Mongolia, 4 minutes exposure.
Mongolia, 4 minutes exposure.

By long exposures I mean longer than, say, the 30secs that most cameras offer as the longest built in exposure time. The Leica M goes up to 60 secs, the Leica S, to 120 secs but for other cameras you may need to buy an external camera release that will work with the camera in B (Bulb) mode.

The idea of a very long exposure is to let moving objects blur to add drama, but at the same time  keeping the rest of the image sharp. Seascapes are a good example of this where the sea goes all misty and smooth, but clouds also add a lot of drama when they are hugely blurred like in the shot above.

If the light levels are really low, like pre-dawn or under moonlight, it’s easy to get long exposures but during the day you won’t be able to get a long enough exposure without using a Neutral Density filter which reduces the amount of light entering the lens. You’ll need a very strong one too – at least 7 stops, preferably 10 or more. Such a filter (10 stops) will change a sunny daylight exposure of, say, 1/60 sec @ f16 to 16.0 sec @f16. That is going to give you good blurry water effects but for clouds you need far longer. Add a second filter, like 3 stop ND, and you can now get 2 mins – barely enough, depending on now quickly the clouds are moving. Add a 5 stop filter and you end up at 8 mins which should be ample for clouds.

Buy good filters, cheap one can have a colour cast although this is not too hard to correct in Lightroom. You’ll also want optically high quality ones too – no point in putting cheap glass in front of you expensive lenses!

I always take a 10-stop ND with me, you never know when a good opportunity might crop up.