Here's the story. I pursued a photojournalist career while I was in high school and up until I graduated with a journalism degree. Then I changed careers. I know-- goofy. Anyway, I started in Nikon since most PJs were shooting Nikon and I've stayed with Nikon since I don't burn Ben Franklins to heat the house. It would cost a lot to change to anything else (not that i want to). Nikon is arguably one of the best optical companies on the planet and the availablity of used stuff is really good. I have traded most of my manual focus stuff off for AF. I don't shoot dit yet and probably won't until the aspect ration of lenses is 1:1 for SLRs and the price comes down another $1k. Today the D100 is a 6.x megapixel camera for $2k so things are getting to my price point. But the lens ration is still not 1:1, so i wait. To fill the gap, I bought a Nikon Coolscan 4000 film scanner to scan slides and negs so I can do this pesky website.
My basic setup is a Nikon SLR camera system in an underwater housing. I chose to go the housing route because I already own a decent camera system and couldn't justify an entirely new system i might use twice a year (if i'm lucky). Also, the housed system gives me the advantage of using the advanced features of the n90s body. Features like autofocus, multi-segment ambient light metering, and TTL flash are a few.
The drawbacks of the housed system are physical size and additional considerations like focus lights to help the autofocus work in dim conditions. Also, if there is a lot of particulate matter or small animals (real small) in the water, the AF system will try to focus on them sometimes. This can be overcome by rigging manual focus, but i use AF exclusively and deal with it.
I bought the housing and two lens ports used from an Internet contact. The lens ports are changed depending on the lens on the camera. The dome port is for wide-angle and the straqight port is for macro and short tele. I got all this for the cost of just a new housing. It works well, except the lens ports are a little scratched and dinged. i can see the imperfections when shooting into light. Ports are relatively cheap ($150) so i will probably be replacing the dome port soon.
I use one 200 watt/second strobe. This is a powerful light and does work extremely well in macro situations. I actually think macro is easier to shoot technically because the lighting considerations are generally easier. you don't need to consider ambient light at all in most situations, just stop way down for depth-of-field and compose, etc. However, the light won't go as far as you think and picks up a lot of backscatter (light bouncing off particulates in the water creating a snow effect) when trying to light subjects that are more than a few feet off. The TTL lighting system between camera and strobe generally works well. However, as on land, this system can be easily tricked with high contrast scenes. I would like to try housing my SB-28 and getting full Matrix fill flash capability underwater. This setup has rarely missed on land and i think it would take some of the guesswork out of balanced fill flash. On land, whenever there is any question about the fill light, i bust out my hand held meter and check all my readings. Since I don't have the equipment or the luxury of time underwater, i think the housed SB-28 might be the solution.
I started out my U/W with a 20mm 2.8 and the 60mm macro. The 20mm I use for wrecks and close focus wide angle with strobe lighting in the foreground. The close focus is tricking my TTL (see above) but the 100% ambient with the wide-angle is working well. I traded out my 60mm Micro for a 105mm MIcro. The 105 will focus closer, rendering a larger subject and will also allow more distance between the housing and the subject. A lot of fish disappear when a big ol' lexan housing comes their way. A 105 should help that.
U/W photo has changed the way I dive. Now, I prefer very slow moving dives so I can study the subject matter closely, especially when I have the macro on. Night dives in a no current reef are amazing for macro photography. Go slow and if your buddy is not a photog, maybe they can help you find subjects on another section of reef.