Le Pradet near Cap Garonne in ProvenceAn other one with the
Hoya ND 400 filter giving a 90 seconds exposure in this early and cloudy morning.
Some days ago i received an email from a reader of my
french website asking how to determine the exposure time in this kind of images.
On most DSLRs the exposure metering stops at 30s. What to do when you need more ?
First, if you're not familiar with long exposures you can try the
scientific method :) Increase the lens aperture (decrease the number) and/or the ISO speed until you reach some values where your camera can meter. Then return to your real settings and try a little extrapolation. If your camera says 25s at f14 and ISO 400 you can try a 100s exposure at f14 and ISO 100, but it's an
approximative value.
With digital and when the light is stable you can first try your scientificaly computed settings, look at the histogram and adjust. But at dusk time for example the light can decrease rapidly. If you try a 90 seconds exposure, look at the histogram and find it too much on the left you will want to try 120 seconds but it will probably be too late and increasing the exposure length will just increase the digital noise in your files ...
So my real advice would be : try, practice, learn to know the light until you become good at guessing the right settings without iterating tries.