hi, so i've decided to buy a canon 40D body and start my journey i'm very confident and excited to begin with the 40D. so, for a lens, considering i was new, i was immediately let down because i knew i couldn't afford the standard canon 2.8 l lens. so resorted to third parties - tamron and sigma. ulitmately, after hours of research, i went with the sigmas. i really wanted a lens that was cheap, had a 2.8 aperture, standard zoom. and then i found the sigma 18-50 mm. but i'm stuck between these two: 1: Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC Optical Stabilized (OS) Lens with Hyper Sonic Motor (HSM) Amazon.com: Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC Optical Stabilized (OS) Lens with Hyper Sonic Motor (HSM) for Canon Digital SLR Cameras: Electronics and 2: Sigma 18-50mm f/2.8 EX DC SLD ELD Aspherical Macro Lens for Canon Digital SLR Cameras Amazon.com: Sigma 18-50mm f/2.8 EX DC SLD ELD Aspherical Macro Lens for Canon Digital SLR Cameras: Camera & Photo my questions: is the price difference worth it? why the price difference in the first place? what's the "better feature" in the $420 one? which one has sharper image quality? which one? is the cheaper one w/o constant 2.8 maximum aperture okay to live with? i know, very vague, and this question is probably asked before, but any reply would be reat thanks.