Ok, I give up! Getting good pictures at Monterey...

[Brewski]

I can adjust the strobes manually. Should I go with shutter priority instead of aperture priority? I could go to ISO200 or 400 but was afraid of excessive noise.

Neither, go full manual. the camera can't make decent decisions underwater.
Shoot at ISO 100, for macro I shoot at ISO 64. Like chuck said earlier a faster shutter speed and small aperture will get you better results. the stobes are bright so you can stop down a lot with them.

Wide you may need the faster ISO, but when were in the bay the close up stuff photographs better due to the so so vis we get locally.

 

[mikerault]

Should I use the diffusers or just leave them naked? (The strobes!)

 

[Brewski]

I use the diffusers for both wide and macro. Wide to even out the hot spots. and macro to soften the same.

these shots used the diffusers

This one I didn't

 

[cricfanSD]

Actually due to the high mass and neutral buoyancy, you can hand hold at
fairly long exposures UW. I've done as slow as 1/8 with my 13mm (on a full
frame film camera, that's like a 9mm on your 20D).

Chuck, not to nitpick on you, but 1/8 is not way below the hand holding threshold for a 13mm lens assuming Velvia 100. Well for 20 or 35mm it is definitely very slow speed.

Mainak

 

[mikerault]

Love the Nudi!

 

[Chuck Tribolet]

Chuck, not to nitpick on you, but 1/8 is not way below the hand holding threshold for a 13mm lens assuming Velvia 100. Well for 20 or 35mm it is definitely very slow speed

Film speed affects what shutter speed you need, not how slow you
can hand hold.

The general rule of thumb for surface photography with a full
frame sensor is that you can hand hold down to 1/focal length.
So for a 13mm, that would be 1/13 second. And I have real
problems on the surface at 1/focal length.

 

[cricfanSD]

Film speed affects what shutter speed you need, not how slow you
can hand hold.

The general rule of thumb for surface photography with a full
frame sensor is that you can hand hold down to 1/focal length.
So for a 13mm, that would be 1/13 second. And I have real
problems on the surface at 1/focal length.

Yes that is true. The comment about ISO was to know whether you need that slow speed because you use 50/100 slide films or just because of poor light. Digital guys can still crank up their gain to avoid the 1/focal length requirement. Anyway I do agree with you irrespective of what lens you use 1/8 is difficult to hand hold on surface.