SCUBA diving



Although my first diving experience was in Brazil in 1992, I got officially certified in 2002 passing my open water exam at Dutch Springs, a flooded quarry in Pennsylvania. This first certification was PADI open water. In 2004 I got the PADI advanced open water certification, also at Dutch Springs. In 2005, as a farewell present from the colleagues of the laboratory where I did my Ph.D., I got the TDI Nitrox course. With that gift, I finally got Nitrox certified in 2006. From time to time I return to Dutch Springs to test my housings, or the modifications I do to them. It is a safe environment to experiment with new equipment.

PADI is a very basic company that seems more interested in making you spend money than in teaching SCUBA diving. I learned no serious theory at all with PADI. I did learn many practical aspects of diving from my instructor. In other words, my opinion is that all that matters is the instructor if you choose PADI as a certifying agency. I found TDI a bit better and less greedy. Although to be frank, if you are really interested in learning proper theory, don't expect it from any of these agencies. The courses are, understandably, designed to be understood by anyone.

Diving theory can be learned from many books. I found particularly useful the US Navy Diving manual (available as zipped pdfs). Another very useful article is the one written by Vlad Pambucol about dive computers (here). To learn a bit about diving physiology, I recommend the book Diving Science by Strauss and Aksenov. I also recommend reading about Haldane's decompression theory, Buhlmann's ZH algorithms, VPM and RGBM models to understand what your dive computer does when you submerge. A Matlab script I wrote with the Buhlmann ZH-L16 algorithm helped me understand what it is about. It is written in Matlab 6.5 Release 13 and it is here.

In the Travel, and in the Underwater photography page you will find photos of my diving trips.



Underwater photography



A recent hobby I have is underwater photography. More specifically, it is developing my own housings. The idea was pushed by the fact that I love to take photographs and to SCUBA dive, by the astronomical prices of underwater photo equipment, and by the lack of housings for Pentax cameras in the US. In Europe Nimar sells housings for Pentax, as well as other cameras, but the price is high, as it is for any housing. In the US, Nimar is hard to get and companies like Ikelite do not manufacture housings for Pentax.

I have a Pentax ZX-50, or MZ-50 depending on the region of the world. I wanted to build a dirt cheap housing from scratch so the PVC pipe housing was born. For detailed information about the project click here.

Although the PVC housing with the flat port went well to 90 feet (30m) in North Carolina without flooding, I wanted to get a dome port. A dome port eliminates, or reduces, the increase in focal length that is experienced by a lens behind an air-water interface. This “narrowing” of the effective acceptance angle is due to the difference in refraction indices between air and water. Using a flat port in an underwater camera housing increases by approximately 33% (the refraction index ratio) the focal length of the lens used. In other words, in a SLR camera a 35mm wide angle lens will become effectively a 46mm lens (almost a normal lens). To prevent that increase in focal length one can compensate by curving the port, and that is why dome ports are used in underwater photography. I got a Sigma 24mm f/1.7 macro lens for my Pentax and decided to house it behind a dome port. The best (economically speaking) option I founds was to buy and old Ikelite camera housing with a dome port and modify it to fit my Pentax. For detailed information about the project click here.

The next step was to bring out the color in the pictures. As you may know, water absorbs light unevenly. It absorbs more efficiently the red end of the spectrum (absorption spectrum here), and that is why everything looks blue once you are several feet underwater. A bright red sponge looks greenish-blue at 60 feet.

The idea behind carrying a bulky strobe light is to bring sunlight with you, and shine it at the proximity of the object to photograph therefore exposing its "true" color. I wanted to get around 100 to 150 watts-second of power so I decided to use two of the very robust Vivitar 285 flashes (pdf manual). I got, for 10 bucks on Ebay, an old Sea and Sea case that used to hold a video light. I then installed a new o-ring on it. I housed the circuitry of the flashes inside the Sea & Sea “box”, and used Ikelite ICS connectors to connect the two Vivitar flashes to my camera. The trigger circuits were wired in parallel. That was not an issue because my Pentax model can take up to 600V in the trigger circuit and as the two flashes were identical, that posed no problem for them. You have to be careful with this things because older flashes used to have high trigger voltages that not all modern cameras are able to take (Canons in particular). Anyhow, these paragraphs are only to say that it can be done. I did it and it worked very well on land during preliminary testing. The light sensors of the Vivitar flashes were housed in a little PVC pipe attached to the side of the dome port of the housing. The sensors connected through wires back to the flash housing using Ikelite connectors. Unfortunately, I did not realize that the Sea and Sea housing I bought for 10 bucks had a tiny crack that became a leak source at 145 feet (44m) when I was diving the Blue Hole in Belize. In summary, the flash project was promising and could work but flooded in its first dive. I could not get a suitable housing to repeat the experience and just before the diving trip that followed I decided to buy a used Ikelite Substrobe 200. That strobe is awesome! Some modifications have to be made to adapt the Pentax TTL circuitry to the Ikelite strobe. For detailed information about the project click here.



In addition to the housed Pentax system, I played around with Ingrid’s Sealife Reefmaster camera. This is a good system for those not willing to carry around a ton of equipment. It faces, however, the same problems than housed systems. Proximity to the subject is key to improve sharpness, and an external flash is required for decent color. The lens that comes with the camera is a bit narrow for my taste, something that can be worked around by using the wide angle attachment. Finally, the built-in flash is useless for purposes other than triggering an external flash. I believe the Sealife Reefmaster is capable of decent results with a wide angle attachment, 2 external strobes, and a lot of practice. Unfortunately, such a small system does not provide flexibility in terms of focal length, focusing distance, exposure time, and aperture.

In synthesis, with my limited experience, the conclusion is that nothing beats a housed SLR with one or two decent strobes. In addition, after using a 200 W/s strobe light, I don't think that getting something smaller is a good idea.

By comparing the underwater pictures of the different dive trips (below), you can see how much the dome port and strobe impacted the quality of the photos for the housed Pentax system, and you can also observe the effect of the external strobe for the Sealife Reefmaster camera.