Extension Ring for Sea & Sea D300

I just started using the Nikkor 12-24 F4G with a Sea & Sea D300 house with fisheye dome with NO extension ring. The system chart for Sea & Sea does not require it for that lens with the fisheye dome. Meanwhile every other lens suggests using an extension ring with the fisheye dome. I shot some pics to find that the corners of my images are extremely blurred. I am about to get an extension ring. Does anyone have anything to add to this?

Mike

The S&S chart is wrong. They messed up the chart for the 5D2 as well. They only have 2 extension rings. Not familiar with the Nikon 12-24, but you don't have a lot of choice with extension ring sizes with S&S, so try the smaller one first and use a diopter if things don't improve.

Hey Mike, use the extension ring 40 and a plus 2 diopter.

Mike