I got all my parts from B&H. Im quite proud of the deal I got, everything in this picture cost me $290! The 8" dome alone was $450 before it was discontinued. These were all parts for a medium format underwater housing.
I had no idea the pieces would be so huge, from the pictures I saw, the port openings looked to be about 5". The port extension (with the blue tape) is what I'll use for my camera housing. There is a flat port for macro work, and a domed port for wide angle, both are designed to attach to the port extension.
After cutting off the threaded ring on the extension port with my table saw, I used a left over piece of granite from my bathroom counter and some sand paper to sand the sealing surface flat.
I routered an 8" diameter groove, 1/4" deep in a square piece of 3/4" plexiglass. The port fits snug inside this groove. I siliconed the cover in place, then used a router to trim the edges to give the plexiglass a smooth round edge.
I set up a jig on my router which used the housing as a guide to cut the plexiglass
Worried the silicone may not hold up, I drilled and tapped a bunch of holes to attach the rear cover, and installed an o-ring in the groove.
I can see the o-ring is evenly squished. I lubricated the o-ring with silicon grease.
I bent a piece of plate aluminum to match the curvature of the port, and welded some square tubing to make a handle. The hose clamps are used to hold the handles to the port, and to hold the two weight bags at the bottom. Im using two 3lb weights with no camera or lens in the housing.
On other SLRs I've used, I was able to connect a magnetic reed switch to the remote trigger input, and this worked perfectly. Unfortunately, the camera I want to use now does't have a trigger input (well, there is the magic lantern hack to covert the mic input into a remote trigger, but I didn't want to go that route). Anyhow, my solution was to add an RC servo to push on the shutter button whenever I trigger a magnetic switch with a magnet.
Servo pushes on the shutter button.
Back side view. My plan is to shoot video, and if I want to take a snap shot I can trigger the servo with a magnet. I have a huge knurled 1/4 20 bolt attaching the camera to the plate.
I have an underwater housing for a 580ex flash, it will be triggered with the ST-E2 IR transmitter on the camera. I'll likely need a fiber optic cable for reliable operation.
The lens sits well centered, with the lens face at the opening of the dome. I'll have to paint the sheet metal flat black to avoid reflections.