Question 1. (of many to come) Lenses For Nikon D100??

My experience with the 15-30 was that the lens vignetted at 15mm when the lens cover was left on except for the cap. It seems odd that Sigma makes their lens cap that way, but I believe Sigma does not intend that it be used as a filter mount. Instead, Sigma provides a gel holder.

The difference between Canon at 1.6 and Nikon at 1.52 is enough to hide the vignetting, so I think tha answer is actually different for the two.

NWDiver, I think the previous posts were referring to the 12-24 with a FUJI S2. In any case:

I have never had any problem installing or taking off the zoom gear on the lens, installing it on my D100 in the Aquatica housing, and adding the extension ring and the 8"dome.

It's a great fit, no forcing, no straches and it's easy!

I am very happy with it and it works really well for me.