How do I......

[Gizmo]

Stop a complete white out whilst using my strobe when shooting wide angle.... haven't even tried macro yet?

[Mark]

When I do WA shots I have to put the strobe on its lowest setting with the most obscure diffuser for shot between 4-5 feet, then gradually less diffuser strength before I go full strength with the strobe. Its always a bit a of a pain as I have to take the same shot so many times to get one lit half as well as I would like.

I am sure there will be someone a lot more experienced than me on here to tell you how to do it properly.

As for macro, I use no diffuser and max power for the best lighting!

[Mike W]

I use the same sort of idea as Mark.

When I get my camera ready I set it to 1/125sec and f8 with both strobes switched to half power. That gives me a decent exposure at about 2 to 3 feet. If the subject is further away I first try to get closer, then increase the strobe power. If it's closer I angle the strobes further out to use the edge of their beams and reduce illumination.

After I've taken a shot at my basic settings I review the pic and the histogram and shoot again, if necessary. The histogram tells me if the overall lighting is OK, the pic tells me if the balance of foreground flashlight and background ambient light looks OK. Foreground lighting is changed by changing the flash power, background lighting by changing the shutter speed. I seldom alter the aperture.

My favourite thing about digital is that I can review and reshoot underwater.

[Ding]

Supose I'm lucky My Oly has TTL so I never have to think about the strobe, as long as the spotting light is on the subject the camera does the rest....

Sounds easy--- but if it was everybody could do it...

[Ding]

Originally Posted by Ding

Supose I'm lucky My Oly has TTL so I never have to think about the strobe, as long as the spotting light is on the subject the camera does the rest....

Had to get a new strobe cable £70. When the guy in cameras underwater said Ikelite were not cheap he was not kidding.

[Mattdiver]

Originally Posted by Gizmo

Stop a complete white out whilst using my strobe when shooting wide angle.... haven't even tried macro yet?

It's actually easy to get it in the right ballpark if you know the guide number of your strobe (check in your manual).

Divide the guide number by the distance between strobe and subject, and set the aperture to that number.

E.g. Assuming the Ike 150 is a GN30 (don't know the actual value) and you're 5ft away from your subject, set your aperture to 30/5 = 6 (or the nearest value, say F5.6).

Then you adjust your shutter speed to balance background light. If that makes shutter speed too slow (say less than 1/15s) because of little available ambient light, then consider reducing strobe power and/or adding a diffuser.

Last note: the GN is based on your camera being set to ISO 100, and goes up proportionately if the ISO is set higher.

[M J Marshall]

Can anyone explain what happens to this equation if the ISO is increased/reduced to 50?

Does the guide number double or is the relationship different. I am yet to get underwater with my new strobe but it would be useful to understand this before I get wet.

Cheers
MJM

[TimIngmire]

Sure, IIRC increasing ISO from 50 to 100, or 100 to 200 increases the light sensitivity by 1 stop. So keeping everything else constant, you should be able to increase your aperture by stop to keep the overall exposure the same but you would also increase your depth of field ie. more of the picture in focus.

You maight want a 2nd opinion on that tho.

Tim

[KenByrne]

Tim you are correct 50 - 100 is 1 stop 100 - 200 is 1 stop and 200-400 is 1 stop.

With flash underwater the shutter speed controls the background exposure so a fast shutter speed will give a dark background and slower shutter speeds a lighter background depending on the aperture and available light.

So if you increase the ISO from say 50 - 100 you can decrease the aperture by 1 stop which confusingly means increasing the F number.

For example if everything else stayed the same if the correct aperture at ISO 50 is F4 then the following would all give the same exposure.

ISO 50 F4
ISO 100 F5.6
ISO 200 F8
ISO 400 F11
ISO 800 F16
ISO 3200 F22

The guide number gives the correct aperture for a given ISO at a given flash to subject distance. Be aware that the guide numbers are often given in air and they will underexpose at the given distance when used underwater. Even if given as underwater distances they will not expose correctly if the water conditions are substantially different from the test conditions.

Ken

[Charlie H]

One simple way to reduce back scatter that I have found works is to introduce ambient light. Try setting the camera just 1 stop below what the light meter indicates but set the strobes on the correct setting for the camera to subject distance. Don't worry if this leads you to use a slow shutter speed as the flash light should freeze the subject.