I've been on two trips to Cocos (one was to Malpelo as well)...
The first time I shot exclusively w/the 12-24 (w/a D200) and I wasn't really thrilled w/the results.
In Malpelo the water tends to be a little murkier, and the hammers a little more distant (mostly because there are fewer places to hide behind and wait in Malpelo). The "eel condos" at Malpelo (multiple to many eels in one hole) are great subjects, but shooting them w/the 12-24 also means you get some of the soft edges in your pictures (not shooting against a water background)
The best results on that trip came from someone shooting w/the Nikon 10.5 - some really outstanding stuff.
My second trip (Cocos only) I brought along the 10.5 and the 10-17, and I ended up shooting the 10-17 almost exclusively - much better results than my previous trip.
Part of this I do attribute to the lens - the 10-17 was a great fit for most of the subjects (hammers, silvertips, marble rays, the plethora of white tips, and the occasional manta).
The other thing I attribute this to is that unless you have spent a significant amount of time shooting sharks in close, the first time to Cocos you really don't get a feel for how close you should be to get a good result. Between the surge, sea urchins, other divers in/around the cleaning stations, and the many beautiful hammerheads meandering by (all while you are likely holding your breath) it's (really) hard to get an idea of how close you need to be to get the really excellent shots.
Shooting w/the 10-17 (usually set somewhere around 12-14) it took me a few days even on the 2nd trip to realize that the best shots are going to be taken extremely close in (like within 5-7ft away from the hammers coming in to be cleaned). You're usually going to be hunkered down behind a rock (note the locations of the urchins - they are usually in the spot you want to be in
, and then managing your breathing until the last possible moment to take a shot (or two...).
Other lessons learned:
1. Shoot up (duh!) - the problem is that there are likely going to be hammers below you, but the background is dark rock/substrate so there isn't a lot of contrast to get an appealing image. You get so tempted to shoot the ones that look close (below you), but in most cases the resulting image won't be great (unless it's really close).
Note on "shooting up" w/the Marble Rays - maybe it's just my strobes (dual Z240's) but shooting a Marble Ray from above (w/out a real contrasting background like sand) was like shooting into a black hole - these things seem to eat up your light. Shooting where you can get some white of the underside of a marble ray is a necessity (from my experience).
2. The fewer divers on a cleaning station the more likely you'll be able to get close. It's not that everyone isn't trying to control their breathing, it's that eventually everyone has to exhale. This means that while you're holding your breath the person to your right/left or above you will likely be exhaling, thus keeping the hammers a little farther away.
My favorite spots were the 2nd and 3rd cleaning stations on the backside of Manuelita. While the rest of the group was hunkered down at the first cleaning station, my buddy and I would head off to the 2nd or 3rd spot. With only a couple of us there, the hammers came in really (really) close (I had one or two that I could have touched as they swam straight over the top of me).
If you're diving a rebreather you can practically sit in the middle of the cleaning station and not scare the sharks away (the sub pilot, Smulek (sp?) did this a couple of times - amazing images).
Alcyone is another great spot - but it's harder to get underneath & close to the sharks here (and it's deep). Great place to get the "schooling hammers" image though...
Damn - just writing about this makes me want to go back - I'm trying to talk the wife into letting me again next year. I'm hooked, it's such a unique place...
- Matt