Sigma 24-70mm F2.8 EX Aspherical DF Lens for Nikon-AF Camera

Rating:
Summary: this is my primary lens for my Digital SLR
Review: I've used this lens for about 8 months and have come to love it. I keep it attached solely to My Nikon D100 for which I think it is especially suited. The "35mm equivilant" focal length, while on the D100 is 36-105mm which works quite well for me.
Key Points:
Strenghts:
1.)Consistant f2.8 max ap - this is a FAST lens in this class, giving me a bright viewfinder screen and making focus (auto or manual) faster and easier in dim light.
2.)Auto Focus speed - quite fast, especially given it's weight
3.)Sharp - especially at f4.0 or smaller. - note the fast 2.8 max is great for focus and composition, but there are no lenses out there that I know of that don't benefit from closing down at least 1 stop. Don't get me wrong though - this is great glass, and clearly worthy of Sigma's top-o-the-line EX designation. Edge of field sharpness - nothing to complain about here
4.)Color - really is great, likely benefits from the exotic glass.
5.)Focus Clutch - when in autofocus mode, push the focus ring to AF mode, which essentially takes it "out of gear" so you don't inadvertently try to overcome the lenses focus motor.
6.)Range - on my 35mm film SLRs, I use primarily a 28mm+ for wide shots but especially on a D100 or D1x, this lense turns out to have, for me at least , a great range as I get the "equivilant of 36mm given the CCDs chip size as compared to film. Note that especially with Digital SLRs the last thing I want in the field is a lot of lense changes to get dust in the camera and onto my CCD sensor (n fairness - not the sensor but the moire filter in front of it). I wish someone made a 20mm-70mm f2.8 but I think the chances of seeing that any time soon are small.
7.)Cost - look at other manufacturers, the same specs from nikon would cost >$1000 IF you could get it. And again, this is a great pice of glass, not just a great piece of glass for the price.
Issues to know about:
1.)Size - this is a big fat lens - clearly not that much fun to carry. Also the caliber of the lense makes access to the aperture ring difficult, so you'll clearly want to set and lock the aperture at minimum and control it from the camera front control wheel (on the F100 you have a choice, not so on the D100) if your camera allows that
2.)Filter diameter - the lens front filter thread diameter is 82mm! It took me a month to find a 1A filter in that size (Contax makes a nice one, ended up getting it at BHphoto)
3.)Resistance to zooming - going from ~30 to 24mm involves twisting the zoom ring a little harder - you are moving some big elements when you do this, and if you put the camera down, lens up, the weight of the optics will cause it to "collapse" ie to zoom back to ~50+mm
4.)Finish- this lens has a dull black finish which I like a lot - some people might want the polished or black laquer finish.
5.) Brand - not all Sigma lenses are great...but I think this one is. No apologies.