This dome shade solution is virtually free and sufficiently robust for most purposes, and much lighter than, for example, the aluminium dome shade on the Nauticam 9" dome.
The dome itself is an 8" hemispherical cast acrylic dome made for a marine compass.
It is glued to an acrylic base adapter that mounts to a Nauticam "10mm extension with screws". I use this dome for the 8-16mm Sigma and not a fisheye, which accounts for the size of the shade. For a fisheye, the shade would be much reduced in size.
Make a cardboard tube first and mount it to the dome. Mark the edges of what you can see with the lens at its widest setting while looking through the viewfinder to create the pattern.
The CAT oil drum is 2mm thick polythene and can be cut easily with a Stanley knife. I welded the edges together, not entirely satisfactorily, using a soldering iron and a stick of burning polythene.
Once burned, the drips are brittle, so it is better to melt the edges together without burning. I clamped a steel ruler to the join so it remained reasonably straight. If I had a hot-melt glue gun here, I would try preheating the edges with a blowlamp and using hot melt glue.
I used 2mm cap head screws and washers to fasten the dome shade to the acrylic.
