Recently I went with a fellow photographers to photograph rhododendrons which are common on eastern hills of Olympic mountains. We were hoping for fog to have a good separation of rhododendron bushes from trees in background.
There was fog but not where we needed it. The only option left was to use shallow depth of field. My fixed 50mm lens got second life. I had not used it for a while but it was most appropriate in that case since it had the widest aperture of all my lenses.
The other options was to let it blend with with forest, make it part of it.
Did I mention there was fog but not where we needed it? Well, we ended up spending most of the time photographing that fog that was somewhere else:
Fog Over Lowlands
Fog Over Puget Sound