I’m seriously considering buying a fisheye lens for my Nikon D300. At this stage I have it more or less down to a choice of two – the Nikon 10.5mm and the Sigma 10mm. Both are 2.8, and the Sigma has the added HSM focusing. Apart from this the Internet seems to have limited customer reviews on these lens.
Does anyone have experience of either of these lenses or offer any advice please? 
Thanks.