Wetpixel Live: ISO Guide for Underwater Photographers

Traditionally, photography textbooks concentrated on aperture and shutter speed as being the most important ways to control exposure. Modern digital cameras offer another option, namely ISO. For underwater photographers, often shooting in quite low light levels and trying to balance flash and natural light, ISO offers an excellent tool to help control the way we capture light underwater. @adamhanlon and @Alex_Mustard discuss the newer camera technology that allows this and how they use it when shooting.

ISO is one of the most misunderstood concepts of digital photography and that is because a camera has only one sensor and therefore only one film. You can't go and change the film you can only proxy that with gain which is what ISO maps to

You can't generalise concepts due to the different way sensors are constructed so one camera may be totally fine at 2500 and one be rubbish. Also some cameras are ISO invariant and some are not at all and this influences how you should shoot.

Only one thing is for sure an image with too low ISO that is too dark on broad area is worse than one with a small clipped highlight in my opinion

If you want to maximised performance in your camera I suggest you study not only DR charts but also input referred noise charts

For those who did not understand my previous post what I am saying is that the advice given in the video to shoot wide angle between ISO 100 and 640 will be appropriate for the camera @Alex_Mustard shoots but not on another one that has a different design

Nikon cameras use Sony sensor but are designed in a completely different way from Sony or Panasonic cameras that use the same sensor family not only that some sensors are front illuminated and some are back illuminated and those behave differently

Finally cameras do not meter the same way so if you take brand A and say -1/3 works well as the camera cannot meter perfectly in water you may find another one where it needs +1/3 

Know your camera in detail in essence is the motto