Andaman Sea Blackwater

gokhankuzu wrote:

You used flash first, then why iso 800?

Because when shooting translucent critters at small apertures, even powerful strobes don't have enough output to work reliably at ISO 100. As I understand it, ISO 800 is where the dual gain circuit on A6xxx cameras kicks in, so shooting anything between 100 and 800 is largely pointless (on blackwater dives; day dives have different considerations), as is any setting above 800.

Why is your f value 25? You may have wanted to make the background dark, there is no need to narrow the aperture that much.

Depth of field. This is a blackwater dive, conducted at night, in open water, away from a reef. The bottom is at roughly 80 meters (in this case); the only visual reference is a drifting line hung from a buoy with some torches on it. The subjects range from small (a few centimeters) to tiny (millimeters) and tend to constantly move in all three dimensions. AF-C tracking helps a little bit, but it only goes so far.

Quality decreases after f11. f25 and iso800 reduce the quality of the photo and reduce its sharpness.

It does, and they do, but missing focus on a tiny moving target reduces the quality far more.

You have a TTL converter, iso 100 always gives the best quality, the more you increase it, the worse it gets.

In TTL mode, output range of Retra strobes is somewhat limited. I was chasing a larval crab (a brown ball maybe 5mm in diameter) and as shots taken at f/25 kept coming out of focus, I tried to crank it up to f/32 for a little more DoF. Surprise, the next shot came out significantly underexposed.

Edit: Oh, and while some subjects are translucent, others are reflective, and some are both at the same time (e.g. translucent body with reflective internal organs). You're in mostly total darkness, so you can only see them while they're in your torch beam, and some of them are attracted by the light, so they swim at you, past the focus point of the lens, and hide between you and the camera. Others dislike the bright lights and skedaddle shortly after getting discovered, going much faster and deeper than you can follow. If you pause and start playing with your camera settings to get them just right, chances are near certain that the subject will disappear, and your perfectly set up shot will capture an empty field of plankton.