lenses for rebel xt -2

[mediyoga]

28-105mm F2.8-4 ASPHERICAL IF
24-135mm F2.8-4.5 Aspherical IF
24-70mm F2.8 EX DG MACRO
Hi all
Need advice on these lenses. Any comments? particularly on
1) possibilities of low light focusing problems
2) quality of images
3) use these instead of my current 17-85 IS canon I dont mind giving up IS if these lenses are any good
thanks to all
Krishna Raman

[Rex914]

The quality of the first two lenses is very questionable. Your current 17-85 is a lot better than these lenses.

Lens number #3 is good if you get a good copy, but have you considered the Tamron 28-75 f/2.8 instead? Better lens for about the same price.

[mediyoga]

Thanks Rex. Here is a link to the sigma 24-135, Dont know if you have seen it.
http://www.dphotojournal.com/digital-slr-camera-lens-test-sigma-24-135mm-f28-45-aspherical-if/2/

I saw the tamron at a local shop seemd good. However a review at Miranda says that
"after taking plenty of pictures with it, I noticed that I had a high percentage of missed shots - my subject was very blurry. So I did what I never did before - I tested the lens. I found that wide open, wide angle, at over 10-15 feet, this lens couldn't autofocus worth a d*mn. However, I knew it was optically excellent because the few correctly focused shots were great, and I could use the parfocal technique to get correct focus, then zoom out.

I compared it against my other 5 lenses (all canons), and none had a focus problem, except for the 50/1.8 (only wide open). So I sent it back for the infamous "calibration." I got it back, and to make a long story short, the problem was still here. In fact, I did even more exhaustive testing than before and I discovered this lens has focus problems wide open, wide angle at *all* subject distances. When closed down to about f5.6 the depth of field increases enough to make the subject always in focus. But I paid for an f2.8 lens, not an f5.6 lens."
The other reviewers did not have this prob.Maybe this person's lens was a lemon?
Two more queries - can one fit a wide angle converter to the 28-135 canon lens?
can one fit a teleconverter to the 17-85 mm IS?
Krishna