About the choise of aparture and shutter speed with TTL

Hello,

He we go, between all the complex problems of digital underwater photograpgy, I would like to see how you chose the two major basic settings: aparture and shutter speed.

I am using a D200 with SB800 flash, on aparture priority, TTL.

What I think to know:

small DOF: low f (2.8) , larger DOF high f (up to ?)

daytime dive, to get the remote background in: slow shutter speeds (up to 1/10th), so high f. For exemple wrecks or 'hammerhead wallpaper' style pics.

Let's say I want to isolate a subject on a rock. Small DOF will help. But also high f as to limit the light from the surroundings coming in ? Seems contradictory. Also TTL will interfere adjusting the flash power.

Could any of the pros make a beginner general settings guideline for day&nighttime flash photography?

Please forgive me if asking to basic questions, but I see so many different settings used ...

Sven.

Try 1/125 f/8 @ 200ISO (flash on TTL).

If your pictures are over all too dark - increase the ISO and vice versa or open or close the aperture to suit. (Remember f8 = 1/8 of focal length and f11 = 1/11 of focal length. ie bigger number = smaller hole.)

If the background is too dark use a slower shutter speed (1/60 or 1/30).

If the background is too light, get a more powerful flash and start at the beginning with a smaller aperture.

I think that, if TTL is working you should not worry about the flash (it will iluminate all right as long as we are not talking WA). Shoot manual! no priorities just yet.

You have several ways of limiting from the surroundings coming in:

ND filters (I don´t think it applies here...)

Lower the ISO (can only lower it to 100)

Max speed (only to 1/250 because of iTTL synchronization)

Once you have tried this and you still get light from the surroundings you can only use a higher f at the "cost" of more DOF...and this is when your personal compromise should choose. I recommend you go next dive and choose an static eyeless subject and start a series with f 2.8 all the way up. Then, in your computer, you can make up an idea of what is best for your likings...

i agree with davichin about not using priorities to shoot. for underwater, you are almost always going to want your shutter speed to be between 1/30th and 1/200th (or your flash sync limit). what i do since i ussually prefer a darker background, as i mostly shoot macro, is i set my iso at either 100 or 200 depending on how bright it is (100 for sunny, 200 for cloudy), and then i set my shutter at 1/125th. then i shoot like i am in aperature priority. with the ttl, it will give you the needed amount of flash to properly light the picture (only case is if you are shooting at a large aperature and slow shutter speed, you may get a blown out picture if its bright outside). i just set whatever i want my DOF to be, and shoot away. if i decide i would rather have a darker or lighter background, then i will adjust the shutter speed (bump to 1/30-60 for lighter backgrounds, or 1/200th for darker). if you cant get the background as light as you want, adjust your iso a little higher to 400 or maybe even 800. just be sure to set it back as you dont want to much digital noise in your pics. like i said though, i almost always have my camera on 1/125th and adjust the aperature as i wish. you may want to experiment with this and see if it works for you. once you get the hang of things, you will realize that TTL is a great thing. hope this helps a bit.