Andaman Sea Blackwater

Oh, so you simply have zero comprehension of what I'm talking about... okay.

Blackwater dives are conducted at night, in open water, away from the reef or any other solid features. Depending on location, depths can range from a few tens of meters (I was diving over 78m of water) to kilometers (places like Hawaii feature some spectacularly deep drop-offs). Regardless, you're not expected to see the bottom at any point during the dive. Prior to the dive, a buoy with an attached 15-20m line is released into the water; the line has a number of powerful LED torches attached to it at regular intervals. The line is free to drift with the currents, and the illuminated buoy is used by the boat crew to track it. The torches serve two functions. One, they provide a visual reference for the divers - they are visible from a significant distance away, and help you to return to the group if you drift away. Two, the light serves to attract various small critters, which attract predators, which in turn attract bigger predators, and so on. This type of diving is notable for encountering the larval and juvenile forms of many marine animals that are pelagic early in their lifecycle, before metamorphosing into their adult forms and settling on the bottom. Likewise, you an encounter creatures that spend the daylight at significant depths inaccessible to divers, and migrate upwards in the water column to feed during night-time.

However, with everything being free-swimming, often transparent, reflective, or both at the same time, subject sizes trending toward the small and tiny, water being dense with planktonic particles, and anything outside your torch beam being completely invisible, difficulties in obtaining properly focused and lit images are... considerable. If you check out the blackwater diving group on Facebook, where many images include the settings at which they were taken, you will find that f/18~f/25 is the most common aperture range, for precisely the reasons I have outlined in my earlier posts. If you want to prove that most everyone shooting blackwater is Doing It Wrong™, and you're right - get a flight to Florida, do a few blackwater dives with any of the multitude of operators who are doing these dives over there, and post your work. No, images taken on a reef, or during regular night dives do not count - the challenges are completely different, even if you're absolutely certain that your imagination tells you they aren't.

It's very interesting. I have done a lot of open water diving but not open water dives as you mentioned. I dove under Oriskany wreck in Pensacola and did many buoy dives but not night. TTL is useless in those dives, focus light or torchlight will mislead TTL. But this is a night dive and the f value is definitely wrong and also iso value. You should take the photo the moment you focus on it. f8- max f11 and iso 100 will give you incomparably better results than f25 and 800.