alright, you guys are confusing me in several ways
First, why would you want to use a dome port for macro? The basic idea of the dome is to correct two things 1) to correct for the 25% magnification you get with a flat port which makes your lens less wide and the idea of being as wide as possible is that to get the same size subject in the frame you can move closer thus reducing the amount of water you are shooting through and increasing both sharpness and color saturation. You also get the added benefit of reducing the effect of unwanted camera motion and your lights are effectively stronger because the light doesn't travel as far through the water so maintains more of its color and brightness. and 2) the dome corrects for some of the loss of edge sharpness and chromatic aberrations that happen with wides behind flat ports because the light rays from the edges of the frame are hitting the flat port at extreme angles whereas if properly aligned all of the light rays hit the dome perpendicularly.
One thing to remember though (that is important when we talk 3d) is that the dome creates a curved virtual image and some "fisheye" distortion. The problem with 3d is that the lenses can't be centered so any distortion is in opposite directions - and the images don't overlap properly.
Although we often shoot macro with zoom lenses through dome ports -because it is easier than swimming to the surface to change to a flat port - it isn't ideal. You generally shoot macro with telephoto lenses, so you don't have the problem of steep off axis light rays and you don't need to be 25% wider to get closer. You generally choose your shooting distance to macro subjects based on how close you can comfortably work - often a foot or less - so you aren't shooting through a lot of water.
So shooting 3D macro through a flat port is just fine anyway.
