What’s the effect? If there is a slight breeze ruining a reflection when shooting rivers or lakes, there is a solution: use a long exposure to smooth out the water and improve the reflection. If you are shooting at sunrise or sunset, the exposure times may naturally run to several seconds, but if you are shooting during the day, you will need a neutral density filter.
What’s the time? This image of Thurne Mill reflected in the river needed an exposure of five seconds to smooth the surface of the water, as a light breeze detracted from the overall tranquility of the scene. Would it have made the reflection better if I’d used a longer exposure time? Not really, as the water’s as smooth as it can be, and there wasn’t any other benefit of using a longer exposure, because there weren’t any substantial clouds.
When there is the possibility of getting some interesting movement in clouds, I use my Lee Little or Big Stopper with a landscape polariser to obtain a longer exposure (see page 35). My Lee landscape polariser is ultra-thin, so is great for using with wide-angle lenses without running the risk of vignetting.