The two problems I speak of are lack of depth of field and high contrast, particularly in landscape photography.
Combining multiple exposures in Photoshop is a technique often applied to the problem of dealing with high contrast, for example to darken bright skies and bring a more even exposure range across a landscape.
Some photographers even claim that you don’t need ND filters anymore, just take two exposures and combine them using layers in Photoshop. Job done.
However the technique of combining exposures can also be used to solve other photographic problems. A less known strategy is to use two exposures to increase depth of field. Here’s how:
Focus your lens so that the area of sharp focus stretches from the middle distance to the horizon. Then refocus so that the entire foreground is sharp.
Now combine the two exposure using layers in Photoshop. Remove the unsharp areas using a layer mask. You can find out more about layer masks here in a handy little tutorial here and a more advanced article here.
The result is final image which is pin sharp from foreground to horizon.
You can of course apply both the adjustment to the focus and the exposure at the same time. The only thing to watch out for is to not change the aperture when you’re compensating for exposure, only the shutterspeed. If you change the aperture your images will not line up properly.
I hope you’ve found these techniques useful.