I have owned both len the 17-55, the 15-85 and also the Tamron 17-50 /2.8.Review your photos and track your aperture history. I have had everything from a Sig 30 f/1.4 to a Canon 200 f/2.8. I did not need a fast lens at this range. But I wanted a leave on, tote aroundlens. This new 15-85 is heaven sent for my needs. Some notes


<span style="color: #0000ff;"]Canon 17-55mm f/2.8 IS
  • <span style="color: #0000ff;"]as advertised .... v nice build, USM, IS, sharp - vg at 2.8, exc at 4..... but I sold because of:
  • <span style="color: #0000ff;"]indoor at 2.8 nice but you will not use all the time because ofshallow depth of field
  • <span style="color: #0000ff;"]disappointing, inconsistent low light shots
  • <span style="color: #0000ff;"]little heavy on my XSI,
  • <span style="color: #0000ff;"]too expensive for my wallet to tote around as my gen purpose lens



<span style="color: #0000ff;"]Tamron 17-50mm f/2.8 XR Di II Lens
  • <span style="color: #0000ff;"]very happy with package - sharpness, size, great value
  • <span style="color: #0000ff;"]sharp- gd at 2.8, but generally stopping down tof/4 vg/exc - sharp as Canon 17-55mm f/2.8 IS
  • <span style="color: #0000ff;"]where is the IS? once you've been stabilized, its like cheating (new IS coming out but may not be such a value)



<span style="color: #0000ff;"]Canon EF-S 15-85mm f/3.5-6.5 IS
  • <span style="color: #0000ff;"]extremely happy with package - sharpness, size, range, IS, value for $exc
  • <span style="color: #0000ff;"]touch lighter, inch shorter than 17-55 - better weighted for my XSi
  • <span style="color: #0000ff;"]nice indoor low light, I don&rsquo;t miss 2.8/ 4 (not trying indoor action)
  • <span style="color: #0000ff;"]don't have to stop down - sharp results wide open (of course wide open might be 5.6!!
  • <span style="color: #0000ff;"]But here's the deal for me: getting results assharp as any other, and, reliably consistent results
  • <span style="color: #0000ff;"]the range (on both ends) will totally spoil me - I&rsquo;ll laugh at 17-55/2.8 24-105/4