The sky often makes an image, but the only time it will expose the same as the land is when the whole scene is bright and sunny. Now that may be fine for tourist brochures / postcards, but if you want some drama in the landscape it’s not the best conditions to photograph in as bright sunshine tends to give a dull flat image due to the lack of shadows.
If you want interesting light to add depth to your images, then taking them without any thought given to the difference in exposure between the sky and ground will result in either dark ground, or more likely, a white sky with any detail burnt out.
Our eyes balance out this light difference, but the camera needs some help to do this. A polarising filter can be used to darken the sky if the exposure difference is not too great. It has to be used with care to ensure it isn’t darkened too much to make it look unreal, but it can give a real boost to images and bring out the clouds.
When the exposure difference is large, there are two options available:
- use neutral density graduated filters to block out some of the light from the sky and balance the exposure. This gets the exposure correct at the time of taking and so requires no post-processing, but you need to get the filter in the correct position and constantly check the light levels. If you have trees on the horizon on a windy day, or are struggling to keep the tripod firmly anchored, this option may be the only one.
- bracket your exposures and combine the exposure which is correct for the ground with the one which is correct for the sky. This is quicker at the time of taking, but requires post-processing and fills up your computer with multiple images. If you have a sharp V-shaped valley, then this option may be essential to stop the tops of the valley sides being darkened by filters
When I used film, I used option 1 for 90% of the time. Now I use digital, I use both options depending on the situation.
Slide-show illustrating the combining of two exposures: