Nikon 18-70mm with which Ikelite port??

Here are shots from my first use of the Sigma 15mm FE with 6" Ike dome.

I'm very glad I went for the 15mm over the 10.5. And so far it seems to work perfectly behind the 6" dome. Fish eye distortion is hardly noticable underwater.

It's also a full frame lens so "future proof"

I usually prefer the brand name lenses but the Sigma 15mm is one exception.

True, the Sima 15mm and the Nikon 16mm are comparible.

However the main advantage of the Sigma is closer focusing. For WA many prefer the close focus wide angle technique and the Sigma will allow you ro get super close to your subject.

Alex Mustard likes to use teleconvertors on his 10.5mm to get super close focus macro shots of a subject and its environment. The Sigma 15mm is roughly the equivelent of the 10.5mm + a teleconvertor. The Nikon 16mm doesn't focus close engough for this exotic technique.

The re-sale value of the Nikon is better though. Both are rasor sharp.