I taught my annual Digital Master class in Key Largo last week, and having six days of local diving provided a bit of time to test new gear. One item of significance was the new Sigma 20mm F-1.4 prime wide angle. I shot it on a Canon 5Ds, SEACAM housing, Superdome, and 57.5mm port extension. This is the same one I use for my 16-35mm lens. I did not obsess over what port extension would put me in exact nodal point of the lens. Rather, this is simply plug and play with gear I had easily at hand. Here are the results:
Sigma 20mm lens on Canon 5D3 for scale
Normal perspective of 20mm lens underwater, chosen to illustrate primary subject on same plane of focus as background
Test of near focus, with seafan lower left actually touching the Superdome and zone of AF on this portion of seafan
screenshot at 100%, corner detail lower right
screenshot at 100%, corner detail lower left
screenshot at 100%, detail close focus on seafan lower left
In that this lens is Sigma, it can work either Nikon or Canon. I find great potential here and bring it to your collective attention due to collective angst over poor corner resolution in many wide angle optics used UW.
