There are essentially two situations when you may want to use a long exposure. The most obvious is in low light or at night when exposure times may need to be as long as several seconds, minutes or even hours to capture enough light to produce a well-exposed image.
But you may also want to use long exposure photography techniques when the light is much brighter – to blur moving water or blur cloud movement, for example.
In this case you can use dark filters to extend exposure times considerably, as we’ll reveal in this tutorial on how to perfect your long-exposure photography techniques.
How to set up your camera for long exposure photography: steps 1-2
Shooting long exposures introduces a greater likelihood of camera shake, so it’s a good idea to get into good habits when it comes to preparing to take your shot.
It goes without saying that a tripod is essential, but it’s equally important to set your tripod up properly so that it won’t move during the exposure.
If working on soft terrain or wet sand, push part of the lower legs into the ground until the tripod is rock steady.
In windy conditions keep the tripod low to the ground and spread the legs wider to increase stability.
Having the camera securely mounted on a steady tripod is the first step to preventing camera shake, but you also need to prevent any vibrations when you actually take the shot.
Using a remote release is good practice, or you can use the two-second self-timer so you don’t have to touch the camera.
To stop internal vibrations caused by the mirror slapping up when the shutter is released, either use your camera’s mirror lock-up function (if it has one) or take the shot in Live View mode, which also locks up the mirror.
How to set up your camera for long exposure photography: steps 3-5
Exposures of up to 30 seconds are possible in modes such as Aperture Priority, but for longer exposures you’ll need to use the Bulb setting.
This allows the shutter to be held open manually for as long as required. This is best done using a lockable remote release.
Press the button on the release to open the shutter and then lock it open for the required time.
Some remote releases have a built-in timer for a precise exposure, but you can just use a watch with a second hand.
For exposures of longer than 30 seconds you can’t take a meter reading in the usual way. Instead, you need a reference exposure to work from.
One way to do this is to drastically increase the ISO setting to enable you to take a meter reading.
Then use this value to calculate what the exposure time needs to be at a lower ISO.
So, if the exposure is 4 secs at ISO1600, it needs to be 60 secs at ISO100 to give the same exposure (4 secs at ISO1600 = 8 secs at ISO800 = 15 secs at ISO400 = 30 secs at ISO200 = 60 secs at ISO100).
In bright lighting situations where you want to produce a creative effect such as blurry water, it’s possible to increase the exposure time by using filters.
A polarising filter, for example, will increase the exposure time required for a correct exposure by around two stops – for example from ¼ sec to 1 sec.
Neutral density (ND) filters enable you to lengthen the exposure further. ND filters come in different strengths and can extend the exposure from between one and ten stops.
A ten-stop filter would lengthen an exposure of 1/30 sec to 30 seconds.
source: http://www.digitalcameraworld.com/2014/10/24/long-exposure-photography-how-to-set-up-your-camera/
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