How do you maximize/minimize dynamic range?

For a long time now I have been struggling with this question, so maybe some of you can steer me in the right direction...

There are times when I have trouble getting the desired dynamic range out of my camera. This applies more to topside photography, but does have some applications in the wet. Here are 2 examples...

When there is bright sun in part of the picture and another picture is in the shade I have troube getting both into the useable range.... either the bright areas are blown out and the shaddows are correct, or the shaddows are black and the bright areas are properly exposed. In this situation, what can be done to minimize dynamic range?

When the sky is overcast I often end up with pictures that have a uniform exposure throughought. They appear very flat and almost monochrome (I mean that figuratively). In this situation, is there anything that can be done to maximize dynamic range?

I understand that in some situations, there may be no good solution, but is there anything that can minimize these issues? camera settings? filters? etc.?

Thanks in advance for any help....

Examine your histogram after the shot and make sure it touches both sides if you can. That's how you maximize your dynamic range. Sometimes this means punching some flash in to fill the shadows. You can always add contrast later, but while actually making the photo you want to capture information in all levels. A well exposed photo will almost always look flat right out of the camera...

Cheers

James

If you shoot RAW, you have the option of doing two (or more) separate conversions in Photoshop ACR (or another converter) with different exposure levels - one representing the normal optimum exposure, and another over-exposed by one stop (or even more) to pull more information out of the shadows. If there are areas that are slightly blown out in the optimum version, a final under-exposed (one stop or less) version may help solve that.

After combining the three conversions as layers in a single image, you will still have a lot of work left to do, selectively erasing parts of the three different layers and playing with opacity and fill to end up with a good composite, but for the right image, it's worth it.

This technique is analogous to (but cruder than) the method topside landscape photographers have used for years in order to expand dynamic range, shooting multiple versions of the same scene with different exposure settings with the camera on a tripod, and then sandwiching the negatives together or selectively printing using different parts of the differentl exposed negatives.

Another classic topside trick is to use a graduated neutral density filter to compress the dynamic range. Since you can't control the position of the transition point on a camera and lens in a housing, you would have to preset the position of the filter before the dive. I've never heard of anyone using ND grad filters underwater. but split diopters - half neutral density and half clear (and usually about a +2 diopter strength) are commonly used for over-unders, essentially solving the same problem.

If the sun is in the frame, then you probably will need to stop down and use artificial illumination for the near subject. This can take fairly powerful strobes that can push a lot of light.

As James said, adding contrast to an image that looks a bit flat isn't difficult, and is almost always necessary at least to some degree. Levels is the classic photoshop tool, but Curves provides a lot more control. Even better, convert the image to LAB color space and learn to use Curves there.

Frogfish

Robert's post is pretty comprehensive. I'd just add that if you're shooting JPEG rather than RAW, you can use a custom tone curve loaded in your camera to improve both contrast and rendering of highlights and shadows.