Please Read because some of the information above is a bit incorrect. First the Sony A7 line of housings has an N-100 100mm port mount not N-85 so any comparisons are not valid. Using the Nauticam N100 to N120 35.5mm port adapter allows you to use N-120 ports and in the case of the Canon 8-15mm Fisheye the metabones adapter extends to the edge of the port adapter and then you use the Nauticam Canon port charts to find the extension for the 8-15 zoom. The proper extension for the 8-15 zoom is the N-120 30mm for the 18811 140mm fisheye port with removable shade and 30mm for the Nauticam fisheye port II and 30mm for the ZEN 230mm. Both have dome shades that can be removed for use at the extreme 8mm end of the lens. Be aware a 140mm port is made that does not have the removable shade. Zen also makes a 100mm with and without removable shade. The ZEN DP-100-N120-CR (For removable) would be the proper dome.
The Zen 170mm and Nauticam 180mm ports ARE NOT fisheye ports and DO NOT have removable dome shades, so the 8mm end of the lens would be useless unless you crop out a good deal of the frame.
I have used all three port sizes extensively and as you would expect the larger the port the better the image quality in the corners with apples to apples settings.
I would agree that the 230mm dome is a bitch to travel with but I have managed to keep my carry-on roller bag to under 12kg by putting the housing without grips, lenses and bodies into my "computer" second carry-on bag. The larger upside to the Nauticam/Zen 230mm (I own the ZEN) beyond the obivious over/under upside is that the230mm port can be used with the Sony 12-24 zoom, 16-35 F/2.8 & F/4, Zeiss 18mm and more by using 20mm, 30mm and 40mm extensions.