I only have my 18-55mm kit lens (that I generally don't like using) so the ultra wides will offer me something more than I can currently do. I also plan on having a 24-105mm in my setup so, unless I get totally addicted to wide angle, that means a difference of either 20-24mm or 18-24mm depending on which option I go for (unless of course someone suggests another wide angle lens option). So what are peoples thoughts here about these wide angle lenses? Also - if anyone has used any of them with extension tubes I would be greatly interested to hear the results.