Sigma 18-50 f2.8 vs Tamron 17-50 f2.8, better optics?

[carlos_rodriguez3]

<p><!--

<td width="280" >18-50 F2.8 SIGMA DC D EX MACRO (72)(APS-C) WITH HOOD, CAPS, DIGITAL SLR ZOOM SUPER WIDE ANGLE LENS--><br>

First question:<br>

Which one will have better optics?:<br>

Sigma 18-50 F2.8 DC D EX MACRO<br>

Tamron 17-50 f2.8 Xr Di-ii<br>

Second question:<br>

Will they work AF in a Nikon D40x?</p>

[hans_janssen]

<p>The tamron is a very good lens and I believe there is a BIM(build in motor) version available. You need BIM for a D40.</p>

[ian_murren]

<p>I purchased the tamron at work (for someone else) because of its reputation. I tried it out, took a few frames, I was surprised the difference between 17mm and the 18-70's we have around. That extra mm is surprisingly wider. </p>

[krisheylen]

<p>I've been spending all week to compare the two, and I've read all the comments I could find. I think you couldn't go wrong with either.<br>

The main differences:<br />- The Tamron is a bit wider.<br /> - The Sigma focuses at 20 cm while the Tamron focuses at 27 cm.<br>

I decided for the Tamron, which should arrive tomorrow.</p>

[kris-bochenek]

<p>I own Tamron and use it on my D300 it's a great lense I cannot speak for Sigma but I can tell you that Tamron is a one good lens.</p>

<p>Regards</p>

[eric_arnold]

<p>hi carlos,<br>

i personally opted for the tamron, as it has a somewhat better reputation. i have a friend who had the sigma, it was pretty good optically too. the sigma has HSM, so it's probably a little faster to AF than the tamron's BiM. neither is really a 'macro' lens, though the sigma is a little bit better at close-up range. 1mm extra on the wide end does make a difference, and FWIW, I shoot the tamron at 2.8 a lot and find it's very sharp wide open. can't really speak on the sigma.</p>