When you plan on post processing your photos there is a trick you can use to get more detail in the lights and darks in one exposure. For digital, underexposing a bit [up to -2/3 of a stop] is best for retaining details in the highlights. It’s not difficult to pull detail from dark areas in digital photos with an image editing program, but blown out highlights can’t be recovered. For film, overexposing [+2/3 of a stop or even more] works best for capturing and retaining details.
The reason comes down to the way each format captures images (and how as well, don’t rule out film as irrelevant just yet). If your capturing negatives, then the area that the light hits on the film turns dark. These dark areas on the film are actually the highlights when transfered as a positive print. Exposing it longer captures more detail throughout and there is more to work with than just clear film. The opposite is true of digital because it’s not capturing a negative. The area the light hits is corresponds to the highlights. Overexposing will lead to less detail to work with.
In addition to that, digital sensors don’t have the ability to capture a wide range of values in the highlight end of the spectrum. Negative film is special in that it is able to retain remarkable amounts of detail even in somewhat extreme overexposure. Details can later be recovered when printing or converting to digital. A white digital image is basically the same as a clear negative…if that all makes any sense…
So why should you care about this? No more washed out skies in landscape photos! 🙂