Andaman Sea Blackwater

gokhankuzu wrote:

I do. I've dived hundreds of times at night, capturing moving objects. If something is wrong, it is wrong, it doesn't change the right that many people do wrong.

Wonderful! I'm sure you'll be happy to post some examples of your work... right? Right?

Objects that move after focusing do not stay in focus in DOF until the moment of shooting.

That depends on how much DoF you have and how far the objects move. If, for example, you have a two-centimeter range in which objects are sufficiently in focus to look sharp on the resulting image, then a one-centimeter move will not register. If, however, you have a one-centimeter DoF, and the target moves by that same one centimeter, it will, most likely, pass out of your 'acceptable sharpness' range.

High ISO won't help you freeze the image. 100 iso and 100000 iso freeze images with the same success. High iso only helps to make background images more distinct and you do not have such a purpose in blackwater shooting. TTL always works well at ISO 100.

An image is frozen when the flash light hits the object and therefore the sensor. If the speed of the moving objects is more than the shutter lag, blurry will occur behind the image. The only thing that matters is the shutter speed. There is no reason to do 160 instead of 200. If you can do HSS, you should.

That makes absolutely no sense. First of all, there is every reason to shoot at 1/160 rather than 1/200 - my camera syncs with strobes at up to 1/160s; at 1/200s or higher I'll get a black exposure. A cursory check of specs would tell you that. Yes, I can use HSS (uncommon underwater, but I happen to have all the required pieces), but this will drop strobe power considerably, far below that which is needed to shoot at small apertures (see above for the need to use small apertures for DoF buffer). Additionally, I want to have my strobes recycling quickly, so that I can use burst mode on moving subjects - taking half a dozen shots, maybe one or two will be in good focus - this limits available strobe power; using Retra Pro strobes with superchargers, I can do 3fps at up to half power. As an aside, I might add that this is considerably better than most underwater strobes. This, in turn, drives the need for higher ISO than baseline, as low power flashes at small apertures will not give a good exposure at baseline ISOs.

However, just for shits and giggles, I have taken some examples of blackwater images at a relatively open aperture and baseline ISO. Most of them look like this:

In case you were wondering, that's a squid.

Some are a little better, like this shrimp:

At the time, I didn't even know I was shooting a shrimp - I saw a tiny dot with two whiskers and took a burst of shots to figure out later what it is. At f/32, the body would've been in focus, not just the antennae. At f/11 - well, you can see for yourself.

For another comparison, here are a few squid that are in focus:

I challenge you to find them "four times sharper" than the ones in OP that were shot at ISO 800 f/25.