I don"t recommend you buy the lens of 18-50 f2.8 as it cost you about HK$2,850. I suggest you buy the lens of 18-70mm of Nikon instead of sigma 18-50mm f2.8.

The wide angle lens is used to take landscape photos mainly. As you pay money of $2XXX. Purchasing the Nikon lens may be more suitable.

But I don"t know what is the quality of Nikon lens 18-70mm.

My Canon 10D cannot use the lens of EFS 18-55mm.I have bought Sigm 18-125mm F3.5-5.6($1,650) for my Canon 10D. It is used for travelling photos taken.  

But the second hand value of Sigm lens is lower. I don"t recommend you buy the sigma lens.

I think you have to keep using the Sigma lens if you buy it. My Sigma lnes will not be sold out after my travelling. The second value of Sigma is poor unless the demand of lens is large (e.g.18-125mm)

So I prefer you to buy Nikon lens even it is expensive. If you don"t change other lens, just buy the Sigma lenses with cheaper value/price.

It is my second time using the Sigma lens. The first one is Sigma 21-35mm lens. I regret to sell it before as it is a good lens with least distortion.(The selling price is very low.....)

The Sigma 18-125 is not bad at all, consider it is just $1750.