Barry Guimbellot designs DIY small dome port for CFWA 
Wetpixel member explores the close-focus wide angle dome design process for his Nexus housing
Last Update: 01 March 2010 10:10 PM
10 comment(s) | discuss in forums
Author: Barry Guimbellot
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.
Thats a great little dome you have there. Out of interest, what kind of cost did it come out at.
Stew
Posted by stewsmith on 03/01 at 02:05 PMNice article and a great invention.
You had better get ready for lots of orders.
Don
Posted by Don in Colorado on 03/01 at 04:26 PMGreat article and ingenious solution. Looks good too!
Posted by Arne on 03/02 at 05:47 AMThanks for the compliments!
As for the price Stew, I have worked a deal where I can sell some at $360+shipping, which includes the lens shade and a small allen wrench.Posted by Dupsbear on 03/02 at 11:39 AMCongrats Barry and great job! That’s not easy to do and I appreciate the amount of work you put in. I haven’t been following Alex’s articles on using the 10-17 w 1.4 so may be repeating things. will look those up. What exactly are the benefits over shooting the lens w/o the teleconverter. I am using 10-17 with the Sea and Sea Optical Glass dome and can focus to the glass.
Andy
Posted by asallmon on 03/03 at 10:54 AMHi Andy,
Thanks for the compliment!
I used the 10-17 with a teleconverter in the Philippines to get some great cfwa of 3” long nudibranchs, but still have the DOF to render a diver in the background. The teleconverter is great when you want to make your foreground subject very large, but still gives enough room to light the subject.
I also used the teleconverter in Cozumel when I wanted wide angle but did not want the image too wide. As matter of fact, I am now using the teleconverter more than without, except when I want to go really wide like in a cenote or on a shipwreck.Posted by Dupsbear on 03/03 at 11:01 AMAndy, I posted some images in the forum topic about my mini dome with some images showing the benefit of using the teleconverter.
BaryPosted by Dupsbear on 03/03 at 11:34 AMHello Barry,
Despite loving this style of image, I don’t think I fully understand the advantage of this combination, would you be able to explain the difference between the 10mm and 1.4 combo, versus just using the 17mm end?
Thanks Mary
Posted by Mary Malloy on 03/10 at 03:48 AMHi Mary,
In a nutshell, more working distance. Using the 1.4X TC gives more working distance when shooting timid creatures or if I don’t want to get too close. The working distance also gives me room to get my lighting where I want.
If I am not going to need the 10 mm coverage, I put on the TC. Sometimes, the 10 mm end of the lens is just too much, so using the TC gives me the full range of the lens, instead of only working the 17mm side.
Using the 10-17 Tokina with a TC gives me more of the angle of coverage I loved with the Nikonos 15mm, but now having a zoom. I posted some images in the DIY forum about my mini dome as well as on my site at http://www.creativeillusionsphoto.com/portsale.htm
I hope this helps,
BarryPosted by Dupsbear on 03/10 at 07:01 AMBarry,
I am just shooting wa Canon 17-40mm, but will want to get the Tokina and your port as well.Can you email me at with your pricing and availability?
Thanks
EddiePosted by EddieM2750 on 04/03 at 09:27 AM
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