why aren't all of the 10/11/12/14 - 16/20/24 zooms grouped together?

the 14-24 (and 24-70) are FX oriented lens, part of the 2.8 "pro zoom series" (14-24, 24-70, 70-200). on a DX body, the 14-24 becomes less of an ultra-wide angle, and the 24-70 becomes a somewhat less useful/optimal mid-range zoom.

on a DX camera, assuming you have something starting at 18 for the "all around" lens, i would ideally get one of the 10/11 starting ultra-wide zooms.

as for the Sigma, I borrowed it from a friend for a vacation. It worked well for me, though I don't think I'm advanced enough to really appreciate/notice the deficiencies it might have.

a review (which unfortunately pre-dates the release of Nikon's 10-24, so the comparison is to the Nikon 12-24):
http://bythom.com/sigma10to20.htm

and here's an example I took with Sigma 10-20, set at 10mm, aperture is f/7.1 (click the photo for a bigger image):



you can see softness/lack of focus in the lower right corner. f/10 would have been a bit better, but some of this is the nature of this type of lens. i'm looking forward to seeing some reviews/samples from the Nikon 10-24 before i decide to purchase oneof the ultra-wides for myself.

 

here's a review of the Nikon 10-24 from Ken Rockwell (his reviews typically feature a fair degree of hyperbole, so take with a grain of salt).
http://www.kenrockwell.com/nikon/10-24mm.htm

Her's a sample image (click for larger):



still a fair amount of softness in the lower right corner, though this was supposedly shot at f3.5, so could be a nice improvement over the Sigma at f/8 or f/11.

 

Horrible example.....

Here is a better one....

Sigma 10-20mm @ 10mm.....



Keep your eye on the bolt and text in the lower left corner...

No post processing other than converting to JPEG from RAW...



It's a phenomenal lens, in all situations, as LONG AS you know how to use it.

 

would appreciate if you could elaborate on what makes my example "horrible"... i'm here to learn as well.

 

For me personally, I don't like the palm trees at all. They ruin the play on the lines and exaggerated angles of the buildings.

 

It's not a horrible picture. It was a horrible example of a lens' sharpness.

On my example, you can clearly see sharpness, yours too busy. That's all I was saying.

 

Tamron 17-50 is a very nice lens. I own the latest version and I'm very satisfied with the IQ. The AF is not bad either, but Nikon's pro level AF blows the Tammy out of the water. Not sure if Nikon's 17-55mm AF is as fast as their 70-200mm, but if you don't need the instantaneous AF, then the Tamron is a good choice.

If you do go for the Tamron, either get the screw motor AF or the latest one with VC. Skip the one with built in AF and no VC.

 

Get the tamron 17-50 2.8 It is probably the best bang for buck lens I have I would also recommend picking up an 80-200mm nikon for it's value. Nice bokeh and if you get a good copy, sharper than the 70-200mm replacement

 

Oh, and I also shoot a sigma 70-200mm macroII and I like it but it is a hit or miss with those lenses, some copies are sharp and quick and accurate and others aren't so if you go with the aftermarket brands, buy from a place with a great return policy

 

I have the regular NON-VC Tamron 17-50, and it's one of, if not THE, sharpest lens I own, and my lens collection is pretty substantial.