長時間曝光技巧及心得(Long exposure technique and how-to)
In between the seasons of Spring and Summer, there is a landscape of the moss growing in the NE Taiwan coast, especially in a grooved rocks shore called “Lau Mei”, in between groove the milky water formed by the waves turn out to be a strong contrast with the moss on the rocks during the Low/ high tides, it needs to know the timing of the tides every day before the tour to get a good shoot.
You need to use tripod for a slow shutter speed to get the long exposure effects, such as the flowing of the waves, for getting a deep depth of field (DoF), you should set a f/stop of 16 or higher, so the image will be sharp from in front of the lens to the infinity, I would like to set f/18, the reason is too small exposure like f/22 or smaller might cause vignettes and chromatic aberrations depends on the lens.
The key point of the long exposure technique is the shutter speed, with tripod we can set as long as we want the shutter speed, normally it should be more than a second as the starting point to get the effect, the longer the shutter speed the result of the image can be more soft and calm, such as the motion of the cloud moving、sea wave slapping etc.. I set normally 4 seconds or more, under the bright ambient I should use the neutral density filter normally over 5 stops to reduce the light.
As to the ISO setting, normally should be the lowest of the camera ISO value for a clean image , it might be different from camera to camera, for example ISO100 is for Canon.
至於要獲得大景深及銳利的效果，拍攝時須關閉相機自動對焦(AF)功能，做法為先以自動對焦在鏡頭前找一對焦點，至於要在多遠處須依不同相機的CoC(Circles of confusion)值、鏡頭焦段及光圈大小等3個數據來計算，網路上有一手機App “DOF Master”可使用，用時輸入相機種類、鏡頭焦距和光圈值即可獲得對焦點的距離。
For deeper DoF and sharper image, first step you should close the auto focusing function of the camera and use manual, the way to do is to find a focus distance first by AF (auto focusing) of the camera, regarding to how far this focus distance should be depending on camera format (CoC,Circles of confusion)、lens focal length and f/stops, there is an app on the web called “DOF Master” can be used to quickly calculate the focusing distance after importing the camera format、lens focal length and f/stop.
I like to use the light meter (Seknoic L-758DR) for a better operation, the softer-ware of the meter can find the middle point of your individual camera’s exposure, in practical you don’t need to do many test shots to get the appropriate one.