Barry Guimbellot designs DIY small dome port for CFWA

I have been working on a project for several months that has worked out better than I ever imagined.  Marty Snyderman showed me the Tokina 10-17 mm lens he purchased and then let me try it on my camera.  Instantly, I was sold on the lens as wide angle photography is my passion, so I purchased one for myself.  After reading on Wetpixel about the luck Alex Mustard and some others were having with the Tokina lens and a 1.4X teleconverter, I decided to give the combination a try as well.

Frustration quickly set in as I found my large dome port would not let me get as close as I wanted for shooting close focus wide angle.  Even more frustrating was the price of a small dome port for my lens, so I decided to build a small port for my Nexus housing.

First, I researched the nodal point of the Tokina lens and then design what I thought to be the perfect ratio of port diameter and arc radius for the lens curvature.  A friend told me about a machinist company in Dallas, Kress Technologies that might help me with my design and machining.  Kress turned out to be just the company I needed; they are small but do some government work making them friendly, easy to work with and yet extremely competent.

I found a 20mm Nexus port extension tube that fit my housing and designed my port housing so it could slip over the extension tube.  My first design was machined out of Delrin after I found an adhesive (Pacer RX-GEL) that will bond to Delrin and aluminum.  I would have used aluminum for the prototype, but I found out how hard welding aluminum can be.

The actual dome turned out to be the hard part of my design with several purchases of prototype domes proving to be inferior quality, but finally I found a company that produces perfect domes for my design.

All domes are not created equal. Sigh…..

For my lens hood, I went to Home Depot and purchased some drywall tape to use for a fiberglass mold.  I then unwound the tape until I had my needed inside diameter and mixed my fiberglass resin with black plastic dye.  The job was messy, but I was able to wrap the cloth around my mold until the fiberglass was about ¼” thick.  After the fiberglass dried, a Dremel tool was used to shape my hood.  As one can imagine, there was lots of trial and error in getting the lens hood so that it would not vignette with the Tokina lens.

Before taking my port underwater, I put the port in a pressurized paint can from Home Depot, the same pressure tester I used when I did Nikonos repair. The port did not leak, so I was ready for the next dive trip.


My first prototype

What amazed me is the port not only works, but gives me sharper and more saturated colors than I was getting with my original port.  Not only are my images sharper, but there does not appear to be any distortion at the edges from the dome.  I shot some images in my pool, be careful to make sure something was in each corner. Another positive to the port is I could get within inches of a subject and not be shooting down.


Tokina @ 10 mm no teleconverter

Tokina @ 10 mm w/teleconverter

Both images are uncropped.